According to a recently published paper in the journal Science, (Cook et al., 2016, “Ocean forcing of glacier retreat in the western Antarctic Peninsula”), between 1945 and 2009 the mean ocean temperature warmed at depths of 150 to 400 meters for about 3/4ths of the waters surrounding the western Antarctic Peninsula (AP). The other 1/4th of the ocean waters at those depths (150 to 400 m) cooled (by -1°C ) during those 65 years.
As the authors point out, and as the graph above shows, in the areas where the waters warmed (light red shaded), glacier retreat was observed to be most pronounced (blood red points). In the regions (Bransfield Strait) where the ocean waters cooled (blue shaded), glaciers were in balance and even advanced (blue points). Citing this strong correlation between regional ocean warming/cooling and regional glacier retreat/advance, the authors concluded that the long-held assumption that atmospheric and surface warming (presumably driven by greenhouse gases) was what primarily caused Antarctic glaciers to recede is not supported by the evidence. Instead, it is the temperature of the ocean waters that “have been the predominant control on multidecadal glacier front behavior in the western AP.”
“Here, we identify a strong correspondence between mid-depth ocean temperatures and glacier-front changes along the ~1000-kilometer western coastline. In the south, glaciers that terminate in warm Circumpolar Deep Water have undergone considerable retreat, whereas those in the far northwest, which terminate in cooler waters, have not. Furthermore, a mid-ocean warming since the 1990s in the south is coincident with widespread acceleration of glacier retreat. We conclude that changes in ocean-induced melting are the primary cause of retreat for glaciers in this region. … [S]everal recent studies of Arctic glaciers have concluded that calving rates are strongly dependent on ocean temperatures. Until now, the role of the ocean (as opposed to the atmosphere) as the dominant driver of glacier frontal retreat on the western AP has not been considered…. We conclude that ocean temperatures below 100-m depth have been the predominant control on multidecadal glacier front behavior in the western AP.”
It should be pointed out that the decadal-scale changes in the heat content of the layers of abyssal vs. surface Southern Ocean are entirely consistent with what is expected with natural variability. As scientists Latif et al. (2013) explain:
“During phases of deep convection the surface Southern Ocean warms, the abyssal Southern Ocean cools, Antarctic sea ice extent retreats, and the low-level atmospheric circulation over the Southern Ocean weakens. After the halt of deep convection, the surface Southern Ocean cools, the abyssal Southern Ocean warms, Antarctic sea ice expands, and the low-level atmospheric circulation over the Southern Ocean intensifies, consistent with what has been observed during the recent decades.”
Referencing these natural heat changes and their climatic consequences, the ocean depth where there has been significant warming in the region of the AP in recent decades is primarily confined to the 150 to 400 m layer as identified by Cook et al. (2016). As the below graph from the paper shows, not only did the northern section of the 0-400 m layer not warm (as shown in the green/blue coloration areas), most of the 0-100 m layer for the AP region did not warm either. So the ocean warming for the AP has been primarily confined to the bottom half to three-quarters of the region, and only in the 150 to 400 m layer, not the 0-100 m layer, where it has been too cold to melt ice.
This lack of warming – and, in fact, cooling – in large sections of the oceanic and land-based Antarctic Peninsula region has been documented in other scientific studies. For example, Turner et al. (2016), in their paper entitled, “Absence of 21st century warming on Antarctic Peninsula consistent with natural variability,” have documented that the surface temperatures for the Antarctic Peninsula – which are often attributed to greenhouse gas forcing – have not warmed overall since the late 1970s, and in fact they’ve undergone a significant cooling trend for the last 1 1/2 decades.
“Here we use a stacked temperature record to show an absence of regional [Antarctic Peninsula] warming since the late 1990s. The annual mean temperature has decreased at a statistically significant rate, with the most rapid cooling during the Austral summer.”
Furthermore, Jones et al. (2016) have found that surfaces temperatures for the Southern Ocean – which surrounds the entire Antarctic continent – have dropped significantly since the late 1970s, as they show in the graph from their paper.
Of course, as the ocean surface near Antarctica has continued to cool for going on 4 decades now, this has led to a significant net growth in the overall sea ice area surrounding Anarctica, as also documented by Jones et al. (2016).
As further evidence that Antarctica as a whole has not been cooperating with climate models and the assumption that carbon dioxide is a significant determinant of glacier, sea ice, and temperature variability, Jones et al. (2016) conclude by saying that “climate model simulations that include anthropogenic forcing are not compatible with the observed trends” and that “natural variability overwhelms the forced response in the observations.”
“Over the 36-year satellite era, significant linear trends in annual mean sea-ice extent, surface temperature and sea-level pressure are superimposed on large interannual to decadal variability. Most observed trends, however, are not unusual when compared with Antarctic palaeoclimate records of the past two centuries.
“[C]limate model simulations that include anthropogenic forcing are not compatible with the observed trends. This suggests that natural variability overwhelms the forced response in the observations, but the models may not fully represent this natural variability or may overestimate the magnitude of the forced response.”
There are even graphs from the Jones et al. (2016) paper that show that West Antarctica, coastal East Antarctica, and the Antarctic Plateau have not undergone an obvious warming trend in the last 200+ years.
In fact, other recent studies also indicate that not only the AP, but the entire Antarctic continent’s temperatures have been stable to cooling slightly since the 1970s, and that, contrary to climate modeling, glaciers have been advancing more than they’ve been receding, or that ice melt volume has been declining (ice is melting less, not more) since the 1970s.
For example, like Cook et al. (2016) cited above, Kuippers Munneke et al. (2012) also conclude that atmospheric or surface warming (due to greenhouse gases, presumably) is not controlling glacier melt, but instead “a picture emerges in which the ultimate fate of ice shelves is governed by oceanic forcing from below“.
“None of the regions in Antarctica show a statistically significant trend in melt volume over the period 1979–2010. … Of the four Antarctic Peninsula stations that have an air temperature record for 1979–2010, only Faraday exhibits a statistically significant warming trend in summer temperature for that period. A reconstruction of [Antarctica] near-surface temperature….leaves DJF [December-February] temperature trends for 1979–2010 insignificant over nearly the entire continent, and mostly suggests statistically insignificant cooling along the coastal margins. This finding also seems consistent with RACMO2 DJF near surface temperatures, which show no statistically significant trends for 1979–2010 in any of the areas that experience melt. … A picture emerges in which the ultimate fate of ice shelves is governed by oceanic forcing from below.”
For East Antarctica, not only have surface temperatures been cooling since the early 1960s, a significant majority of glaciers have been advancing, not retreating, since about 1990.
“Here we present multidecadal trends in the terminus position of 175 ocean-terminating outlet glaciers along 5,400 kilometres of the margin of the East Antarctic ice sheet, and reveal widespread and synchronous changes. Despite large fluctuations between glaciers—linked to their size—three epochal patterns emerged: 63 per cent of glaciers retreated from 1974 to 1990, 72 per cent advanced from 1990 to 2000, and 58 per cent advanced from 2000 to 2010.”
Of course, none of these observed non-warming, glacier-advancing trends for Antarctica are compatible with assumptions about anthropogenic forcing, or the increase in CO2 emissions. In fact, scientists have even found that increasing CO2 concentrations has a net cooling effect, not a net warming effect, on central Antarctica.
“For this region [central Antarctica], the emission to space is higher than the surface emission; and the greenhouse effect of CO2 is around zero or even negative, which has not been discussed so far. We investigated this in detail and show that for central Antarctica an increase in CO2 concentration leads to an increased long-wave energy loss to space, which cools the Earth-atmosphere system. For most of the Antarctic Plateau, GHE-TES [greenhouse effect as measured by the Tropospheric Emission Spectrometer] is close to zero or even slightly negative; i.e., the presence of CO2 increases radiative cooling.”
So instead of an anthropogenic influence on trends in Antarctica, scientists are increasingly publishing papers documenting that the Antarctic climate is strongly dominated by natural factors (ENSO, SAM, planetary waves, etc.), not human activity. Even Eric Steig, avid defender of the CO2-dominated climate, recently acknowledged in a blog comment (#26) that “the evidence that the current retreat of Antarctic glaciers is owing to anthropogenic global warming is weak.”
Below are a tiny sample papers documenting a natural dominance over the Antarctic climate, and concluding that “detecting an anthropogenic signal … is challenging”. Unfortunately, these are the scientific papers that don’t get much attention, as they don’t endorse the humans-are-causing-dangerous-glacier-melting narrative that garners most of the headlines.
“[O]bservations indicate that there has been no significant change in Antarctic SMB [surface mass balance] in recent decades. We show that this apparent discrepancy between models and observations can be explained by the fact that the anthropogenic climate change signal during the second half of the twentieth century is small compared to the noise associated with natural climate variability. Using an ensemble of 35 global coupled climate models to separate signal and noise, we find that the forced SMB increase due to global warming in recent decades is unlikely to be detectable as a result of large natural SMB variability. However, our analysis reveals that the anthropogenic impact on Antarctic SMB is very likely to emerge from natural variability by the middle of the current century, thus mitigating future increases in global sea level.”
Predicting the Antarctic climate using climate models
“Climate models are the main tool for making quantitative estimates of how Antarctic climate may change over the 21st century. There is high agreement on some aspects of the predictions provided by models, but improvements in understanding are needed in key components of the Antarctic climate system, such as sea ice and coastal ocean-ice shelf processes. In the near term (on timescales of a few years) the climate change signal is small compared to natural cycles (associated with phenomena such as El Niño), the remote impacts of which on the Antarctic atmosphere are difficult to predict. In the longer term (on multi-decadal timescales) the reliability of climate model predictions is limited by uncertainty over human emissions pathways, the realism of climate models, and feedbacks between other elements of the Earth System (e.g. ice sheets).”
“Over the past 37 years, satellite records show an increase in Antarctic sea ice cover that is most pronounced in the period of sea ice growth. Detecting an anthropogenic signal in Antarctic sea ice is particularly challenging for a number of reasons: the expected response is small compared to the very high natural variability of the system; the observational record is relatively short; and the ability of global coupled climate models to faithfully represent the complex Antarctic climate system is in doubt.”
“ENSO is the most prominent coupled mode involving atmospheric and oceanic variability over the tropical Pacific and exerts strong impacts on the climate over the extra-tropics through the excitation of a large-scale atmospheric wave train. … The ENSO-induced atmospheric teleconnection, in turn, modulates Antarctic sea ice as well as sea surface temperature (SST) in the Southern Ocean through alteration of the surface energy fluxes. … SAM [southern annular mode] yields a clear local impact on the SH climate. For example, locally enhanced low-pressure anomaly to the west of the Antarctic Peninsula during a positive SAM [southern annular mode] phase results in advection of warm air and subsequent warming in the Antarctic Peninsula.”
“We demonstrate that a significant September trend towards increased convection (reduced OLR) in the poleward portion of the South Pacific Convergence Zone (SPCZ) is statistically related to Rossby wave-like circulation changes across the southern oceans. … OLR-related changes are linearly congruent with around half of the observed total changes in circulation during September and October, and are consistent with observed trends in South Pacific sea ice concentration and surface temperature over western West Antarctica and the western Antarctic Peninsula.”
“Large precipitation anomalies in regions of significant topography (e.g. New Zealand, Patagonia, coastal Antarctica) and anomalously warm temperatures over much of the Antarctic continent were also associated with strong planetary wave activity. The latter has potentially important implications for the interpretation of recent warming over West Antarctica and the Antarctic Peninsula.”
“Correct representation of the SSTs changes is important for the Northern Hemisphere, while correct representation of stratospheric ozone changes is important for the Southern Hemisphere. The ensemble-mean trend (which captures only the forced response) is nearly always much weaker than trends in reanalyses. This suggests that a large fraction of the recently observed changes [in sea surface temperatures, ozone] may, in fact, be a consequence of natural variability and not a response of the climate system to anthropogenic forcings.”