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Stratospheric Cooling

Posted on: August 22, 2018

 

stratos4

 

FIGURE 1: GLOBAL TEMP: WARMING TROPOSPHERE, COOLING STRATOSPHERE

TROP-STRAT-CORR

 

FIGURE 2: GLOBAL TEMP: CORRELATION WITH LN(CO2)

TROP-STRAT-CO2-CORR

 

FIGURE 3: TYLER VIGEN SPURIOUS CORRELATION DEMONSTRATION

Spurious_Correlation

 

FIGURE 4: THE RATIONALE FOR DETRENDED CORRELATION ANALYSIS

 

 

FIGURE 5: DETRENDED ANALYSIS: RESPONSIVENESS OF STRATOSPHERIC COOLING TO TROPOSPHERIC WARMING AT AN ANNUAL TIME SCALE

DET-TROP-STRAT

 

FIGURE 6: DETRENDED CORRELATION: LN(ATMOS-CO2) AND TROPOSPHERIC AND STRATOSPHERIC TEMPERATURE 1979-2017

DETCORRP-TEMP-CO2

 

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The literature review presented below describes results of a large number of climate model simulations of atmospheric conditions under an artificial increase in carbon dioxide concentration. Their unanimous conclusion is that such artificial forcing will cause warming of the troposphere, popularly known as global warming and climate change by way of the heat trapping effect of carbon dioxide. Less well known is that the model simulations also describe the effect of these changes on the stratosphere. In particular, the models show a cooling of the lower stratosphere. It is thought that the partial shielding of the stratosphere from long wave surface radiation due to CO2 absorption causes the stratosphere to cool.

These trends are found in the observational data. Since 1979 microwave sounding units (MSUs) on National Oceanic and Atmospheric Administration polar orbiting satellites have been recording accurate measures of zonal atmospheric temperatures at various elevations in both the troposphere and the stratosphere. Figure 1 above contains three panels that depict satellite temperature anomaly data for the sample period 1979-2017 supplied by the University of Alabama, Huntsville (UAH) available online at Christy/Spencer 2018The left panel shows the lower troposphere is warming. OLS linear regression shows a very high average warming rate 1.29C/century. The middle panel shows that the corresponding temperature anomalies in the lower stratosphere are in a downward trend with a high average OLS cooling rate of -2.96C/century. This pattern of warming troposphere and cooling stratosphere is exactly what the model simulations listed below have predicted. The right panel of Figure 1 appears to indicate that these two opposing trends are synchronized by way of a statistically significant negative correlation r=-0.60.

The theoretical causal connection between synchronized tropospheric warming and stratospheric cooling seen in the climate models is rising atmospheric carbon dioxide. The theoretical relationship and rationale for these changes built into the climate models is that the temperature in both of these layers of the atmosphere is driven by atmospheric carbon dioxide concentration in terms of a theoretical linear relationship between the logarithm of carbon dioxide concentration and temperature. These relationships are shown in Figure 2.

The middle panel of Figure 2 shows a strong positive correlation between log(CO2) and tropospheric temperature in terms of a strong correlation of r=0.72. The positive sign of the correlation is consistent with the theoretical relationship in which CO2 causes troposphere temperature to rise. The right panel of Figure 2 shows a strong negative correlation between log(CO2) and lower stratospheric temperature in terms of a strong correlation of r=-0.76. The negative sign of the correlation is consistent with the theoretical relationship in which CO2 causes lower stratospheric temperature to fall.

However, there are some statistical considerations that require caution in the interpretation of time series data, particularly field data taken as given and not under a controlled experiment. This issue is discussed at length in a related post on SPURIOUS CORRELATIONS IN CLIMATE SCIENCE

In short, correlations between time series of field data require extreme caution to separate out and remove the effect of long term trends so that the theoretical responsiveness at a given time scale may be assessed. Failure to do so results in the kind of comical conclusions demonstrated by Tyler Vigen in his excellent statistics site  TYLERVIGEN SPURIOUS CORRELATION DEMONSTRATIONS An example from the large Tyler Vigen collection is shown in Figure 3. These spurious correlations demonstrate that shared trends can create a faux correlation that is unrelated to responsiveness at the time scale of interest. Long term trends have a time scale equal to the full span with a sample size of one, no degrees of freedom, and no statistical power. his issue is discussed in a Youtube video lecture by Alex Tolley (Link:  ALEX TOLLEY’S LECTURE  . A small portion of the video appears above in Figure 4.

The inverse correlation of r=-0.60 between tropospheric warming and stratospheric cooling shown in Figure 1 is tested with detrended correlation analysis for responsiveness at an annual time scale in Figure 5. No statistically significant correlation is found. The observed correlation has dropped from r=-0.60 in the source data to r=-0.08 in the detrended data indicating that the high source data correlation is an artifact of shared trends and not an indication of responsiveness at an annual time scale.

Figure 6 displays the results of detrended correlation analysis for the responsiveness of of the two atmospheric temperature series to changes in LN(CO2) at an annual time scale net of long term trends. Here we find that the strong correlation seen in the source data of r = +0.72 in tropospheric temperature and r = -0.76 in lower stratospheric temperature do not survive into the detrended data and are therefore spurious artifacts of long term trends and do not indicators of responsiveness at an annual time scale. For the tropospheric temperature series, the correlation drops to a near zero and statistically insignificant value of r = +0.15 and for the lower stratosphere the correlation flips sign over to a positive value of r = +0.385. Since these are one-sided hypothesis tests where we expect r>0 for tropospheric temperatures and r<0 for stratospheric temperatures, we are unable to reject the null hypothesis in either case.

We conclude that no evidence is found in the observational data to indicate that either tropospheric warming or lower stratospheric cooling is responsive to changes in LN(CO2) or that stratospheric cooling is responsive to tropospheric warming, at an annual time scale. These data do not support the theory of causation that links tropospheric warming or stratospheric cooling to atmospheric CO2.

 

 

 

 

 

BIBLIOGRAPHY

  1. 1975: Manabe, Syukuro, and Richard T. Wetherald. “The effects of doubling the CO2 concentration on the climate of a general circulation model.” Journal of the Atmospheric Sciences 32.1 (1975): 3-15. An attempt is made to estimate the temperature changes resulting from doubling the present CO2concentration by the use of a simplified three-dimensional general circulation model. This model contains the following simplications: a limited computational domain, an idealized topography, no beat transport by ocean currents, and fixed cloudiness. Despite these limitations, the results from this computation yield some indication of how the increase of CO2 concentration may affect the distribution of temperature in the atmosphere. It is shown that the CO2 increase raises the temperature of the model troposphere, whereas it lowers that of the model stratosphere. The tropospheric warming is somewhat larger than that expected from a radiative-convective equilibrium model. In particular, the increase of surface temperature in higher latitudes is magnified due to the recession of the snow boundary and the thermal stability of the lower troposphere which limits convective heating to the lowest layer. It is also shown that the doubling of carbon dioxide significantly increases the intensity of the hydrologic cycle of the model.
  2. 1988: Ramanathan, Veerabhachan. “The greenhouse theory of climate change: a test by an inadvertent global experiment.” Science 240.4850 (1988): 293-299. Since the dawn of the industrial era, the atmospheric concentrations of several radiatively active gases have been increasing as a result of human activities. The radiative heating from this inadvertent experiment has driven the climate system out of equilibrium with the incoming solar energy. According to the greenhouse theory of climate change, the climate system will be restored to equilibrium by a warming of the surfacetroposphere system and a cooling of the stratosphere. The predicted changes, during the next few decades, could far exceed natural climate variations in historical times. Hence, the greenhouse theory of climate change has reached the crucial stage of verification. Surface warming as large as that predicted by models would be unprecedented during an interglacial period such as the present. The theory, its scope for verification, and the emerging complexities of the climate feedback mechanisms are discussed.
  3. 1989: Washington, Warren M., and Gerald A. Meehl. “Climate sensitivity due to increased CO 2: experiments with a coupled atmosphere and ocean general circulation model.” Climate dynamics 4.1 (1989): 1-38. A version of the National Center for Atmospheric Research community climate model — a global, spectral (R15) general circulation model — is coupled to a coarse-grid (5° latitude-] longitude, four-layer) ocean general circulation model to study the response of the climate system to increases of atmospheric carbon dioxide (CO2). Three simulations are run: one with an instantaneous doubling of atmospheric CO2 (from 330 to 660 ppm), another with the CO2concentration starting at 330 ppm and increasing linearly at a rate of 1% per year, and a third with CO2 held constant at 330 pm. Results at the end of 30 years of simulation indicate a globally averaged surface air temperature increase of 1.6° C for the instantaneous doubling case and 0.7°C for the transient forcing case. Inherent characteristics of the coarse-grid ocean model flow sea-surface temperatures (SSTs) in the tropics and higher-than-observed SSTs and reduced sea-ice extent at higher latitudes] produce lower sensitivity in this model after 30 years than in earlier simulations with the same atmosphere coupled to a 50-m, slab-ocean mixed layer. Within the limitations of the simulated meridional overturning, the thermohaline circulation weakens in the coupled model with doubled CO2 as the high-latitude ocean-surface layer warms and freshens and westerly wind stress is decreased. In the transient forcing case with slowly increasing CO2 (30% increase after 30 years), the zonal mean warming of the ocean is most evident in the surface layer near 30°–50° S. Geographical plots of surface air temperature change in the transient case show patterns of regional climate anomalies that differ from those in the instantaneous CO2 doubling case, particularly in the North Atlantic and northern European regions. This suggests that differences in CO2 forcing in the climate system are important in CO2 response in regard to time-dependent climate anomaly regimes. This confirms earlier studies with simple climate models that instantaneous CO2 doubling simulations may not be analogous in all respects to simulations with slowly increasing CO2
  4. 1990: Rind, D., et al. “Climate change and the middle atmosphere. Part I: The doubled CO2 climate.” Journal of the Atmospheric Sciences 47.4 (1990): 475-494.The impact of doubled atmospheric CO2 on the climate of the middle atmosphere is investigated using the GISS global climate/middle atmosphere model. In the standard experiment, the CO2 concentration is doubled both in the stratosphere and troposphere, and the sea surface temperatures are increased to match those of the doubled CO2 run of the GISS 9 level climate model. Additional experiments are run to determine how the middle atmospheric effects are influenced by tropospheric changes, and to separate the dynamic and radiative influences. These include the use of the greater high latitude/low latitude surface warming ratio generated by the Geophysical Fluid Dynamics Laboratory doubled CO2experiments, doubling the CO2 only in either the troposphere or stratosphere, and allowing the middle atmosphere to react only radiatively. As expected, doubled CO2 produces warmer temperatures in the troposphere, and generally cooler temperatures in the stratosphere. The net result is a decrease of static stability for the atmosphere as a whole. In addition, the 100 mb warming maximizes in the tropics, leading to improved propagation conditions for planetary waves, and increased potential energy in the lower stratosphere. These processes generate increased eddy energy in the middle atmosphere in most seasons. With greater eddy energy comes greater eddy forcing of the mean flow and an increase in the intensity of the residual circulation from the equator to the pole, which tends to warm high latitudes. Increased gravity wave drag in some of the experiments also helps to intensify the circulation. The middle atmosphere dynamical differences are on the order of 10%–20% of the model values for the current climate, and, along with the calculated temperature differences of up to some 10°C, may have a significant impact on the chemistry of the future atmosphere including that of stratospheric ozone, the polar ozone “hole,” and basic atmospheric composition.
  5. 1992: Pitari, G., et al. “Ozone response to a CO2 doubling: Results from a stratospheric circulation model with heterogeneous chemistry.” Journal of Geophysical Research: Atmospheres97.D5 (1992): 5953-5962. A spectral three‐dimensional model of the stratosphere has been used to study the sensitivity of polar ozone with respect to a carbon dioxide increase. The lower stratospheric cooling associated with an imposed CO2 doubling may increase the probability of polar stratospheric cloud (PSC) formation and thus affect ozone. We compare the ozone perturbation obtained with the inclusion of a simple parameterization for heterogeneous chemistry on PSCs to that relative to a pure homogeneous chemistry. In both cases the temperature perturbation is determined by a CO2 doubling, while the total chlorine content is kept at the present level. It is shown that the lower temperature may increase the depth and the extension of the ozone hole by extending the area amenable to PSC formation. It may be argued that this effect, coupled with an increasing amount of chlorine, may produce a positive feedback on the ozone destruction.
  6. 1998: Danilin, Michael Y., et al. “Stratospheric cooling and Arctic ozone recovery.” Geophysical research letters 25.12 (1998): 2141-2144. We present sensitivity studies using the AER box model for an idealized parcel in the lower stratosphere at 70°N during winter/spring with different assumed stratospheric coolings and chlorine loadings. Our calculations show that stratospheric cooling could further deplete ozone via increased polar stratospheric cloud (PSC) formation and retard its expected recovery even with the projected chlorine loading decrease. We introduce the concept of chlorine‐cooling equivalent and show that a 1 K cooling could provide the same local ozone depletion as an increase of chlorine by 0.4–0.7 ppbv for the scenarios considered. Thus, sustained stratospheric cooling could further reduce Arctic ozone content and delay the anticipated ozone recovery in the Northern Hemisphere even with the realization of the Montreal Protocol and its Amendments.
  7. 1998: Rosenfield, Joan E., and Anne R. Douglass. “Doubled CO2 effects on NOy in a coupled 2D model.” Geophysical research letters 25.23 (1998): 4381-4384. Stratospheric NOy fields calculated using a zonally averaged interactive chemistry‐radiation‐dynamics model show significant sensitivity to the model CO2. Modeled upper stratospheric NOy decreases by about 15% in response to CO2 doubling, mainly due to the temperature decrease calculated to result from increased CO2 cooling. The abundance of atomic nitrogen, N, increases because the rate of the strongly temperature dependent reaction N + O2 → NO + O decreases at lower temperatures. Increased N leads to an increase in the loss of NOy which is controlled by the reaction N + NO → N2 + O. The decrease in NOy due to the lowered temperatures is partially compensated by changes in the residual circulation. In addition, the NOy reduction is shown to be sensitive to the NO photolysis rate.
  8. 1998: Rind, D., et al. “Climate change and the middle atmosphere. Part III: The doubled CO2 climate revisited.” Journal of Climate 11.5 (1998): 876-894. The response of the troposphere–stratosphere system to doubled atmospheric CO2 is investigated in a series of experiments in which sea surface temperatures are allowed to adjust to radiation imbalances. The Goddard Institute for Space Studies (GISS) Global Climate Middle Atmosphere Model (GCMAM) warms by 5.1°C at the surface while the stratosphere cools by up to 10°C. When ozone is allowed to respond photochemically, the stratospheric cooling is reduced by 20%, with little effect in the troposphere. Planetary wave energy increases in the stratosphere, producing dynamical warming at high latitudes, in agreement with previous GCMAM doubled CO2 simulations; the effect is due to increased tropospheric generation and altered refraction, both strongly influenced by the magnitude of warming in the model’s tropical upper troposphere. This warming also results in stronger zonal winds in the lower stratosphere, which appears to reduce stratospheric planetary wave 2 energy and stratospheric warming events. The dynamical changes in the lower stratosphere are weakened when O3 chemistry on polar stratospheric cloud effects are included at current stratospheric chlorine levels. Comparison with the nine-level version of the GISS GCM with a top at 10 mb shows that both the stratospheric and tropospheric dynamical responses are different. The tropospheric effect is mostly a function of the vertical resolution in the troposphere; finer vertical resolution leads to increased latent heat release in the warmer climate, greater zonal available potential energy increase, and greater planetary longwave energy and energy transports. The increase in planetary longwave energy and residual circulation in the stratosphere is reproduced when the model top is lifted from 30 to 50 km, which also affects upper-tropospheric stability, convection and cloud cover, and climate sensitivity.
  9. 1998: Dameris, M., et al. “Assessment of the future development of the ozone layer.” Geophysical Research Letters 25.19 (1998): 3579-3582.
  10. 1999: de F. Forster, Piers M., and Keith P. Shine. “Stratospheric water vapour changes as a possible contributor to observed stratospheric cooling.” Geophysical research letters 26.21 (1999): 3309-3312. The observed cooling of the lower stratosphere over the last two decades has been attributed, in previous studies, largely to a combination of stratospheric ozone loss and carbon dioxide increase, and as such it is meant to provide one of the best pieces of evidence for an anthropogenic cause to climate change. This study shows how increases in stratospheric water vapour, inferred from available observations, may be capable of causing as much of the observed cooling as ozone loss does; as the reasons for the stratospheric water vapour increase are neither fully understood nor well characterized, it shows that it remains uncertain whether the cooling of the lower stratosphere can yet be fully attributable to human influences. In addition, the changes in stratospheric water vapour may have contributed, since 1980, a radiative forcing which enhances that due to carbon dioxide alone by 40%.
  11. 2003: Gillett, N. P., M. R. Allen, and K. D. Williams. “Modelling the atmospheric response to doubled CO2 and depleted stratospheric ozone using a stratosphere‐resolving coupled GCM.” Quarterly Journal of the Royal Meteorological Society129.589 (2003): 947-966. We investigate the atmospheric response to doubled CO2 and stratospheric ozone depletion in three versions of a general‐circulation model with differing vertical resolution and upper‐boundary heights. We find that an approximate doubling of the vertical resolution below 10 hPa reduces the temperature response to a doubling of CO2from 3.4 K to 2.5 K. Much of this difference is associated with changes in the cloud response. All model versions show an increase in the Arctic Oscillation index in response to a doubling of CO2, but the increase is no larger in the model with an upper boundary at 0.01 hPa than in the standard model with a top level at 5 hPa. All models also show general stratospheric cooling in response to doubling CO2. However, unlike some other authors, we find no cooling in the Arctic winter vortex below around 10 hPa in the stratosphere‐resolving model, and a weakening of the zonal winds throughout this region. This effect is due to enhanced upward propagation of planetary waves from the troposphere, and is an effect found only in the northern hemisphere, probably because of its larger zonal asymmetries. All models show a small but significant surface cooling in response to a reconstruction of 1998 stratospheric ozone depletion, and an increase in the Antarctic Oscillation index in the southern summer. The cooling extends through most of the atmosphere, and reaches a maximum in the region of the Antarctic ozone hole in November and December. © Royal Meteorological Society, 2003. K. D. Williams’s contribution is Crown copyright.
  12. 2003: Langematz, Ulrike, et al. “Thermal and dynamical changes of the stratosphere since 1979 and their link to ozone and CO2 changes.” Journal of Geophysical Research: Atmospheres108.D1 (2003): ACL-9.  This study examines which part of the observed stratospheric thermal and dynamical changes since 1979 can be attributed to the observed stratospheric ozone (O3) losses and CO2 increases. Further, the processes are studied that lead to temperature and circulation changes when stratospheric O3 and CO2 are modified. We compared results from simulations of the Freie Universität Berlin Climate Middle Atmosphere Model (FUB CMAM) using observed O3 and CO2 changes with observed trends of stratospheric temperature and circulation for the period 1979–2000 from FUB data and National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalyses. The observed O3 decrease leads in the FUB CMAM to a global mean stratospheric cooling, which is enhanced in the upper stratosphere by the imposed CO2 increase. While the model is able to reproduce the observed stratospheric cooling in the upper stratosphere, it underestimates the observed trends in the lower stratosphere, particularly in middle latitudes and during Northern Hemisphere (NH) spring. The observed intensification and increased lifetimes of the polar vortices in spring are captured by the model but with smaller magnitude than observed. It is suggested that the observed upper stratospheric temperature trends during the past two decades in low to middle latitudes are caused by radiative effects due to the O3 and CO2 changes, while the cooling of the polar stratosphere in winter is enhanced by changes in dynamical heating. However, in northern midlatitudes and in Arctic spring, other effects than O3 and CO2 changes must be considered to fully explain the observed changes in the lower stratosphere.
  13. 2004: Sigmond, M., et al. “A simulation of the separate climate effects of middle-atmospheric and tropospheric CO2 doubling.” Journal of Climate 17.12 (2004): 2352-2367. The separate climate effects of middle-atmospheric and tropospheric CO2 doubling have been simulated and analyzed with the ECHAM middle-atmosphere climate model. To this end, the CO2 concentration has been separately doubled in the middle-atmosphere, the troposphere, and the entire atmosphere, and the results have been compared to a control run. During NH winter, the simulated uniformly doubled CO2 climate shows an increase of the stratospheric residual circulation, a small warming in the Arctic lower stratosphere, a weakening of the zonal winds in the Arctic middle-atmosphere, an increase of the NH midlatitude tropospheric westerlies, and a poleward shift of the SH tropospheric westerlies. The uniformly doubled CO2 response in most regions is approximately equal to the sum of the separate responses to tropospheric and middle-atmospheric CO2 doubling. The increase of the stratospheric residual circulation can be attributed for about two-thirds to the tropospheric CO2 doubling and one-third to the middle-atmospheric CO2 doubling. This increase contributes to the Arctic lower-stratospheric warming and, through the thermal wind relationship, to the weakening of the Arctic middle-atmospheric zonal wind. The increase of the tropospheric NH midlatitude westerlies can be attributed mainly to the middle-atmospheric CO2 doubling, indicating the crucial importance of the middle-atmospheric CO2 doubling for the tropospheric climate change. Results from an additional experiment show that the CO2 doubling above 10 hPa, which is above the top of many current GCMs, also causes significant changes in the tropospheric climate.
  14. 2006: Schmidt, H., et al. “The HAMMONIA chemistry climate model: Sensitivity of the mesopause region to the 11-year solar cycle and CO2 doubling.” Journal of Climate 19.16 (2006): 3903-3931. This paper introduces the three-dimensional Hamburg Model of the Neutral and Ionized Atmosphere (HAMMONIA), which treats atmospheric dynamics, radiation, and chemistry interactively for the height range from the earth’s surface to the thermosphere (approximately 250 km). It is based on the latest version of the ECHAM atmospheric general circulation model of the Max Planck Institute for Meteorology in Hamburg, Germany, which is extended to include important radiative and dynamical processes of the upper atmosphere and is coupled to a chemistry module containing 48 compounds. The model is applied to study the effects of natural and anthropogenic climate forcing on the atmosphere, represented, on the one hand, by the 11-yr solar cycle and, on the other hand, by a doubling of the present-day concentration of carbon dioxide. The numerical experiments are analyzed with the focus on the effects on temperature and chemical composition in the mesopause region. Results include a temperature response to the solar cycle by 2 to 10 K in the mesopause region with the largest values occurring slightly above the summer mesopause. Ozone in the secondary maximum increases by up to 20% for solar maximum conditions. Changes in winds are in general small. In the case of a doubling of carbon dioxide the simulation indicates a cooling of the atmosphere everywhere above the tropopause but by the smallest values around the mesopause. It is shown that the temperature response up to the mesopause is strongly influenced by changes in dynamics. During Northern Hemisphere summer, dynamical processes alone would lead to an almost global warming of up to 3 K in the uppermost mesosphere.
  15. 2007: Fomichev, V. I., et al. “Response of the middle atmosphere to CO2 doubling: Results from the Canadian Middle Atmosphere Model.” Journal of Climate 20.7 (2007): 1121-1144. The Canadian Middle Atmosphere Model (CMAM) has been used to examine the middle atmosphere response to CO2 doubling. The radiative-photochemical response induced by doubling CO2 alone and the response produced by changes in prescribed SSTs are found to be approximately additive, with the former effect dominating throughout the middle atmosphere. The paper discusses the overall response, with emphasis on the effects of SST changes, which allow a tropospheric response to the CO2 forcing. The overall response is a cooling of the middle atmosphere accompanied by significant increases in the ozone and water vapor abundances. The ozone radiative feedback occurs through both an increase in solar heating and a decrease in infrared cooling, with the latter accounting for up to 15% of the total effect. Changes in global mean water vapor cooling are negligible above ∼30 hPa. Near the polar summer mesopause, the temperature response is weak and not statistically significant. The main effects of SST changes are a warmer troposphere, a warmer and higher tropopause, cell-like structures of heating and cooling at low and middlelatitudes in the middle atmosphere, warming in the summer mesosphere, water vapor increase throughout the domain, and O3 decrease in the lower tropical stratosphere. No noticeable change in upward-propagating planetary wave activity in the extratropical winter–spring stratosphere and no significant temperature response in the polar winter–spring stratosphere have been detected. Increased upwelling in the tropical stratosphere has been found to be linked to changed wave driving at low latitudes.
  16. 2018: Smith, Karen L., et al. “No Surface Cooling over Antarctica from the Negative Greenhouse Effect Associated with Instantaneous Quadrupling of CO2 Concentrations.” Journal of Climate 31.1 (2018): 317-323. Over the highest elevations of Antarctica, during many months of the year, air near the surface is colder than in much of the overlying atmosphere. This unique feature of the Antarctic atmosphere has been shown to result in a negative greenhouse effect and a negative instantaneous radiative forcing at the top of the atmosphere , when carbon dioxide (CO2) concentrations are increased, and it has been suggested that this effect might play some role in the recent cooling trends observed over East Antarctica. Here, using fully coupled global climate model integrations, in addition to radiative transfer model calculations, the authors confirm the existence of such a negative  over parts of Antarctica in response to an instantaneous quadrupling of CO2. However, it is also shown that the instantaneous radiative forcing at the tropopause  is positive. Further, the negative  lasts only a few days following the imposed perturbation, and rapidly disappears as the stratosphere cools in response to increased CO2. As a consequence, like the , the stratosphere-adjusted radiative forcing at the TOA is positive over all of Antarctica and, in the model presented herein, surface temperatures increase everywhere over that continent in response to quadrupled CO2. The results, therefore, clearly demonstrate that the curious negative instantaneous radiative forcing plays no role in the recently observed East Antarctic cooling.

 

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