Thongchai Thailand

The Ocean Heat Waves of AGW

Posted on: January 30, 2020

bandicam 2020-01-30 09-12-28-924


TRANSCRIPT {From 4:30 to 5:30 in the video}: Question: The IPCC report also describes the  relatively new phenomenon of MARINE HEAT WAVES in the ocean. Can you explain that to us? Answer: Well, marine heat waves have probably always occurred but they occurred naturally, but 90% of the marine heat waves over the past couple of decades are now attributable to humans – attributable to human caused climate change. So that’s a tremendous amount and they’re expecting that by the end of the century we could see them increase by 25 fold so a 25 times increase in the amount of marine heat waves is possible by the end of the century especially in a high emission scenario – when I say high emission scenario I mean business as usual – we keep burning lost of fossil fuels. So the bottom line is most of the heat waves in the ocean are being caused by us now and we are going to see them increase by 25 times??? So basically all the coral is going to die if we don’t do something to reel in all the fossil fuels that we are burning and all the greenhouse gases that we are releasing to the atmosphere.  {from here the discussion moves to sea level rise}. 










  1. As in the CBS News Climate Watch video cited above, the media often describes the Marine Heat Wave anomaly as a creation of ocean heat content gone awry and out of control or as impacts of “irreversible climate change”. In fact the so called Marine Heat Waves are localized evanescent SST anomalies. In other words they are well contained and limited in time and space.
  2. Figure 1 displays global mean SST 1979-2018 using UAH lower troposphere temperatures above the oceans and their decadal warming rates. Here we see that SST has been on a steady warming rate over the whole of the study period but the right frame of the chart shows that the decadal warming rates have varied over a large range that includes some very high warming rates and also some periods of cooling.
  3. Although SST is fairly uniform at any given time out in the open sea, anomalous SST is seen in ENSO events at specific locations where ENSO SST anomalies are known to occur; and similarly in the Indian Ocean Dipole. In addition to those SST anomalies in the open sea, MHW SST anomalies are also found in shallow waters near land and along continental shelves. These SST anomalies are thought to be related to shallowness and proximity to land as seen in the bibliography below.
  4. In these SST anomalies there can be significant departures from the mean ocean SST in both directions – hotter than average (marine heat wave or MHW) and colder than average (marine cold wave (MCW). See for example, Schlegel (2017) in the bibliography below. These anomalous SST “hotspots” can persist and hang around for days and even weeks. As a rule, these SST anomalies are classified as MHW only if they persist for 5 days or more  (See Hobday 2016 in the bibliography below).
  5. It is generally agreed that since these anomalies tend to occur in proximity to land that proximity to land may be a factor in the creation of these anomalies. Another location oddity of the MHW is that their location is not random but that they tend to be found in the same location over and over.
  6. Figure 2 above is a video display of MHW locations and intensity over time that begins in December 2018 and moves forward one month at a time all the way to January 2020. MHW locations are marked with color coded markers from yellow through orange, red, dark red, brown, and black. Intensity is proportional to the darkness of the color code of the MHW location – the darker the more intense. The video was created with data provided by These data do not include cold waves. is a a very useful resource in the study of MHW.
  7. As the video steps through time one month at a time we find that hardly any MWH lasts longer than a month. A notable exception is seen in the extreme NorthEast of Canada and in Northwest Greenland where a small cluster of MHW appears to persist for longer time periods. Also in the video, we see that the MHW locations month to month are not random but that MHW tends to recur in the same location over and over and at similar intensities. This behavior may imply that MHW is location specific. An apparent oddity of the spatial pattern of MHW events in this video is that most MHW SST anomalies tend to occur in polar regions both north and south. This pattern is stronger in the more intense SST anomalies.
  8. We find in this video and in the bibliography below, that locations of SST anomalies described as Marine Heat Waves do not follow a pattern that would imply a uniform atmospheric cause by way of fossil fuel driven AGW climate change as claimed in the CBS News Climate Watch video presented above and in many of the papers listed in the bibliography below. Significantly, not all papers claim a uniform atmospheric cause although most do eventually make the connection to AGW climate change.
  9. An oddity is that though the media presents MHW as a climate change horror in terms of irreversible climate change and the end of the ocean as we know it, and that “all the coral will die”, the bibliography does not. There are of course some impacts on ocean ecosystems in the MHW regions and these are described in the bibliography but they are localized and limited in time span. It is also of note than many of the papers ascribe these MHW events to known natural cyclical and localized temperature events such as the Indian Ocean Dipole and ENSO events.
  10. To that we should also add geological activity as a possible driver of these events because they are localized both in time and place, because they recur in the same location, and because of their prevalence in the geologically active polar regions in both the Arctic [LINK] and the Antarctic [LINK] .
  11. It is highly unlikely that these events are driven by fossil fuel emissions, that they can be moderated with climate action in the form of reducing or eliminating fossil fuel emissions; or that MHW will increase 25 fold by the year 2100 if we don’t take climate action. No evidence has been presented to relate these localized and evanescent SST anomalies to AGW climate change except that they have occurred during the AGW era. The attribution of these SST anomalies to AGW climate change and thereby to fossil fuel emissions appears to be arbitrary and a case of confirmation bias [LINK].
  12. A bibliography of MHW is included below. The research agenda appears to be mostly concerned with the impacts of MHW on the ocean’s ecosystem including impacts that may be relevant to humans as for example a degradation of fisheries.




  1. Zinke, Jens, et al. “Coral record of southeast Indian Ocean marine heatwaves with intensified Western Pacific temperature gradient.” Nature Communications 6.1 (2015): 1-9Increasing intensity of marine heatwaves has caused widespread mass coral bleaching events, threatening the integrity and functional diversity of coral reefs. Here we demonstrate the role of inter-ocean coupling in amplifying thermal stress on reefs in the poorly studied southeast Indian Ocean (SEIO), through a robust 215-year (1795–2010) geochemical coral proxy sea surface temperature (SST) record. We show that marine heatwaves affecting the SEIO are linked to the behaviour of the Western Pacific Warm Pool on decadal to centennial timescales, and are most pronounced when an anomalously strong zonal SST gradient between the western and central Pacific co-occurs with strong La Niña’s. This SST gradient forces large-scale changes in heat flux that exacerbate SEIO heatwaves. Better understanding of the zonal SST gradient in the Western Pacific is expected to improve projections of the frequency of extreme SEIO heatwaves and their ecological impacts on the important coral reef ecosystems off Western Australia. [FULL TEXT]
  2. Schlegel, Robert W., et al. “Nearshore and offshore co-occurrence of marine heatwaves and cold-spells.” Progress in oceanography 151 (2017): 189-205A changing global climate places shallow water ecosystems at more risk than those in the open ocean as their temperatures may change more rapidly and dramatically. To this end, it is necessary to identify the occurrence of extreme ocean temperature events – marine heatwaves (MHWs) and marine cold-spells (MCSs) – in the nearshore (<400 m from the coastline) environment as they can have lasting ecological effects. The occurrence of MHWs have been investigated regionally, but no investigations of MCSs have yet to be carried out. A recently developed framework that defines these events in a novel way was applied to ocean temperature time series from (i) a nearshore in situ dataset and (ii) 14° NOAA Optimally Interpolated sea surface temperatures. Regional drivers due to nearshore influences (local-scale) and the forcing of two offshore ocean currents (broad-scale) on MHWs and MCSs were taken into account when the events detected in these two datasets were used to infer the links between offshore and nearshore temperatures in time and space. We show that MHWs and MCSs occur at least once a year on average but that proportions of co-occurrence of events between the broad- and local scales are low (0.20–0.50), with MHWs having greater proportions of co-occurrence than MCSs. The low rates of co-occurrence between the nearshore and offshore datasets show that drivers other than mesoscale ocean temperatures play a role in the occurrence of at least half of nearshore events. Significant differences in the duration and intensity of events between different coastal sections may be attributed to the effects of the interaction of oceanographic processes offshore, as well as with local features of the coast. The decadal trends in the occurrence of MHWs and MCSs in the offshore dataset show that generally MHWs are increasing there while MCSs are decreasing. This study represents an important first step in the analysis of the dynamics of events in nearshore environments, and their relationship with broad-scale influences. [FULL TEXT PDF]
  3. Oliver, Eric CJ, et al. “Anthropogenic and natural influences on record 2016 marine heat waves.” Bulletin of the American Meteorological Society 99.1 (2018): S44-S48.  In 2016 a quarter of the ocean surface experienced either the longest or most intense marine heatwave (Hobday et al. 2016) since satellite records
    began in 1982. Here we investigate two regions Northern Australia (NA) and the Bering Sea/Gulf of Alaska (BSGA) which, in 2016, experienced their most intense marine heat waves (MHWs) in the 35-year record. The NA event triggered mass bleaching of corals in the Great Barrier Reef (Hughes et al. 2017) while the BSGA event likely fed back on the atmosphere leading to modified rainfall and temperature patterns over North America, and it is feared it may lead to widespread species range shifts as was observed during the “Blob” marine heat wave which occurred immediately to the south over 2013–15 (Belles 2016; Cavole et al. 2016). Moreover, from a climate perspective it is interesting to take examples
    from climate zones with very different oceanographic characteristics (high-latitude and tropics). We demonstrate that these events were several times more likely due to human influences on the climate. [FULL TEXT] {amsoc book: very large file}
  4. Scannell, Hillary A., et al. “Frequency of marine heatwaves in the North Atlantic and North Pacific since 1950.” Geophysical Research Letters 43.5 (2016): 2069-2076.  Extreme and large‐scale warming events in the ocean have been dubbed marine heatwaves, and these have been documented in both the Northern and Southern Hemispheres. This paper examines the intensity, duration, and frequency of positive sea surface temperature anomalies in the North Atlantic and North Pacific Oceans over the period 1950–2014 using an objective definition for marine heatwaves based on their probability of occurrence. Small‐area anomalies occur more frequently than large‐area anomalies, and this relationship can be characterized by a power law distribution. The relative frequency of large‐ versus small‐area anomalies, represented by the power law slope parameter, is modulated by basin‐scale modes of natural climate variability and anthropogenic warming. Findings suggest that the probability of marine heatwaves is a trade‐off between size, intensity, and duration and that region specific variability modulates the frequency of these events. [FULL TEXT]  
  5. Hobday, Alistair J., et al. “A hierarchical approach to defining marine heatwaves.” Progress in Oceanography 141 (2016): 227-238Marine heatwaves (MHWs) have been observed around the world and are expected to increase in intensity and frequency under anthropogenic climate change. A variety of impacts have been associated with these anomalous events, including shifts in species ranges, local extinctions and economic impacts on seafood industries through declines in important fishery species and impacts on aquaculture. Extreme temperatures are increasingly seen as important influences on biological systems, yet a consistent definition of MHWs does not exist. A clear definition will facilitate retrospective comparisons between MHWs, enabling the synthesis and a mechanistic understanding of the role of MHWs in marine ecosystems. Building on research into atmospheric heatwaves, we propose both a general and specific definition for MHWs, based on a hierarchy of metrics that allow for different data sets to be used in identifying MHWs. {PROPOSED DEFINITION: We define a MHW as a prolonged discrete anomalously warm water event that can be described by its duration, intensity, rate of evolution, and spatial extent and if it lasts for five or more days, with temperatures warmer than the 90th percentile based on a 30-year history}. This structure provides flexibility with regard to the description of MHWs and transparency in communicating MHWs to a general audience. The use of these metrics is illustrated for three 21st century MHWs; the northern Mediterranean event in 2003, the Western Australia ‘Ningaloo Niño’ in 2011, and the northwest Atlantic event in 2012. We recommend a specific quantitative definition for MHWs to facilitate global comparisons and to advance our understanding of these phenomena.
  6. Frölicher, Thomas L., Erich M. Fischer, and Nicolas Gruber. “Marine heatwaves under global warming.” Nature 560.7718 (2018): 360-364Marine heatwaves (MHWs) are periods of extreme warm sea surface temperature that persist for days to months1 and can extend up to thousands of kilometres2. Some of the recently observed marine heatwaves revealed the high vulnerability of marine ecosystems3,4,5,6,7,8,9,10,11 and fisheries12,13,14 to such extreme climate events. Yet our knowledge about past occurrences15 and the future progression of MHWs is very limited. Here we use satellite observations and a suite of Earth system model simulations to show that MHWs have already become longer-lasting and more frequent, extensive and intense in the past few decades, and that this trend will accelerate under further global warming. Between 1982 and 2016, we detect a doubling in the number of MHW days, and this number is projected to further increase on average by a factor of 16 for global warming of 1.5 degrees Celsius relative to preindustrial levels and by a factor of 23 for global warming of 2.0 degrees Celsius. However, current national policies for the reduction of global carbon emissions are predicted to result in global warming of about 3.5 degrees Celsius by the end of the twenty-first century16, for which models project an average increase in the probability of MHWs by a factor of 41. At this level of warming, MHWs have an average spatial extent that is 21 times bigger than in preindustrial times, last on average 112 days and reach maximum sea surface temperature anomaly intensities of 2.5 degrees Celsius. The largest changes are projected to occur in the western tropical Pacific and Arctic oceans. Today, 87 per cent of MHWs are attributable to human-induced warming, with this ratio increasing to nearly 100 per cent under any global warming scenario exceeding 2 degrees Celsius. Our results suggest that MHWs will become very frequent and extreme under global warming, probably pushing marine organisms and ecosystems to the limits of their resilience and even beyond, which could cause irreversible changes.
  7. Hobday, Alistair J., et al. “Categorizing and naming marine heatwaves.” Oceanography 31.2 (2018): 162-173.. Considerable attention has been directed at understanding the consequences and impacts of long-term anthropogenic climate change. Discrete, climatically extreme events such as cyclones, floods, and heatwaves can also significantly affect regional environments and species, including humans. Climate change is expected to intensify these events and thus exacerbate their effects. Climatic extremes also occur in the ocean, and recent decades have seen many high-impact marine heatwaves (MHWs) anomalously warm water events that may last many months and extend over thousands of square kilometers. A range of biological, economic, and political impacts have been associated with the more intense MHWs, and measuring the severity of these phenomena is becoming more important. Progress in understanding and public awareness will be facilitated by consistent description of these events. Here, we propose a detailed categorization scheme for MHWs that builds on a recently published classification, combining elements from schemes that describe atmospheric heatwaves and hurricanes. Category I, II, III, and IV MHWs are defined based on the degree to which temperatures exceed the local climatology and illustrated for 10 MHWs. While there is a long-term increase in the occurrence frequency of all MHW categories, the largest trend is a 24% increase in the area of the ocean where strong (Category II) MHWs occur. Use of this scheme can help explain why biological impacts associated with different MHWs can vary widely and provides a consistent way to compare events. We also propose a simple naming convention based on geography and year that would further enhance scientific and public awareness of these marine events. [FULL TEXT] .
  8. Oliver, Eric CJ, et al. “Longer and more frequent marine heatwaves over the past century.” Nature communications 9.1 (2018): 1-12.  Heatwaves are important climatic extremes in atmospheric and oceanic systems that can have devastating and long-term impacts on ecosystems, with subsequent socioeconomic consequences. Recent prominent marine heatwaves have attracted considerable scientific and public interest. Despite this, a comprehensive assessment of how these ocean temperature extremes have been changing globally is missing. Using a range of ocean temperature data including global records of daily satellite observations, daily in situ measurements and gridded monthly in situ-based data sets, we identify significant increases in marine heatwaves over the past century. We find that from 1925 to 2016, global average marine heatwave frequency and duration increased by 34% and 17%, respectively, resulting in a 54% increase in annual marine heatwave days globally. Importantly, these trends can largely be explained by increases in mean ocean temperatures, suggesting that we can expect further increases in marine heatwave days under continued global warming. [[FULL TEXT] {Blogger’s Translation: from 1925 to 2016 ocean temperature has been rising and that rise is ascribed to AGW; and at the same time marine heat waves have also been rising so therefore marine heat waves must also be caused by AGW}.
  9. Smale, Dan A., et al. “Marine heatwaves threaten global biodiversity and the provision of ecosystem services.” Nature Climate Change 9.4 (2019): 306-312.  The global ocean has warmed substantially over the past century, with far-reaching implications for marine ecosystems1. Concurrent with long-term persistent warming, discrete periods of extreme regional ocean warming (marine heatwaves, MHWs) have increased in frequency2. Here we quantify trends and attributes of MHWs across all ocean basins and examine their biological impacts from species to ecosystems. Multiple regions in the Pacific, Atlantic and Indian Oceans are particularly vulnerable to MHW intensification, due to the co-existence of high levels of biodiversity, a prevalence of species found at their warm range edges or concurrent non-climatic human impacts. The physical attributes of prominent MHWs varied considerably, but all had deleterious impacts across a range of biological processes and taxa, including critical foundation species (corals, seagrasses and kelps). MHWs, which will probably intensify with anthropogenic climate change3, are rapidly emerging as forceful agents of disturbance with the capacity to restructure entire ecosystems and disrupt the provision of ecological goods and services in coming decades.
  10. MARINE HEAT WAVES DOT ORG:  We know that heatwaves occur in the atmosphere. We are all familiar with these extended periods of excessively hot weather. However, heatwaves can also occur in the ocean and these are known as marine heatwaves, or MHWs. These marine heatwaves, when ocean temperatures are extremely warm for an extended period of time can have significant impacts on marine ecosystems and industries.​ Marine heatwaves can occur in summer or winter – they are defined based on differences with expected temperatures for the location and time of year. We use a recently developed definition of marine heatwaves (Hobday et al. 2016). A marine heatwave is defined a when seawater temperatures exceed a seasonally-varying threshold (usually the 90th percentile) for at least 5 consecutive days. Successive heatwaves with gaps of 2 days or less are considered part of the same event.
  11. MARINE HEAT WAVE TRACKER: [LINK] This web application shows up to date information on where in the world marine heatwaves (MHWs) are occurring and what category they are.


6 Responses to "The Ocean Heat Waves of AGW"

[…] Marine heat waves are described in some detail in a related post [LINK] Marine heat waves are not really heat waves but a temporary SST (sea surface temperature) anomaly […]

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