More “consensus” science: Antarctica not influenced by AGW
By Kenneth Richard
In recent years, the headlines of common news sources have austerely warned that West Antarctica is melting rapidly:
- “‘Nothing can stop retreat’ of West Antarctic glaciers” — BBC
- “The melting of Antarctica was already really bad. It just got worse.” — Washington Post
- “West Antarctic glacier loss: We have passed the point of no return“ — Christian Science Monitor
- “Antarctic ice melting so fast the whole continent may be at risk“ — The Guardian
Then, last November (2015) a NASA study (Zwally et al., 2015*) was released indicating that the growth in the Antarctic ice sheet (AIS) has been exceeding the losses since the early 1990s, and that the net mass gains from the AIS were negatively contributing to sea level. This, of course, did not affirm the alarmist headlines.
RealClimate, an AGW blog co-founded by Gavin Schmidt and Michael Mann, necessarily cobbled together a response to the inconvenient study. After all, a growing polar ice sheet in response to anthropogenic global warming did not advance the cause.
The result was an essay written by Jonathon Bamber – “So what is really happening in Antarctica?”** – which essentially characterized the Zwally et al. (2015) conclusion as a peculiar outlier. Most other papers on Antarctic ice sheet mass balance indicate that the AIS is losing about -50 to -100 Gt/year on average (which is the equivalent of about one inch per century of sea level rise contribution).
These studies were characterized as more likely to be accurate than the NASA-sponsored paper that found a net AIS gain of about +100 Gt/year. In other words, “consensus” logic (the more people agree, the more likely they are to be right) was employed to “refute” the NASA study. This graph (below) from the RealClimate essay was featured as a visual representation of just how “out-there” the Zwally et al. (2015) paper was compared to the “consensus” conclusions of other scientists:
Sometimes, though, a thorough reading of entries on AGW blogs like RealClimate can prove enlightening. Buried in the comment section of this same essay — comment number 26 to be specific — was an admittance by Dr. Eric Steig (moderator of comments) that the evidence that the Antarctic ice sheet (AIS) responds to anthropogenic global warming, is “weak.” Not only that, he acknowledged that about half of scientists agree with him on this.
Dr. Eric Steig’s Comment 26:
I think the evidence that the current retreat of Antarctic glaciers is owing to anthropogenic global warming is weak. The literature is mixed on this, about 50% of experts agree with me on this.”
The admission that Antarctica may not respond to CO2 emissions, or anthropogenic global warming (AGW) in general, has been affirmed several more times in other recent scientific analyses. The most recent example is a peer-reviewed paper by Smith and Polvani (2016) published online just last week. These scientists set out to determine if anthropogenic forcing can explain why West Antarctica has warmed substantially in the last few decades, or why East Antarctica has not warmed substantially during the same period.
After analyzing the factors involved for the warming of West Antarctica and the peninsula, Smith and Polvani concluded that an anthropogenic signal is “completely absent” when “natural climate variability” is included. In other words, “natural climate variability” is the driving force behind the West Antarctica and peninsula warming, and “there is little evidence of anthropogenic SAM-induced driving of the recent temperature trends.”
Below are the key points from the paper Smith and Polvani, 2016:
The recent annually averaged warming of the Antarctic Peninsula, and of West Antarctica, stands in stark contrast to very small trends over East Antarctica. This asymmetry arises primarily from a highly significant warming of West Antarctica in austral spring and a cooling of East Antarctica in austral autumn. Here we examine whether this East–West asymmetry is a response to anthropogenic climate forcings or a manifestation of natural climate variability. We compare the observed Antarctic surface air temperature trends over two distinct time periods (1960–2005 and 1979–2005), and with those simulated by 40 models participating in Phase 5 of the Coupled Model Intercomparison Project (CMIP5). We find that the observed East–West asymmetry differs substantially between the two periods and, furthermore, that it is completely absent from the forced response seen in the CMIP5 multi-model mean, from which all natural variability is eliminated by the averaging. We also examine the relationship between the Southern Annular mode (SAM) and Antarctic temperature trends, in both models and reanalyses, and again conclude that there is little evidence of anthropogenic SAM-induced driving of the recent temperature trends. These results offer new, compelling evidence pointing to natural climate variability as a key contributor to the recent warming of West Antarctica and of the Peninsula.
Here is a further sampling of some (6) other recently-published papers indicating that an anthropogenic forcing (warming) signal may not be detectable for Antarctica, or that natural variability dominates in that region:
Our analysis suggests that internal climate variability played a more significant role than external forcings in short-term SAT variability in the regions of the North Atlantic, the North Pacific, the Arctic, the Antarctic Peninsula, and its surrounding oceans.
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.
Introduction: It is expected that the observed recent atmospheric warming in this region [Bellingshausen-Amundsen coast region between the Antarctic Peninsula and West Antarctica] will result in increased snow accumulation, although the stable water isotopes from Ellsworth Land ice cores have shown that the recent rise in temperature here is not unusual in the past 300 years [Thomas et al., 2013]. Therefore, it is unclear whether these recent glaciological changes are part of a longer term natural trend or associated with anthropogenic climate forcing.
For East Antarctica, no general warming and increase in precipitation is found in surface observational data (Turner et al., 2005; Monaghan et al., 2006, 2008). This is important because an increase in precipitation, and hence increased surface mass balance (SMB), might mitigate sea level rise. … We conclude that, in the last 2 centuries, conditions in the interior DML [Dronning Maud Land, East Antarctica] have been fairly stable and only weakly influenced by changes in atmospheric dynamics.”
The Amundsen Sea low (ASL) is a climatological low pressure center that exerts considerable influence on the climate of West Antarctica. Its potential to explain important recent changes in Antarctic climate, for example, in temperature and sea ice extent, means that it has become the focus of an increasing number of studies. … The ASL has deepened in recent decades, affecting the climate through its influence on the regional meridional wind field, which controls the advection of moisture and heat into the continent. Deepening of the ASL in spring is consistent with observed West Antarctic warming and greater sea ice extent in the Ross Sea.”
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.
Yet, let’s assume the alarmist headlines are actually true and that indeed Antarctica has been melting rapidly, or has eclipsed the “point of no return.” If the burgeoning scientific “consensus” is that Antarctica is likely not responding to anthropogenic or CO2 forcing, or that warming trends (for West Antartica and the peninsula) are predominantly a consequence of natural variability, the alarmist headlines forecasting an Antarctic ice melt catastrophe effectively lose their impact.
Apparently the scientifically “weak” evidence that the Antarctic climate is significantly affected by anthropogenic forcing doesn’t make a good headline.