FIGURE 1: NEWS MEDIA FEAR OF A COMING ICE AGE

FIGURE 2: NORTHERNHEMISPHERE LAND

FIGURE 3: SOUTHERNHEMISPHERE LAND

FIGURE 4: NORTHERNHEMISPHERE OCEAN

FIGURE 5:  SOUTHERNHEMISPHERE OCEAN

[LIST OF POSTS ON THIS SITE]

1. The warming trend that began since the Industrial Revolution (coincidental with the end of the Little Ice Age or LIA) after the year 1850 has been attributed to rising atmospheric carbon dioxide concentration in terms of its theoretical heat trapping effect. In turn, rising atmospheric CO2 is attributed to emissions from fossil fuel combustion in the industrial economy. The carbon from fossil fuels is thought of as a perturbation of the carbon cycle and climate system with external carbon dug up from deep under the ground where it had been sequestered for millions of years. The warming trend is thus attributed to the industrial economy and described as artificial (Callendar 1938), human caused(Hansen 1981), anthropogenic (IPCC 2007).
2. Yet, it is generally recognized that CO2 driven Anthropogenic Global Warming (AGW) was interrupted with significant cooling for a period of 30 years or more even as carbon dioxide from the industrial economy was being released into the atmosphere at record rates. The cooling occurred at some time after the 1930s and before the 1980s with the cooling anomaly generally described as 1940s to 1970s. The cooling trend in this period is recorded in the instrumental temperature record and in global and regional temperature reconstructions. News media archives from that period show a global fear of a return to the Little Ice Age (Figure 1) even though the recovery from the LIA is also feared as catastrophic human caused global warming.
3. This cooling period is considered to be anomalous and contentious because it appears to be incompatible with the theory of AGW. Skeptics often use this cooling period to argue against AGW theory. Proponents of AGW have either minimized its importance in terms of climate change theory and consensus among climate scientists (Peterson 2008) or have offered explanations for the cooling within the context of global warming. It is argued that the cooling may be explained in terms that are not inconsistent with AGW. For example, it is possible that climate instability is an effect of AGW and the brief period of cooling is an outcome of such instability (Asakura 1981) (Allen 1982) (Suckling 1984).
4. It is also proposed that an artificial effect of the industrial economy,in addition to the generation of artificial carbon dioxide, is an increase in atmospheric aerosols. It is known that aerosols can cause cooling. Here we examine the aerosol argument in some detail as it is the generally accepted theory of the anomalous 1940s-1970s cooling period in the era of AGW. References to the literature are listed in the AEROSOL BIBLIOGRAPHY below.
5. Empirical evidence of cooling in a period of approximately 30 to 40 years at some time between 1940 and 1980 is presented in Figure 2 to Figure 5 using regional temperature reconstructions provided by the Hadley Centre Climate Research Unit of the Met Office of the Government of the UK. Four distinct regions, that together encompass the globe, are studied separately. These are LAND areas of the Northern (Figure 2) and Southern (Figure 3) hemispheres and OCEAN areas of the Northern (Figure 4) and Southern (Figure 5) hemispheres. Each figure is a GIF animation that shows a trend profile for each of the twelve calendar months, one month at a time and cycles through all twelve calendar months. Each graphic is a display of the temperature trend in a moving 15-year window. A horizontal line is drawn at the zero trend position. Warming trends (above the zero line) are colored Red and Cooling trends (below the zero line) are colored Blue. Although the data are provided from 1850, only the portion after 1918 is shown for greater clarity of the study period of 1940 to 1980.
6. We find in these charts that all four regions and all twelve calendar months show 15yr cooling periods of various degrees of persistence and intensity at somewhat different locations within the study period of 1940-1980 within a global warming context. The period 1918-2017 is dominated by more intense and more persistent episodes of warming. Some cooling periods are found outside the study period particularly so in the 1920s when cooling was more intense and after the year 2000 when cooling is less intense but consistent with the so called “warming hiatus” hypothesis that has been explained in terms of changes in ocean heat content (Related post [Ocean Heat Content] ). The ocean heat content argument is not used for the 1940s-1970s cooling because the cooling is also found in ocean heat content.
7. The location, duration, and intensity of the 1940s-1970s cooling period vary among calendar months, between land and ocean in each hemisphere, and between the two hemispheres for each surface type. However, some kind of a cooling trend is found somewhere within this period. In some cases both short term cooling and warming periods are found. Although cooling dominates, the cooling is not found to be sustained in all cases. It should be noted that a significant and deep blue patch of cooling is seen in the Northern Hemisphere Oceans. This observations is consistent with the cooling in the North Atlantic and Arctic in the 1960s and 1970s described in (Read 1992) & (Hodson 2014).
8. A great deal of aerosols are created in the industrial economy as can be seen in the current problem with haze in rapidly industrializing countries such as China and India. Aerosol was also created in testing of atomic bombs. One way that aerosols can affect surface temperature is their backscatter property in which they reflect solar radiation back into space high up in the stratosphere thus shielding to some extent the lower atmosphere from solar radiation. In 1971, Stephen Schneider (with co-author Rasool) published the defining paper for the explanation of the 1940s-1970s cooling in the context of a longer period of global warming driven by rising atmospheric CO2. He argued that the warming effect of carbon dioxide is logarithmic so that the greater the CO2 concentration the less the effect on the rate of warming of increasing CO2 concentration. However, that relationship is exactly in reverse for aerosol backscatter cooling – the greater the aerosol concentration, the greater is the effect of additional aerosol. Based on these rate considerations, he concluded that in the long term, CO2 warming will be saturated and more easily overcome by aerosol backscatter cooling so that in the limit, at high atmospheric CO2 levels, the principal determinant of surface temperature will be aerosols. The aerosol backscatter cooling hypothesis was widely held and a number of papers were published in support of this explanation of the 1940s-1970s cooling. Notable are the McCormick 1967 paper postulating a relationship between atmospheric turbidity and cooling (turbidity to the non-transparency or haziness of the atmosphere usually caused by aerosols).
9. However, the impact of aerosols on surface temperature is more complex than simple backscatter and its other effects are addressed in many of the papers listed below. Aerosols can warm the atmosphere by absorbing solar radiation and retaining that heat. They can also seed high altitude cloud formation thereby increasing cloud albedo and cause cooling. The general case for cloud albedo as an explanation for the anomalous cooling period is presented by Schneider in his 1972 paper which says in effect that since warming increases cloud formation and therefore cloud albedo, warming can lead to periods of cooling.
10. A specific instance of the warming effect of aerosols relevant to the period under study is found in the so called “Gottschalk curve” attributed to Bernard Gottschalk, Professor of Physics at Harvard University. He found a brief period of warming in global temperature reconstructions towards the end of World War II. A study of the Gottschalk curve is presented in (Herndon 2018). It is argued (by both Gottschalk and Herndon) that the Gottschalk curve is result of aerosol warming by the large amount of aerosols generated by war activities including for example the carpet bombing of Dresden and the nuclear bombs in Hiroshima. The Gottschalk curve appears in many of the frames of the HadCRU temperature data displayed in Figure 2 to Figure 5 as a brief triangular warming period just prior to 1959 (the war ended in 1945). The brief red warming peak is seen in some but not all months for land surfaces. (Herndon 218) uses the Gottschalk curve to highlight the warming effect of aerosols and to propose an alternate theory of AGW in terms of aerosol warming.
11. A special consideration is that of sulfate aerosols as their ultrafine aerosol cooling effect is well known and well documented as seen in (Junge 1961, Wiedensohler 1996) below. In terms of sulfate aerosols, the 1940s-1970s cooling effect can be explained by a rapid increase in hydrogen sulfide (H2S) emissions from the combustion of hydrocarbon fuels before H2S emissions were regulated and eventually almost eliminated. The rapid increase in sulfate aerosol emissions is recorded in environmental history as the age of acid rain. By the end of the 1970s, tight regulation of sulfate emissions by acid rain programs worldwide, had significantly reduced sulfate aerosol emissions . The 1940s-1970s cooling can be understood in that context as well as the resurgent global warming since the 1980s. Yet another causal connection between the acid rain program and global warming is proposed by NASA-GISS. This bizarre theory holds that acid rain kills bacteria in wetlands and reduces the biological production of methane which in turn causes global warming  [LINK]
12. IN SUMMARY: The data provided above show conclusive evidence of an anomalous period of cooling in an overall era of global warming within the context of an industrial economy generating fossil fuel emissions. The cooling anomaly is seen in all four regions of the world defined according to hemisphere and surface (land vs ocean). Significant research references exist that have described the cooling and explained it in terms of aerosol backscatter. The attempt by some climate scientists to minimize the importance of the 1940s-1970s cooling to climate science seems incongruous in the context of the data and research papers presented. The end of the cooling period and the return to warming may be explained by a global response to the acid rain creation of sulfate aerosols that ended sulfate emissions.  

STEPHEN SCHNEIDER

AEROSOLS AND CLIMATE: BIBLIOGRAPHY

1. 1961: Junge, Christian E., and James E. Manson. “Stratospheric aerosol studies.” Journal of Geophysical Research 66.7 (1961): 2163-2182. The stratospheric aerosol layer previously identified by balloon measurements has been studied extensively by means of recovered rod impactor samples obtained during aircraft flights at the 20‐km level from 63°S to 72°N during March–November 1960. From a variety of physical and chemical measurements, which are presented in detail, the conclusion is drawn that this layer is stable, constant in time and space, and composed mainly of sulfate particles. The various questions raised by this result, particularly with respect to collection of micrometeorites, are presented and discussed.</p>
2. 1967: McCormick, Robert A., and John H. Ludwig. “Climate modification by atmospheric aerosols.” Science 156.3780 (1967): 1358-1359. Theoretical considerations and empirical evidence indicate that atmospheric turbidity, a function of aerosol loading, is an important factor in the heat balance of the earth-atmosphere system. Turbidity increase over the past few decades may be primarily responsible for the decrease in worldwide air temperatures since the 1940’s.
3. 1971: Rasool, S. Ichtiaque, and Stephen H. Schneider. “Atmospheric carbon dioxide and aerosols: Effects of large increases on global climate.” Science 173.3992 (1971): 138-141. Effects on the global temperature of large increases in carbon dioxide and aerosol densities in the atmosphere of Earth have been computed. It is found that, although the addition of carbon dioxide in the atmosphere does increase the surface temperature, the rate of temperature increase diminishes with increasing carbon dioxide in the atmosphere. For aerosols, however, the net effect of increase in density is to reduce the surface temperature of Earth. Because of the exponential dependence of the backscattering, the rate of temperature decrease is augmented with increasing aerosol content. An increase by only a factor of 4 in global aerosol background concentration may be sufficient to reduce the surface temperature by as much as 3.5 ° K. If sustained over a period of several years, such a temperature decrease over the whole globe is believed to be sufficient to trigger an ice age.
4. 1971: Mitchell Jr, J. Murray. “The effect of atmospheric aerosols on climate with special reference to temperature near the earth’s surface.” Journal of Applied Meteorology 10.4 (1971): 703-714. A generalized model of the effect of an optically thin atmospheric aerosol on the terrestrial heat budget is proposed, and applied to the problem of estimating the impact of the aerosol on temperatures near the earth’s surface. The distinction between warming and cooling near the surface attributable to the aerosol is found on the basis of this model to depend on whether the ratio of absorption a to backscatter b of incoming solar radiation by the aerosol is greater or less than the critical ratio            (a/b)_O = C(1−A)(1−Ak)/[D(1+A)−C(1−A)], where A is the surface albedo, C the fraction of sensible to total (sensible plus latent) solar heating of the surface, D the fraction of aerosol that is in convective contact with the surface, and k a multiple of b that measures the relative aerosol backscattering efficiency with respect to solar radiation reflected upward from the surface.A distinction is drawn between a stratospheric aerosol (D=0) which generally cools the atmosphere near the surface, and a tropospheric aerosol (D→1) which may either cool or warm the atmosphere near the surface depending on various properties of the aerosol and of the surface itself. Over moist surfaces, such as vegetated areas and oceans, the critical ratio (a/b)_o is of order 0.1. Over drier surfaces, such as deserts and urban areas, (a/b)_o is of order unity. If the actual ratio a/b of most tropospheric aerosols is of order unity, as inferred by previous authors, then the dominant effect of such aerosols is warming except over deserts and urban arms where the effect is somewhat marginal between warming and cooling.Further aerosol climatic effects are found likely to include a slight decrease of cloudiness and precipitation, and an increase of “planetary” albedo above the oceans, although not necessarily above the continents. Suggestions by several previous authors to the effect that the apparent worldwide cooling of climate in recent decades is attributable to large-scale increases of particulate pollution of the atmosphere by human activities are not supported by this analysis.
5. 1972: Schneider, Stephen H. “Cloudiness as a global climatic feedback mechanism: The effects on the radiation balance and surface temperature of variations in cloudiness.” Journal of the Atmospheric Sciences 29.8 (1972): 1413-1422. The effect of variation in cloudiness on the climate is considered in terms of 1) a relation between the radiation balance of the earth-atmosphere system and variations in the amount of cloud cover or effective cloud top height, 2) the effect on the surface temperature of variations in cloudiness, and 3) the dynamic coupling or “feedback” effects relating changes in surface temperature to the formation of clouds. The first two points are studied by numerical integration of a simple radiation flux model, and the third point is discussed qualitatively. Global-average radiation balance calculations show that an increase in the amount of low and middle level cloud cover (with cloud top height and cloud albedo fixed) decreases the surface temperature. But, this result for the global-average case does not hold near polar regions, where the albedo of the cloudy areas can he comparable to (or even smaller than) the albedo of the snow-covered cloudless areas, and where, especially in the winter season, the amount of incoming solar radiation at high latitudes is much less than the global-average value of insolation. The exact latitude at which surface cooling changes to surface warming from a given increase in cloud cover amount depends critically upon the local values of the cloud albedo and the albedo of the cloudless areas that are used in the calculation. However, an increase in effective cloud top height (with cloud cover and cloud albedo fixed) increases the surface temperature at all latitudes.
6. 1974: Chýlek, Petr, and James A. Coakley. “Aerosols and climate.” Science 183.4120 (1974): 75-77. To determine the effects of atmospheric aerosols on the radiative heating of the earth-atmosphere system, the radiative transfer equation is solved analytically in the two-stream approximation. It is found that the sign of the heating is independent of optical thickness of an aerosol layer and the amount of heating approaches a finite limit with increasing thickness of a layer. Limitations of the two-stream approximation are discussed.
7. 1976: Cess, Robert D. “Climate change: An appraisal of atmospheric feedback mechanisms employing zonal climatology.” Journal of the Atmospheric Sciences 33.10 (1976): 1831-1843. The sensitivity of the earth’s surface temperature to factors which can induce long-term climate change, such as a variation in solar constant, is estimated by employing two readily observable climate changes. One is the latitudinal change in annual mean climate, for which an interpretation of climatological data suggests that cloud amount is not a significant climate feedback mechanism, irrespective of how cloud amount might depend upon surface temperature, since there are compensating changes in both the solar and infrared optical properties of the atmosphere. It is further indicated that all other atmospheric feedback mechanisms, resulting, for example, from temperature-induced changes in water vapor amount, cloud altitude and lapse rate, collectively double the sensitivity of global surface temperature to a change in solar constant. The same conclusion is reached by considering a second type of climate change, that associated with seasonal variations for a given latitude zone. The seasonal interpretation further suggests that cloud amount feedback is unimportant zonally as well as globally. Application of the seasonal data required a correction for what appears to be an important seasonal feedback mechanism. This is attributed to a variability in cloud albedo due to seasonal changes in solar zenith angle. No attempt was made to individually interpret the collective feedback mechanisms which contribute to the doubling in surface temperature sensitivity. It is suggested, however, that the conventional assumption of fixed relative humidity for describing feedback due to water vapor amount might not be as applicable as is generally believed. Climate models which additionally include ice-albedo feedback are discussed within the framework of the present results.
8. 1983: Coakley Jr, James A., Robert D. Cess, and Franz B. Yurevich. “The effect of tropospheric aerosols on the Earth’s radiation budget: A parameterization for climate models.” Journal of the Atmospheric Sciences 40.1 (1983): 116-138. Guided by the results of doubling-adding solutions to the equation of radiative transfer, we develop a simple technique for incorporating in climate models the effect of the background tropospheric aerosol on solar radiation. Because the atmosphere is practically nonabsorbing for much of the solar spectrum the effects of the tropospheric aerosol on the reflectivity, transmissivity and absorptivity of the atmosphere are adequately accounted for by the properties of a two-layered system with the atmosphere placed above the aerosol layer. The two-stream and delta-Eddington approximations to the radiative transfer equation then provide reasonably accurate estimates of the changes brought about by the aerosol. Furthermore, results of the doubling-adding calculations lead to a simple parameterization for the distribution of absorption by the aerosol within the atmosphere. Using these simple techniques, we calculate the changes caused by models for the naturally occurring tropospheric aerosol in a zonal mean energy balance climate model. The 2–30°C surface cooling caused by the background aerosol is comparable in magnitude but opposite in sign to the temperature changes brought about by the current atmospheric concentrations of N₂0 and CH₄ and by a doubling of CO₂. The model results also indicate that even though the background aerosol may decrease the planetary albedo at high latitudes, it causes cooling at all latitudes. We also use the simple techniques to calculate the influence of dust on the planetary albedo of a desert. Here we demonstrate that the interaction of the aerosol scattering with the angular dependence of the surface reflectivity strongly influences the planetary albedo.
9. 1987: Charlson, Robert J., et al. “Oceanic phytoplankton, atmospheric sulphur, cloud albedo and climate.” Nature326.6114 (1987): 655. The major source of cloud-condensation nuclei (CCN) over the oceans appears to be dimethylsulphide, which is produced by planktonic algae in sea water and oxidizes in the atmosphere to form a sulphate aerosol Because the reflectance (albedo) of clouds (and thus the Earth’s radiation budget) is sensitive to CCN density, biological regulation of the climate is possible through the effects of temperature and sunlight on phytoplankton population and dimethylsulphide production. To counteract the warming due to doubling of atmospheric CO₂, an approximate doubling of CCN would be needed.
10. 1989: Blanchet, Jean-Pierre. “Toward estimation of climatic effects due to Arctic aerosols.” Atmospheric Environment (1967)23.11 (1989): 2609-2625. During the last decade, the estimation of the climatic implications of principal anthropogenic aerosols (soot and sulphates) has been investigated by observation and modeling efforts at three scales of dimension:(1) the aerosol scale where the optical properties are determined; (2) the kilometer scale where the radiative fluxes and diabatic heating are felt, and finally, (3) the regional and hemispheric scales where the climate questions pertain. This paper reviews the current results on these three scales, with an emphasis on the comparisons between observations and model results.
11. 1990: Hansen, James E., and Andrew A. Lacis. “Sun and dust versus greenhouse gases: An assessment of their relative roles in global climate change.” Nature 346.6286 (1990): 713. Many mechanisms, including variations in solar radiation and atmospheric aerosol concentrations, compete with anthropogenic greenhouse gases as causes of global climate change. Comparisons of available data show that solar variability will not counteract greenhouse warming and that future observations will need to be made to quantify the role of tropospheric aerosols, for example.
12. 1992: Clarke, Antomy D. “Atmospheric nuclei in the remote free-troposphere.” Journal of atmospheric chemistry 14.1-4 (1992): 479-488. During May-June of 1990 an extensive flight series to survey aerosol present in the upper-troposphere was undertaken aboard the NASA DC-8 as part of the CLObal Backscatter Experiment (GLOBE). About 50,000 km were characterized between 8–12 km altitude and between 70°N and 58°S. Aerosol with diameters greater than 3nm were counted and sized with a combination of condensation nuclei counters and optical particle counters. Aerosol number and mass concentrations were separately identified with regard to both refractory and volatile components. Regions of the free-troposphere with the lowest mass concentrations were generally found to have the highest number concentrations and appeared to be effective regions for new particle production. These new particle concentrations appear inversely related to available aerosol surface area and their volatility suggests a sulfuric acid composition. The long lifetime of these new particles aloft can result in their growth to sizes effective as CN and CCN that can be mixed throughout the troposphere.
13. 1992: Charlson, Robert J., et al. “Climate forcing by anthropogenic aerosols.” Science 255.5043 (1992): 423-430. Although long considered to be of marginal importance to global climate change, tropospheric aerosol contributes substantially to radiative forcing, and anthropogenic sulfate aerosol in particular has imposed a major perturbation to this forcing. Both the direct scattering of shortwave solar radiation and the modification of the shortwave reflective properties of clouds by sulfate aerosol particles increase planetary albedo, thereby exerting a cooling influence on the planet. Current climate forcing due to anthropogenic sulfate is estimated to be –1 to –2 watts per square meter, globally averaged. This perturbation is comparable in magnitude to current anthropogenic greenhouse gas forcing but opposite in sign. Thus, the aerosol forcing has likely offset global greenhouse warming to a substantial degree. However, differences in geographical and seasonal distributions of these forcings preclude any simple compensation. Aerosol effects must be taken into account in evaluating anthropogenic influences on past, current, and projected future climate and in formulating policy regarding controls on emission of greenhouse gases and sulfur dioxide. Resolution of such policy issues requires integrated research on the magnitude and geographical distribution of aerosol climate forcing and on the controlling chemical and physical processes.
14. 1993: Kiehl, J. T., and B. P. Briegleb. “The relative roles of sulfate aerosols and greenhouse gases in climate forcing.” Science260.5106 (1993): 311-314. Calculations of the effects of both natural and anthropogenic tropospheric sulfate aerosols indicate that the aerosol climate forcing is sufficiently large in a number of regions of the Northern Hemisphere to reduce significantly the positive forcing from increased greenhouse gases. Summer sulfate aerosol forcing in the Northern Hemisphere completely offsets the greenhouse forcing over the eastern United States and central Europe. Anthropogenic sulfate aerosols contribute a globally averaged annual forcing of –0.3 watt per square meter as compared with +2.1 watts per square meter for greenhouse gases. Sources of the difference in magnitude with the previous estimate of Charlson et al. are discussed.
15. 1994: Schneider, Stephen H. “Detecting climatic change signals: are there any” fingerprints“?.” Science 263.5145 (1994): 341-347. Projected changes in the Earth’s climate can be driven from a combined set of forcing factors consisting of regionally heterogeneous anthropogenic and natural aerosols and land use changes, as well as global-scale influences from solar variability and transient increases in human-produced greenhouse gases. Thus, validation of climate model projections that are driven only by increases in greenhouse gases can be inconsistent when one attempts the validation by looking for a regional or time-evolving “fingerprint” of such projected changes in real climatic data. Until climate models are driven by time-evolving, combined, multiple, and heterogeneous forcing factors, the best global climatic change “fingerprint” will probably remain a many-decades average of hemispheric-scale to global-scale trends in surface air temperatures. Century-long global warming (or cooling) trends of 0.5°C appear to have occurred infrequently over the past several thousand years—perhaps only once or twice a millennium, as proxy records suggest. This implies an 80 to 90 percent heuristic likelihood that the 20th-century 0.5 ± 0.2°C warming trend is not a wholly natural climatic fluctuation.
16. 1995: Pilinis, Christodoulos, Spyros N. Pandis, and John H. Seinfeld. “Sensitivity of direct climate forcing by atmospheric aerosols to aerosol size and composition.” Journal of Geophysical Research: Atmospheres 100.D9 (1995): 18739-18754. We evaluate, using a box model, the sensitivity of direct climate forcing by atmospheric aerosols for a “global mean” aerosol that consists of fine and coarse modes to aerosol composition, aerosol size distribution, relative humidity (RH), aerosol mixing state (internal versus external mixture), deliquescence/crystallization hysteresis, and solar zenith angle. We also examine the dependence of aerosol upscatter fraction on aerosol size, solar zenith angle, and wavelength and the dependence of single scatter albedo on wavelength and aerosol composition. The single most important parameter in determining direct aerosol forcing is relative humidity, and the most important process is the increase of the aerosol mass as a result of water uptake. An increase of the relative humidity from 40 to 80% is estimated for the global mean aerosol considered to result in an increase of the radiative forcing by a factor of 2.1. Forcing is relatively insensitive to the fine mode diameter increase due to hygroscopic growth, as long as this mode remains inside the efficient scattering size region. The hysteresis/deliquescence region introduces additional uncertainty but, in general, errors less than 20% result by the use of the average of the two curves to predict forcing. For fine aerosol mode mean diameters in the 0.2–0.5 μm range direct aerosol forcing is relatively insensitive (errors less than 20%) to variations of the mean diameter. Estimation of the coarse mode diameter within a factor of 2 is generally sufficient for the estimation of the total aerosol radiative forcing within 20%. Moreover, the coarse mode, which represents the nonanthropogenic fraction of the aerosol, is estimated to contribute less than 10% of the total radiative forcing for all RHs of interest. Aerosol chemical composition is important to direct radiative forcing as it determines (1) water uptake with RH, and (2) optical properties. The effect of absorption by aerosol components on forcing is found to be significant even for single scatter albedo values of ω=0.93–0.97. The absorbing aerosol component reduces the aerosol forcing from that in its absence by roughly 30% at 60% RH and 20% at 90% RH. The mixing state of the aerosol (internal versus external) for the particular aerosol considered here is found to be of secondary importance. While sulfate mass scattering efficiency (m² (g SO₄²⁻)⁻¹) and the normalized sulfate forcing (W (g SO₄²⁻)⁻¹) increase strongly with RH, total mass scattering efficiency (m² g⁻¹) and normalized forcing (W g⁻¹) are relatively insensitive to RH, wherein the mass of all species, including water, are accounted for. Following S. Nemesure et al. (Direct shortwave forcing of climate by anthropogenic sulfate aerosol: sensitivity to particle size, composition, and relative humidity, submitted to Journal of Geophysical Research, 1995), we find that aerosol feeing achieves a maximum at a particular solar zenith angle, reflecting a balance between increasing upscatter fraction with increasing solar zenith angle and decreasing solar flux (from Rayleigh scattering) with increasing solar zenith angle.
17. 1996: Wiedensohler, Alfred, et al. “Occurrence of an ultrafine particle mode less than 20 nm in diameter in the marine boundary layer during Arctic summer and autumn.” Tellus B 48.2 (1996): 213-222. The International Arctic Ocean Expedition 1991 (IAOE‐91) provided a platform to study the occurrence and size distributions of ultrafine particles in the marine boundary layer (MBL) during Arctic summer and autumn. Measurements of both aerosol physics, and gas/particulate chemistry were taken aboard the Swedish icebreaker Oden. Three separate submicron aerosol modes were found: an ultrafine mode (D_p < 20 nm), the Aitken mode (20 < D_p < 100 nm), and the accumulation mode (D_p > 100 nm). We evaluated correlations between ultrafine particle number concentrations and mean diameter with the entire measured physical, chemical, and meteorological data set. Multivariate statistical methods were then used to make these comparisons. A principal component (PC) analysis indicated that the observed variation in the data could be explained by the influence from several types of air masses. These were characterised by contributions from the open sea or sources from the surrounding continents and islands. A partial least square (PLS) regression of the ultrafine particle concentration was also used. These results implied that the ultrafine particles were produced above or in upper layers of the MBL and mixed downwards. There were also indications that the open sea acted as a source of the precursors for ultrafine particle production. No anti‐correlation was found between the ultrafine and accumulation particle number concentrations, thus indicating that the sources were in separate air masses.
18. 1995: Andreae, Meinrat O. “Climatic effects of changing atmospheric aerosol levels.” World survey of climatology 16 (1995): 347-398. 
19. 1997: Raes, Frank, et al. “Observations of aerosols in the free troposphere and marine boundary layer of the subtropical Northeast Atlantic: Discussion of processes determining their size distribution.” Journal of Geophysical Research: Atmospheres 102.D17 (1997): 21315-21328. During July 1994, submicron aerosol size distributions were measured at two sites on Tenerife, Canary Islands. One station was located in the free troposphere (FT), the other in the marine boundary layer (MBL). Transport toward these two sites was strongly decoupled: the FT was first affected by dust and sulfate‐laden air masses advecting from North Africa and later by clean air masses originating over the North Atlantic, whereas the MBL was always subject to the northeasterly trade wind circulation. In the FT the submicron aerosol distribution was predominantly monomodal with a geometric mean diameter of 120 nm and 55 nm during dusty and clean conditions, respectively. The relatively small diameter during the clean conditions indicates that the aerosol originated in the upper troposphere rather than over continental areas or in the lower stratosphere. During dusty conditions the physical and chemical properties of the submicron aerosol suggest that it has an anthropogenic origin over southern Europe and that it remains largely externally mixed with the supermicron mineral dust particles during its transport over North Africa to Tenerife. Apart from synoptic variations, a strong diurnal variation in the aerosol size distribution is observed at the FT site, characterized by a strong daytime mode of ultrafine particles. This is interpreted as being the result of photoinduced nucleation in the upslope winds, which are perturbed by anthropogenic and biogenic emissions on the island. No evidence was found for nucleation occurring in the undisturbed FT. The MBL site was not strongly affected by European pollution during the period of the measurements. The MBL aerosol size distribution was bimodal, but the relative concentration of Aitken and accumulation mode varied strongly. The accumulation mode can be related to cloud processing of the Aitken mode but also to pollution aerosol which was advected within the MBL or entrained from the FT. No bursts of nucleation were observed within the MBL.
20. 1997: Andreae, Meinrat O., and Paul J. Crutzen. “Atmospheric aerosols: Biogeochemical sources and role in atmospheric chemistry.” Science 276.5315 (1997): 1052-1058. Atmospheric aerosols play important roles in climate and atmospheric chemistry: They scatter sunlight, provide condensation nuclei for cloud droplets, and participate in heterogeneous chemical reactions. Two important aerosol species, sulfate and organic particles, have large natural biogenic sources that depend in a highly complex fashion on environmental and ecological parameters and therefore are prone to influence by global change. Reactions in and on sea-salt aerosol particles may have a strong influence on oxidation processes in the marine boundary layer through the production of halogen radicals, and reactions on mineral aerosols may significantly affect the cycles of nitrogen, sulfur, and atmospheric oxidants.
21. 1997: Hansen, J., Mki Sato, and R. Ruedy. “Radiative forcing and climate response.” Journal of Geophysical Research: Atmospheres 102.D6 (1997): 6831-6864. We examine the sensitivity of a climate model to a wide range of radiative forcings, including changes of solar irradiance, atmospheric CO₂, O₃, CFCs, clouds, aerosols, surface albedo, and a “ghost” forcing introduced at arbitrary heights, latitudes, longitudes, seasons, and times of day. We show that, in general, the climate response, specifically the global mean temperature change, is sensitive to the altitude, latitude, and nature of the forcing; that is, the response to a given forcing can vary by 50% or more depending upon characteristics of the forcing other than its magnitude measured in watts per square meter. The consistency of the response among different forcings is higher, within 20% or better, for most of the globally distributed forcings suspected of influencing global mean temperature in the past century, but exceptions occur for certain changes of ozone or absorbing aerosols, for which the climate response is less well behaved. In all cases the physical basis for the variations of the response can be understood. The principal mechanisms involve alterations of lapse rate and decrease (increase) of large‐scale cloud cover in layers that are preferentially heated (cooled). Although the magnitude of these effects must be model‐dependent, the existence and sense of the mechanisms appear to be reasonable. Overall, we reaffirm the value of the radiative forcing concept for predicting climate response and for comparative studies of different forcings; indeed, the present results can help improve the accuracy of such analyses and define error estimates. Our results also emphasize the need for measurements having the specificity and precision needed to define poorly known forcings such as absorbing aerosols and ozone change. Available data on aerosol single scatter albedo imply that anthropogenic aerosols cause less cooling than has commonly been assumed. However, negative forcing due to the net ozone change since 1979 appears to have counterbalanced 30–50% of the positive forcing due to the increase of well‐mixed greenhouse gases in the same period. As the net ozone change includes halogen‐driven ozone depletion with negative radiative forcing and a tropospheric ozone increase with positive radiative forcing, it is possible that the halogen‐driven ozone depletion has counterbalanced more than half of the radiative forcing due to well‐mixed greenhouse gases since 1979.
22. 2000: Robock, Alan. “Volcanic eruptions and climate.” Reviews of Geophysics 38.2 (2000): 191-219. Volcanic eruptions are an important natural cause of climate change on many timescales. A new capability to predict the climatic response to a large tropical eruption for the succeeding 2 years will prove valuable to society. In addition, to detect and attribute anthropogenic influences on climate, including effects of greenhouse gases, aerosols, and ozone‐depleting chemicals, it is crucial to quantify the natural fluctuations so as to separate them from anthropogenic fluctuations in the climate record. Studying the responses of climate to volcanic eruptions also helps us to better understand important radiative and dynamical processes that respond in the climate system to both natural and anthropogenic forcings. Furthermore, modeling the effects of volcanic eruptions helps us to improve climate models that are needed to study anthropogenic effects. Large volcanic eruptions inject sulfur gases into the stratosphere, which convert to sulfate aerosols with an e‐folding residence time of about 1 year. Large ash particles fall out much quicker. The radiative and chemical effects of this aerosol cloud produce responses in the climate system. By scattering some solar radiation back to space, the aerosols cool the surface, but by absorbing both solar and terrestrial radiation, the aerosol layer heats the stratosphere. For a tropical eruption this heating is larger in the tropics than in the high latitudes, producing an enhanced pole‐to‐equator temperature gradient, especially in winter. In the Northern Hemisphere winter this enhanced gradient produces a stronger polar vortex, and this stronger jet stream produces a characteristic stationary wave pattern of tropospheric circulation, resulting in winter warming of Northern Hemisphere continents. This indirect advective effect on temperature is stronger than the radiative cooling effect that dominates at lower latitudes and in the summer. The volcanic aerosols also serve as surfaces for heterogeneous chemical reactions that destroy stratospheric ozone, which lowers ultraviolet absorption and reduces the radiative heating in the lower stratosphere, but the net effect is still heating. Because this chemical effect depends on the presence of anthropogenic chlorine, it has only become important in recent decades. For a few days after an eruption the amplitude of the diurnal cycle of surface air temperature is reduced under the cloud. On a much longer timescale, volcanic effects played a large role in interdecadal climate change of the Little Ice Age. There is no perfect index of past volcanism, but more ice cores from Greenland and Antarctica will improve the record. There is no evidence that volcanic eruptions produce El Niño events, but the climatic effects of El Niño and volcanic eruptions must be separated to understand the climatic response to each.
23. 2001: Jacobson, Mark Z. “Strong radiative heating due to the mixing state of black carbon in atmospheric aerosols.” Nature409.6821 (2001): 695. Aerosols affect the Earth’s temperature and climate by altering the radiative properties of the atmosphere. A large positive component of this radiative forcing from aerosols is due to black carbon—soot—that is released from the burning of fossil fuel and biomass, and, to a lesser extent, natural fires, but the exact forcing is affected by how black carbon is mixed with other aerosol constituents. From studies of aerosol radiative forcing, it is known that black carbon can exist in one of several possible mixing states; distinct from other aerosol particles (externally mixed^{1,2,3,4,5,6,7}) or incorporated within them (internally mixed^1,3,7), or a black-carbon core could be surrounded by a well mixed shell⁷. But so far it has been assumed that aerosols exist predominantly as an external mixture. Here I simulate the evolution of the chemical composition of aerosols, finding that the mixing state and direct forcing of the black-carbon component approach those of an internal mixture, largely due to coagulation and growth of aerosol particles. This finding implies a higher positive forcing from black carbon than previously thought, suggesting that the warming effect from black carbon may nearly balance the net cooling effect of other anthropogenic aerosol constituents. The magnitude of the direct radiative forcing from black carbon itself exceeds that due to CH₄, suggesting that black carbon may be the second most important component of global warming after CO₂in terms of direct forcing.
24. 2002: Kaufman, Yoram J., Didier Tanré, and Olivier Boucher. “A satellite view of aerosols in the climate system.” Nature419.6903 (2002): 215. Anthropogenic aerosols are intricately linked to the climate system and to the hydrologic cycle. The net effect of aerosols is to cool the climate system by reflecting sunlight. Depending on their composition, aerosols can also absorb sunlight in the atmosphere, further cooling the surface but warming the atmosphere in the process. These effects of aerosols on the temperature profile, along with the role of aerosols as cloud condensation nuclei, impact the hydrologic cycle, through changes in cloud cover, cloud properties and precipitation. Unravelling these feedbacks is particularly difficult because aerosols take a multitude of shapes and forms, ranging from desert dust to urban pollution, and because aerosol concentrations vary strongly over time and space. To accurately study aerosol distribution and composition therefore requires continuous observations from satellites, networks of ground-based instruments and dedicated field experiments. Increases in aerosol concentration and changes in their composition, driven by industrializationand an expanding population, may adversely affect the Earth’s climate and water supply.
25. 2002: Menon, Surabi, et al. “Climate effects of black carbon aerosols in China and India.” Science 297.5590 (2002): 2250-2253. In recent decades, there has been a tendency toward increased summer floods in south China, increased drought in north China, and moderate cooling in China and India while most of the world has been warming. We used a global climate model to investigate possible aerosol contributions to these trends. We found precipitation and temperature changes in the model that were comparable to those observed if the aerosols included a large proportion of absorbing black carbon (“soot”), similar to observed amounts. Absorbing aerosols heat the air, alter regional atmospheric stability and vertical motions, and affect the large-scale circulation and hydrologic cycle with significant regional climate effects.
26. 2005: Andreae, Meinrat O., Chris D. Jones, and Peter M. Cox. “Strong present-day aerosol cooling implies a hot future.” Nature 435.7046 (2005): 1187. Atmospheric aerosols counteract the warming effects of anthropogenic greenhouse gases by an uncertain, but potentially large, amount. This in turn leads to large uncertainties in the sensitivity of climate to human perturbations, and therefore also in carbon cycle feedbacks and projections of climate change. In the future, aerosol cooling is expected to decline relative to greenhouse gas forcing, because of the aerosols’ much shorter lifetime and the pursuit of a cleaner atmosphere. Strong aerosol cooling in the past and present would then imply that future global warming may proceed at or even above the upper extreme of the range projected by the Intergovernmental Panel on Climate Change.
27. 2005: Pöschl, Ulrich. “Atmospheric aerosols: composition, transformation, climate and health effects.” Angewandte Chemie International Edition 44.46 (2005): 7520-7540. Aerosols are of central importance for atmospheric chemistry and physics, the biosphere, climate, and public health. The airborne solid and liquid particles in the nanometer to micrometer size range influence the energy balance of the Earth, the hydrological cycle, atmospheric circulation, and the abundance of greenhouse and reactive trace gases. Moreover, they play important roles in the reproduction of biological organisms and can cause or enhance diseases. The primary parameters that determine the environmental and health effects of aerosol particles are their concentration, size, structure, and chemical composition. These parameters, however, are spatially and temporally highly variable. The quantification and identification of biological particles and carbonaceous components of fine particulate matter in the air (organic compounds and black or elemental carbon, respectively) represent demanding analytical challenges. This Review outlines the current state of knowledge, major open questions, and research perspectives on the properties and interactions of atmospheric aerosols and their effects on climate and human health.
28. 2005: Jickells, T. D., et al. “Global iron connections between desert dust, ocean biogeochemistry, and climate.” science 308.5718 (2005): 67-71. The environmental conditions of Earth, including the climate, are determined by physical, chemical, biological, and human interactions that transform and transport materials and energy. This is the “Earth system”: a highly complex entity characterized by multiple nonlinear responses and thresholds, with linkages between disparate components. One important part of this system is the iron cycle, in which iron-containing soil dust is transported from land through the atmosphere to the oceans, affecting ocean biogeochemistry and hence having feedback effects on climate and dust production. Here we review the key components of this cycle, identifying critical uncertainties and priorities for future research.
29. 2005: Lohmann, Ulrike, and Johann Feichter. “Global indirect aerosol effects: a review.” Atmospheric Chemistry and Physics5.3 (2005): 715-737.  Aerosols affect the climate system by changing cloud characteristics in many ways. They act as cloud condensation and ice nuclei, they may inhibit freezing and they could have an influence on the hydrological cycle. While the cloud albedo enhancement (Twomey effect) of warm clouds received most attention so far and traditionally is the only indirect aerosol forcing considered in transient climate simulations, here we discuss the multitude of effects. Different approaches how the climatic implications of these aerosol effects can be estimated globally as well as improvements that are needed in global climate models in order to better represent indirect aerosol effects are discussed in this paper.
30. 2009: Ramanathan, Veerabhadran, and Yan Feng. “Air pollution, greenhouse gases and climate change: Global and regional perspectives.” Atmospheric environment 43.1 (2009): 37-50. Greenhouse gases (GHGs) warm the surface and the atmosphere with significant implications for rainfall, retreat of glaciers and sea ice, sea level, among other factors. About 30 years ago, it was recognized that the increase in tropospheric ozone from air pollution (NO_x, CO and others) is an important greenhouse forcing term. In addition, the recognition of chlorofluorocarbons (CFCs) on stratospheric ozone and its climate effects linked chemistry and climate strongly. What is less recognized, however, is a comparably major global problem dealing with air pollution. Until about ten years ago, air pollution was thought to be just an urban or a local problem. But new data have revealed that air pollution is transported across continents and ocean basins due to fast long-range transport, resulting in trans-oceanic and trans-continental plumes of atmospheric brown clouds (ABCs) containing sub micron size particles, i.e., aerosols. ABCs intercept sunlight by absorbing as well as reflecting it, both of which lead to a large surface dimming. The dimming effect is enhanced further because aerosols may nucleate more cloud droplets, which makes the clouds reflect more solar radiation. The dimming has a surface cooling effect and decreases evaporation of moisture from the surface, thus slows down the hydrological cycle. On the other hand, absorption of solar radiation by black carbon and some organics increase atmospheric heating and tend to amplify greenhouse warming of the atmosphere. ABCs are concentrated in regional and mega-city hot spots. Long-range transport from these hot spots causes widespread plumes over the adjacent oceans. Such a pattern of regionally concentrated surface dimming and atmospheric solar heating, accompanied by widespread dimming over the oceans, gives rise to large regional effects. Only during the last decade, we have begun to comprehend the surprisingly large regional impacts. In S. Asia and N. Africa, the large north-south gradient in the ABC dimming has altered both the north-south gradients in sea surface temperatures and land–ocean contrast in surface temperatures, which in turn slow down the monsoon circulation and decrease rainfall over the continents. On the other hand, heating by black carbon warms the atmosphere at elevated levels from 2 to 6 km, where most tropical glaciers are located, thus strengthening the effect of GHGs on retreat of snow packs and glaciers in the Hindu Kush-Himalaya-Tibetan glaciers. Globally, the surface cooling effect of ABCs may have masked as much 47% of the global warming by greenhouse gases, with an uncertainty range of 20–80%. This presents a dilemma since efforts to curb air pollution may unmask the ABC cooling effect and enhance the surface warming. Thus efforts to reduce GHGs and air pollution should be done under one common framework. The uncertainties in our understanding of the ABC effects are large, but we are discovering new ways in which human activities are changing the climate and the environment.
31. 2009: Jimenez, Jose L., et al. “Evolution of organic aerosols in the atmosphere.” science 326.5959 (2009): 1525-1529. Organic aerosol (OA) particles affect climate forcing and human health, but their sources and evolution remain poorly characterized. We present a unifying model framework describing the atmospheric evolution of OA that is constrained by high–time-resolution measurements of its composition, volatility, and oxidation state. OA and OA precursor gases evolve by becoming increasingly oxidized, less volatile, and more hygroscopic, leading to the formation of oxygenated organic aerosol (OOA), with concentrations comparable to those of sulfate aerosol throughout the Northern Hemisphere. Our model framework captures the dynamic aging behavior observed in both the atmosphere and laboratory: It can serve as a basis for improving parameterizations in regional and global models.
32. 2017: Stanley, S. (2017), Satellite data reveal effects of aerosols in Earth’s atmosphere, Eos, 98,https://doi.org/10.1029/2017EO069945. Published on 24 March 2017.  Earth’s atmosphere is dusted with tiny particles known as aerosols, which include windblown ash, sea salt, pollution, and other natural and human-produced materials. Aerosols can absorb or scatter sunlight, affecting how much light reflects back into space or stays trapped in the atmosphere. Despite aerosols’ known impact on Earth’s temperature, major uncertainties plague current estimates of their overall effects, which in turn limit the certainty of climate change models. In an effort to reduce this uncertainty, Lacagnina et al. have combined new satellite data, providing, for the first time, data on aerosols’ ability to absorb or reflect light globally, through model simulations In this new study, the team focused on the direct effects of aerosols on shortwave radiation in 2006. These effects depended on the particles’ vertical location with respect to clouds, the reflective properties of the underlying land or water, and the optical properties of the aerosol particles themselves, including how much light they are prone to scatter or absorb.The researchers used instruments aboard the French Polarization and Anisotropy of Reflectances for Atmospheric Science coupled with Observations from a Lidar (PARASOL) satellite and NASA’s Aura spacecraft to measure aerosol optical properties around the world. Data from NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS) satellite instrument provided measurements of cloud characteristics and land reflectance, and an aerosol climate model known as ECHAM5-HAM2 helped fill in any gaps in the observations. Using these data, calculations of the global average radiative effect for 2006 revealed an overall cooling effect due to aerosols. At regional scales, however, different mixtures of aerosols led to widely varying effects. For example, the cooling effects of aerosols were larger in the Northern Hemisphere because of higher pollution emissions and infiltration by desert dust. Overall, the heat transfer measurements in this study were consistent with past measurements using other methods. The authors call for additional studies that also integrate data from multiple sources and for improved global measurements of aerosol absorption to better understand and predict the future effects of aerosols on climate change.
33. 2017: Lacagnina, Carlo, Otto P. Hasekamp, and Omar Torres. “Direct radiative effect of aerosols based on PARASOL and OMI satellite observations.” Journal of Geophysical Research: Atmospheres 122.4 (2017): 2366-2388. Accurate portrayal of the aerosol characteristics is crucial to determine aerosol contribution to the Earth’s radiation budget. We employ novel satellite retrievals to make a new measurement‐based estimate of the shortwave direct radiative effect of aerosols (DREA), both over land and ocean. Global satellite measurements of aerosol optical depth, single‐scattering albedo (SSA), and phase function from PARASOL (Polarization and Anisotropy of Reflectances for Atmospheric Sciences coupled with Observations from a Lidar) are used in synergy with OMI (Ozone Monitoring Instrument) SSA. Aerosol information is combined with land‐surface bidirectional reflectance distribution function and cloud characteristics from MODIS (Moderate Resolution Imaging Spectroradiometer) satellite products. Eventual gaps in observations are filled with the state‐of‐the‐art global aerosol model ECHAM5‐HAM2. It is found that our estimate of DREA is largely insensitive to model choice. Radiative transfer calculations show that DREA at top‐of‐atmosphere is −4.6 ± 1.5 W/m² for cloud‐free and −2.1 ± 0.7 W/m² for all‐sky conditions, during year 2006. These fluxes are consistent with, albeit generally less negative over ocean than, former assessments. Unlike previous studies, our estimate is constrained by retrievals of global coverage SSA, which may justify different DREA values. Remarkable consistency is found in comparison with DREA based on CERES (Clouds and the Earth’s Radiant Energy System) and MODIS observations.
34. 2018: Ralph Kahn, NASA, Aerosol Remote Sensing and Modeling, 2018. [FULL TEXT] The global scope of aerosol environmental influences makes satellite remote sensing a key tool for the study of these particles. Desert dust storms, wildfire smoke and volcanic ash plumes, and urban pollution palls on hot, cloud-free summer days are among the most dramatic manifestations of aerosol particles visible in satellite imagery [LINK] .  Our group includes the core aerosol science team for the NASA Earth Observing System’s MODerate resolution Imaging Spectroradiometer (MODIS)instruments, and the aerosol scientist for the Multi-angle Imaging SpectroRadiometer (MISR).The MODIS Dark Target, Deep Blue, and MAIAC aerosol algorithms are developed and maintained here, along with the MISR Research Aerosol Retrieval algorithm. We also contribute to the Total Ozone Mapping Spectrometer (TOMS) the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) and the Suomi National Polar-orbiting Partnership’s Visible Infrared Imaging Radiometer Suite (SNPP-VIIRS) aerosol retrieval algorithms. We perform validation studies on all these satellite aerosol products using ground-based remote-sensing aerosol measurements, such as those provided by the global Aerosol Robotic Network (AERONET) of Sun- and sky-scanning photometers and the Micro-Pulse Lidar Network (MPLNet). And through the Goddard Interactive Online Visualization ANd aNalysis Infrastructure (GIOVANNI), we have participated in the development of web-based tools to collocate multiple satellite and AERONET products and to analyze them statistically. In addition, we have developed and maintain a state-of-the-art, ground-based mobile facility for measuring the physical and chemical properties of aerosol and clouds, along with the ambient radiation fields (SMART-COMMIT-ACHIEVE), and the Cloud Absorption Radiometer (CAR) deployed in an aircraft nosecone, that can obtain radiance measurements over the entire sphere in 14 spectral bands. The aerosol applications which we lead, and to which we contribute, range from the fundamental radiative transfer used in satellite aerosol retrieval algorithms, to detailed studies of wildfire smoke and volcanic ash plumes, aerosol pollution events and long-term exposure, as well as large-scale aerosol transports, global energy balance assessments, and climate change studies.
35. 2018: Herndon, J. Marvin. “Air Pollution, Not Greenhouse Gases: The Principal Cause of Global Warming.” 2018: Time series of global surface temperature presentations often exhibit a bump coincident with World War II (WW2) as did one such image on the front page of the January 19, 2017 New York Times. Intrigued by the front-page New York Times graph, Bernie Gottschalk of Harvard University applied sophisticated curve-fitting techniques and demonstrated that the bump, which shows a global burst in Earth temperature during WW2, is a robust feature showing up in eight independent NOAA databases, four land and four oceans. The broader activities of WW2, especially those capable of altering Earth’s delicate energy balance by particulate aerosols can be generalized to post-WW2 global warming. Increases in aerosolized particulates over time is principally responsible for the concomitant global warming increases. Proxies for global particulate pollution – increasing global coal and crude oil production, as well as aviation fuel consumption – rise in strikingly parallel fashion to the rise in global temperature as shown in the accompanying figure. The World War II wartime particulate-pollution had the same global-warming consequence as the subsequent ever-increasing global aerosol particulate-pollution from (1) increases in aircraft and vehicular traffic, and the industrialization of China and India with their smoke stacks spewing out smoke and coal fly ash, as well as from recently documented studies that show (2) coal fly ash [is being] covertly jet-sprayed into the region where clouds form on a near-daily, near-global basis. It is further noted that the integrity of [IPCC] models and assessments is compromised, because of their failure to take into account the aerosolized pollution particulates that have been intentionally and covertly sprayed into the atmosphere for decades in the region where clouds form. Instead of cooling Earth, as many scientists still believed it would, covert military geoengineering activity increases global warming.
    [FULL TEXT]

ATMOSPHERIC TURBIDITY BIBLIOGRAPHY

1. 1964: Ångström, Anders. “The parameters of atmospheric turbidity.” Tellus 16.1 (1964): 64-75. The methods for evaluating the atmospheric turbidity parameters, introduced by the present author in 1929–30, are subjected to a critical examination. A method first suggested by M. Herovanu (1959) is here simplified and expanded, and used for deriving the named parameters in adherence to a procedure described by the present author in a previous paper in this journal (1961). The procedure is applied to the pyrheliometric observations at Potsdam in 1932–36, published by Hoelper (1939) A comparison between the frequency distribution of the coefficient of wave‐length dependence α at the high level station Davos and the low level station Potsdam gives results which are discussed in detail. In all the figures of the present paper, where the turbidity coefficients occur, they are multiplied by 10³.
2. 1967: McCormick, Robert A., and John H. Ludwig. “Climate modification by atmospheric aerosols.” Science 156.3780 (1967): 1358-1359. Theoretical considerations and empirical evidence indicate that atmospheric turbidity, a function of aerosol loading, is an important factor in the heat balance of the earth-atmosphere system. Turbidity increase over the past few decades may be primarily responsible for the decrease in worldwide air temperatures since the 1940′s.
3. 1969: Flowers, E. C., R. A. McCormick, and K. R. Kurfis. “Atmospheric turbidity over the United States, 1961–1966.” Journal of Applied Meteorology 8.6 (1969): 955-962. Five years of turbidity measurements from a network of stations in the United States are analyzed. Measurements are made with the Volz sunphotometer; the instrument, its calibration, and its use are described. The relationship of these measurements to those of Linke and Ångström is briefly discussed. Analysis of the data indicates the following: 1) an annual mean pattern of low turbidity (near 0.05) over the western plains and Rocky Mountains and high turbidity (near 0.14) in the east; 2) observed minimum turbidity near 0.02; 3) an annual cycle of low turbidity in winter and high in summer; 4) lowest turbidity in continental polar air masses and highest in maritime tropical; and 5) no noticeable lowering of turbidity following precipitation.
4. 1972: Lovelock, James E. “Atmospheric turbidity and CCl3F concentrations in rural southern England and southern Ireland.” Atmospheric Environment (1967) 6.12 (1972): 917-925. The seasonal changes in atmospheric turbidity in rural Southern England and Southern Ireland have been observed and are compared with wind direction and with the concentration of CCl₃F a material whose origins are unequivocally anthropogenic. The observations suggest that the dense summertime aerosol is probably an end product of the atmospheric photochemistry of air pollutants and that Continental Europe is the principal source.
5. 1979: Carlson, Toby N. “Atmospheric turbidity in Saharan dust outbreaks as determined by analyses of satellite brightness data.” Monthly Weather Review 107.3 (1979): 322-335. Using VHRR brightness data obtained from the NOAA 3 satellite, isopleths of aerosol Optical depth for Saharan dust have been drawn for seven days during summer 1974 over a portion of the eastern equatorial North Atlantic. The large-scale patterns reveal an elongated dust plume which emerges from a narrow region along the African coast. Thereafter, the plume moves westward and spreads laterally though maintaining rather discrete boundaries associated with sharp gradients of turbidity, especially along the southern border. Exceptionally large values of optical depth (>2.0) are found near the centers of some dust outbreaks but these high values contribute Little to the total dust loading, which, in typical episodes, are estimated to represent a loss of topsoil from Africa of ∼8 million metric tons of material in a period of 4–5 days. There appeared to be no direct intrusion of the dust plume into the ITCZ or north of 25°N in that region. Outbreaks of dust appear often to be in the rear of a well-developed easterly wave disturbance and inverted V-shaped cloud pattern. This paper demonstrates the feasibility of using satellite brightness data to quantitatively map dust outbreaks.
6. 1981: Peterson, James T., et al. “Atmospheric turbidity over central North Carolina.” Journal of Applied Meteorology 20.3 (1981): 229-241. Some 8500 observations of atmospheric turbidity, taken at Raleigh, North Carolina from July 1969 to July 1975 are analyzed for within-day and day-to-day variations and their dependence on meteorological parameters. The annual average turbidity of 0.147 (0.336 aerosol optical thickness) is near the highest non-urban turbidity in the United States. A distinct diurnal turbidity cycle was evident with a maximum in early afternoon. Annually, highest turbidity and day-to-day variation occurred during summer with lowest values and variation during winter. Daily averages revealed an asymmetric annual cycle, with a minimum on 1 January and a maximum on 1 August. Turbidity showed a slight inverse dependence on surface wind speed. Aside from winter, highest turbidities occurred with southeast surface winds. Turbidity was directly proportional to both humidity and dew point. Correlations between turbidity and local visibility were best for visibilities <7 mi. Air mass trajectories arriving at Raleigh were used to study the dependence of turbidity on synoptic air mass. Air masses with a southern origin had greatest turbidities. Turbidity of an air mass significantly increased as the residence time of that air mass over the continental United States increased, with the most rapid changes during summer. A combination of Raleigh (1969–present) and Greensboro, North Carolina (1965–76) records showed a distinct summer increase through 1976, but no change during winter. A linear regression of annual averages for the complete record gave an 18% per decade turbidity increase.
7. 1982: Shaw, Glenn E. “Atmospheric turbidity in the polar regions.” Journal of Applied meteorology 21.8 (1982): 1080-1088. Analysis is presented of 800 measurements of atmospheric monochromatic aerosol optical depth made poleward of ∼65° latitude. The atmosphere of the southern polar region appears to be uncontaminated but is charged with a background aerosol having a mean size of 0.1 μm radius, an almost constant mixing ratio throughout the troposphere, a sea level optical depth (λ = 500 nm) of ∼0.025 and an inferred columnar mass loading of 4-15 × 10⁻⁷ g cm⁻².At around the time of spring equinox the northern polar region (all longitudes) is invaded with Arctic Haze, an aerosol showing a strong anthropogenic chemical fingerprint. The optical depth anomaly introduced by this man-caused haze is τ₀ ≈ 0.110 and the associated columnar mass loading is ∼1.5 × 10⁻⁶ g cm⁻². Turbidity measured seven decades ago at the solar observatory at Uppsala (60°N), suggests that Arctic optical depth has been rising at a rate of dτ/dt ≈ 0.01 ± 0.005 per decade.
8. 1994: Jacovides, C. P., et al. “Atmospheric turbidity parameters in the highly polluted site of Athens basin.” Renewable Energy4.5 (1994): 465-470. Data on atmospheric turbidity coefficients, i.e. Linke factor T_L and Angstrom coefficient β, calculated from measurements of broad-band filter at Athens Observatory (NOA), are reported. A linear model fitted to β vs T_L for Athens is similar to the models reported for Avignon (France) and Dhahran (Saudi Arabia). The variation in the monthly average values of β and T_L is of similar trend to that of Avignon and Dhahran. However, Athens has shown higher values of atmospheric turbidity coefficients than Avignon and similar turbidity levels to Dhahran. Finally, the long-term variation of the monthly mean values of the mid-day turbidity parameters and the broad-band direct and diffuse irradiances under cloudless skies are evaluated for the same period. The turbidity trends in conjunction with the trends of solar radiation components reflect the rapid urbanization and industrialization of the Athens basin.
9. 1994: Gueymard, Christian. “Analysis of monthly average atmospheric precipitable water and turbidity in Canada and northern United States.” Solar Energy 53.1 (1994): 57-71. Atmospheric turbidity and precipitable water data are necessary as inputs to solar radiation or daylight availability models, and to daylighting simulation programs. A new model is presented to obtain precipitable water from long-term averages of temperature and humidity. Precipitable water data derived from this model are tabulated for some Canadian and northern U.S. sites. A discussion on the available turbidity data is presented. An analysis of the datasets from the WMO turbidity network is detailed. The effect of volcanic eruptions is discussed, as well as the possible comparisons with indirect determinations of turbidity from radiation data. A tabulation of the monthly average turbidity coefficients for ten Canadian stations and seven northern U.S. stations of the WMO network is presented.

OTHER THEORIES OF COOLING DURING AGW: BIBLIOGRAPHY

1. 1961: Budyko, Mikhail Ivanovich. “The heat balance of the earth’s surface.” Soviet Geography 2.4 (1961): 3-13. The article discusses the present state of knowledge of the basic components of the heat balance of the earth’s surface (radiation balance, loss of heat to evaporation, turbulent heat exchange) and the distribution of these components in time and space. Soviet research is concerned with applying heat-balance data to the study of physical-geographical processes (hydrologic regime, plant and soil cover), to the study of integrated geographic problems (geographic zonality) and practical problems (weather and hydrologic forecasting, the use of solar energy for productive purposes, and the use of heat-balance data for planning reclamation projects and other nature-transforming measures
2. 1969: Budyko, Mikhail I. “The effect of solar radiation variations on the climate of the earth.” tellus 21.5 (1969): 611-619. It follows from the analysis of observation data that the secular variation of the mean temperature of the Earth can be explained by the variation of short-wave radiation, arriving at the surface of the Earth. In connection with this, the influence of long-term changes of radiation, caused by variations of atmospheric transparency on the thermal regime is being studied. Taking into account the influence of changes of planetary albedo of the Earth under the development of glaciations on the thermal regime, it is found that comparatively small variations of atmospheric transparency could be sufficient for the development of quaternary glaciations.  [FULL TEXT]
3. 1978: Angell, J. K., and J. Korshover. “Global temperature variation, surface-100 mb: An update into 1977.” Monthly Weather Review 106.6 (1978): 755-770. Based on a network of 63 well-spaced radiosonde stations around the world, the global temperature within the surface to 100 mb layer was lower in 1976 than in any year since commencement of the record in 1958, and the 1976 surface temperature equated the global record for the lowest temperature set in 1964; but even so the trend in global temperature since 1965 has been small compared to the 0.5°C decrease during 1960–65. Between 1958 and 1976 the surface to 100 mb temperature in north extratropics decreased by about 1°C, with the decrease twice as great in winter as in summer, and in 1976 this region was 0.2°C lower than in any previous year of record. During the northern winter of 1976–77, both temperate zones were very cold but the polar and tropical zones were quite warm, so that in the hemispheric or global average the season was not anomalous. In the Eastern Hemisphere of the northern extratropics there has been considerable surface warming during the past decade (although a cooling aloft), and this may explain the Soviet concern with warming related to carbon dioxide emissions. There has been a slight overall increase in temperature in the tropics since 1965, mostly in the Western Hemisphere, on which have been superimposed large and significant temperature variations of about a three-year period. These variations, probably related to the Southern Oscillation (and recently not so pronounced), extend in obvious fashion also into north extratropics, and should be taken into account for diagnoses and prognoses in northern latitudes. The rate of increase of carbon dioxide at Mauna Loa and the South Pole is augmented in the warm phase of the tropical oscillation, presumably because of a relation between atmospheric and oceanic temperature. There is evidence for a consistent quasi-biennial variation in temperature at all latitudes, with the temperature approximately 0.1°C higher than average about six months prior to the quasi-biennial west wind maximum at 50 mb in the tropics. The spatial and temporal variability in temperature have tended to increase over the period of record, in accord with the increase in meridional temperature gradient in both hemispheres and the indicated increase in lapse rate in the Northern Hemisphere.  [FULL TEXT]
4. 1981: Asakura, T., and S. Ikeda. “Recent climatic change and unusual weather in the northern hemisphere.” GeoJournal 5.2 (1981): 113-116. Occurrence frequency of unusual weather caused by anomalous synoptic patterns has its peaks in the middle latitude regions and the subtropical regions. Height anomaly patterns at the 500 mb level for the last three decades show the expansion of negative area in the northern hemisphere, resulting in increase of variability in space and time.
5. 1982: Perry, Allen. “Is the climate becoming more variable?.” Progress in Physical Geography 6.1 (1982): 108-114. 
6. 1984: Suckling, Philip W. “TRENDS IN MONTHLY TEMPERATURE DEPARTURES FOR THE CONTINGUOUS UNITED STATES, 1940-1983.” Physical Geography 5.2 (1984): 150-163. A temperature departure index is calculated for each month of the year for 10 regions within the contiguous United States utilizing a total of 193 sites for the 44-year period 1940 to 1983. Five-year moving averages of the index values are plotted on graphs for each region by month in an attempt to detect trends toward an increase or decrease in the occurrence of well above or well below normal monthly temperatures in recent years. Considerable regional differences are found with respect to the size and temporal trend of monthly temperature departures. For example, the Northwest and Southwest regions are often exceptions to the average national trend supporting the concept of considerable east-west differences in temperature variation patterns. Only April, June and December show increases in temperature departure index values in the most recent years for a majority of regions while the summer months of July and August do not exhibit a clear national trend. For a majority of months (January, February, March, May, September, October, November), there has been a decrease in the occurrence of unusually above or below normal monthly temperatures for most regions during the late 1970s/early 1980s.
7. 1984: Suckling, Philip W. “Temperature variability in Georgia in recent years.” Southeastern Geographer 24.1 (1984): 30-41. Southeastern Geographer Vol. 24, No. 1, May 1984,  In recent years several examples of temperature extremes have occurred in Georgia and across the southeast. These include extreme cold in the winter of 1976—77, above normal summer temperatures in 1980 and 1981, and the exceptionally warm Christmas season of 1982. Do these occurrences indicate that temperature variability has increased? Some writers have suggested that there has been an increase in climatic variability in recent years. The following are some relevant quotes: “droughts, floods, heat waves and cold spells unprecedented in living memory “; “record low temperatures reported with increasing frequency in many parts of the United States”; and “the range of short-term variations has widened since the middle of the century.” (J) Studies have addressed the issue of whether the climatic trend is towards cooling or warming. (2) Although the issue of climatic trends of cooling versus warming is important, it is the frequency of extremes (i.e., climatic variability) that may be of more significance to man and his activities, especially in agriculture. (3) In the past, it has been suggested that overall climatic cooling should cause increased temperature variability. However, a study by Van Loon and Williams indicated this concept to be wrong. (4) Previous studies on temperature variability have supported the contention that in recent years an increase in the frequency of extremes has occurred. Asakura and Ikeda concluded that an increase in temperature extremes for the northern hemisphere has occurred in the last two decades compared to the mid-twentieth century . (5) Similarly, Jones, Wigley and Kelly found increased year-toyear variability during the 1970s in a study of northern hemisphere temperature variations over the last century. (6) By contrast, Ratcliffe, Weiler and Collison in a study covering parts of Britain found no trend toward increased climatic variability in the last century. (7) In an assessment of interannual temperature variability for the United States * The technical assistance of Jeon Lee is gratefully acknowledged. Dr. Suckling is Associate Professor of Geography at the University of Georgia in Athens, GA 30602. Vol. XXIV, No. 1 31 since 1896, Chico and Sellers found a decrease in variability for the 1930s to the 1970s. (S) Boer and Higuchi found no evidence to support the contention that the climate has generally become more variable in the northern hemisphere for the last 25 years although, in a later article, they did find evidence suggesting increased summertime temperature variability. (9) Hoyt has shown that the popular opinion that more weather “records” have been set in recent years in the United States is mistaken. If anything, less “records” are being established than statistically expected. (JO) Regional differences in climatic change and variability are to be expected. (JJ) Using a limited number of sites, the study by Van Loon and Williams found decreasing temperature variability for U.S. locations in the midwest and northeast but increasing variability in the south and west. (J2) It is the purpose of the present study to assess temperature variability for the southern state of Georgia. Has there been an increase in the occurrence of unusually above or below normal monthly temperatures in recent years? METHODOLOGY. Mean monthly temperatures for the period 19401982 for seven sites in Georgia plus the nearby locations ofChattanooga, TN, Tallahassee, FL, and Jacksonville, FL, were used for study (Fig. 1). The three non-Georgia stations were included to provide surrogate data for the far northern and southern regions ofthe state in the absence ofappropriate in-state sites. Monthly average temperature and standard deviation values for the 43-year period are given in Table 1. It is notable that winter months have much more temperature variability than summer months as indicated by consistently higher standard deviation values at all sites. In order to assess interannual changes in temperature variability, it is therefore appropriate to conduct the analysis on a month by month basis.
8. 1987: Suckling, Philip W. “A climate departure index for the study of climatic variability.” Physical Geography 8.2 (1987): 179-188. Three versions of a Climate Departure Index (CDI) are presented for studying how “normal” or “unusual” a particular year or event is compared to the long-term average for the region under consideration. Comparisons of a Simple CDI, Absolute Value CDI and Least-Squares CDI are made through the use of hypothetical examples and two case studies involving seasonal snowfall variations in northern New England and last spring-freeze date variations in the southeastern United States. Results clearly show that the Simple CDI is the inferior formulation owing to a compensation problem whereby above and below average sites within a region for a particular year cancel each other when computing the index value. Little difference in identifying extreme years was found between use of the Absolute Value CDI and Least-Squares CDI in the case studies examined. Nevertheless, a hypothetical example suggests that the least-squares approach for closeness of fit is the more appropriate method, thus making the Least-Squares CDI the preferred version.
9. 1992: Read, J. F., and W. J. Gould. “Cooling and freshening of the subpolar North Atlantic Ocean since the 1960s.” Nature360.6399 (1992): 55. LITTLE is known of the interdecadal variability in the thermohaline circulation of the world’s oceans, yet such knowledge is essential as a background to studies of the effects of natural and anthropogenic climate change. The subpolar North Atlantic is an area of extensive water mass modification by heat loss to the atmosphere. Lying as it does at the northern limit of the global thermohaline “conveyor belt”¹², changes in this region may ultimately have global consequences. Here we report that in August 1991 the waters between Greenland and the United Kingdom were on average 0.08 °C and 0.15 °C colder than in 1962 and 1981, respectively, and slightly less saline than in 1962. The cause appears to be renewed formation of intermediate water in the Labrador Sea from cooler and fresher source waters, and the spreading of this water mass from the west. Variations in the source characteristics of Labrador Sea Water can be traced across the North Atlantic, with a circulation time of 18–19 years between the Labrador Sea and Rockall Trough. More recently formed Labrador Sea Water, with even lower temperature and salinity, should cool and freshen the North Atlantic still further as it circulates around the ocean in the coming decade.
10. 2000: Andronova, Natalia G., and Michael E. Schlesinger. “Causes of global temperature changes during the 19th and 20th centuries.” Geophysical Research Letters 27.14 (2000): 2137-2140. During the past two decades there has been considerable discussion about the relative contribution of different factors to the temperature changes observed now over the past 142 years. Among these factors are the “external’ factors of human (anthropogenic) activity, volcanoes and putative variations in the irradiance of the sun, and the “internal” factor of natural variability. Here, by using a simple climate/ocean model to simulate the observed temperature changes for different state‐of‐the‐art radiative‐forcing models, we present strong evidence that while the anthropogenic effect has steadily increased in size during the entire 20th century such that it presently is the dominant external forcing of the climate system, there is a residual factor at work within the climate system, whether a natural oscillation or something else as yet unknown. This has an important implication for our expectation of future temperature changes.
11. 2008: Peterson, Thomas C., William M. Connolley, and John Fleck. “The myth of the 1970s global cooling scientific consensus.” Bulletin of the American Meteorological Society 89.9 (2008): 1325-1338. Climate science as we know it today did not exist in the 1960s and 1970s. The integrated enterprise embodied in the Nobel Prize winning work of the IPCC existed then as separate threads of research pursued by isolated groups of scientists. Atmospheric chemists and modelers grappled with the measurement of changes in carbon dioxide and atmospheric gases, and the changes in climate that might result. Meanwhile, geologists and paleoclimate researchers tried to understand when Earth slipped into and out of ice ages, and why. An enduring popular myth suggests that in the 1970s the climate science community was predicting “global cooling” and an “imminent” ice age, an observation frequently used by those who would undermine what climate scientists say today about the prospect of global warming. A review of the literature suggests that, on the contrary, greenhouse warming even then dominated scientists’ thinking as being one of the most important forces shaping Earth’s climate on human time scales. More importantly than showing the falsehood of the myth, this review describes how scientists of the time built the foundation on which the cohesive enterprise of modern climate science now rests. NOAA/National Climatic Data Center, Asheville
12. 2014: Hodson, Daniel LR, Jon I. Robson, and Rowan T. Sutton. “An anatomy of the cooling of the North Atlantic Ocean in the 1960s and 1970s.” Journal of Climate 27.21 (2014): 8229-8243. In the 1960s and early 1970s, sea surface temperatures in the North Atlantic Ocean cooled rapidly. There is still considerable uncertainty about the causes of this event, although various mechanisms have been proposed. In this observational study, it is demonstrated that the cooling proceeded in several distinct stages. Cool anomalies initially appeared in the mid-1960s in the Nordic Seas and Gulf Stream extension, before spreading to cover most of the subpolar gyre. Subsequently, cool anomalies spread into the tropical North Atlantic before retreating, in the late 1970s, back to the subpolar gyre. There is strong evidence that changes in atmospheric circulation, linked to a southward shift of the Atlantic ITCZ, played an important role in the event, particularly in the period 1972–76. Theories for the cooling event must account for its distinctive space–time evolution. The authors’ analysis suggests that the most likely drivers were 1) the “Great Salinity Anomaly” of the late 1960s; 2) an earlier warming of the subpolar North Atlantic, which may have led to a slowdown in the Atlantic meridional overturning circulation; and 3) an increase in anthropogenic sulfur dioxide emissions. Determining the relative importance of these factors is a key area for future work.

1940S-1970S COOLING GRAPHIC (FROM @ISABELLEAISIA )

Edit this entry.