The heat is on in West Antarctica

Regular followers of RealClimate will be aware of our publication in 2009 in Nature, showing that West Antarctica — the part of the Antarctic ice sheet that is currently contributing the most to sea level rise, and which has the potential to become unstable and contribute a lot more (3 meters!) to sea level rise in the future — has been warming up for the last 50 years or so.

Our paper was met with a lot of skepticism, and not just from the usual suspects. A lot of our fellow scientists, it seems, had trouble getting over their long-held view (based only on absence of evidence) that the only place in Antarctica that was warming up was the Antarctica Peninsula. To be fair, our analysis was based on interpolation, using statistics to fill in data where it was absent, so we really hadn’t proven anything; we’d only done an analysis that pointed (strongly!) in a particular direction.

It has been a strange couple of years in limbo: we have known with certainty for at least two years that our results were basically correct, because there was a great deal of very solid corroborating evidence, including the borehole temperature data that confirmed our basic findings, and data from automatic weather stations near the center of West Antarctica that we hadn’t used, but which Andy Monaghan at Ohio State (now NCAR) had shown also corroborated our results. But most of this work was unpublished until very recently, so it wasn’t really usable information.

So it was a nice early Christmas present to see the publication of a new assessment by the well-known guru of Antarctic meteorology, David Bromwich, along with his students and colleagues at Ohio State, the University of Wisconsin (who run the U.S. automatic weather station program in Antarctica) and NCAR, which back up our results. Actually, they do more than back-up our results: they show that our estimates were too conservative and that West Antarctica is actually warming by about a factor of two more than we estimated. They also agree with the key interpretation of the results that both we and David Schneider and colleagues at NCAR have presented: that in the winter and spring seasons, when the most rapid warming is occurring in West Antarctica, the driver has been changes in the tropical Pacific, not the ozone hole (which is invoked too frequently, in my view, to explain everything from penguin populations to sea ice changes).

The borehole temperature data were published earlier this year by Orsi et al. in Geophysical Research Letters. The new temperature reconstruction of Monaghan was included as part of a paper (Küttel et al.) on ice core records in Climate Dynamics, also earlier this year; it was also included in the reconstruction in Schneider et al. 2011 in Climate Dynamics. Both showed unambiguously that West Antarctic is warming up, as fast as the Antarctic Peninsula. Bromwich et al. gets this same result again.

If it sounds like I don’t think Bromwich et al.’s results are anything new, let me correct that impression. The contribution of this new paper is huge. Bromwich et al. rely almost entirely on local data to produce the best-possible record of temperature from one location — Byrd Station in central West Antarctica. In contrast, our work relied heavily on interpolation of data from weather stations some distance from West Antarctica. Why didn’t we use the same data Bromwich et al. did? Well, we did, but the problem is that the Byrd Station record is actually several different records, taken at different times using different instruments. We felt that we could not splice these records together into one continous record, because instrument inter-calibration issues could easiily create spurious trends.

One of the chief contributions of the Bromwich team is that they carefully checked the calibration on the various temperature sensors and dataloggers that are used in the Byrd automatic weather station. It turns out that there were significant calibration issues and that correcting for them makes the temperature higher in the 1990s but somewhat lower in the 2000s (though still higher than in the 1960 – 1980s). That is a compelling finding, because it puts the weather station data in better agreement with the climate forecast reanalysis data explaining the cause of the winter warming trends (as described e.g. in Ding et al., 2011; 2012).

Another new aspect of the Bromwich et al. paper is that it shows that there is significant warming even in summer time in West Antarctica. This could arguably bode ill for the West Antarctic Ice Sheet, since if current trends continue it will mean more melting on the ice shelves there — ultimately leading to their collapse, as has already happened on the Antarctic Peninsula.

As Anais Orsi and I discuss in a News & Views article — not yet online, but evidently to be in the Februrary print issue of Nature Geoscience[Update, Steig and Orsi is now online here]– Bromwich et al.’s results are objectively the best record available of the last five decades of temperature change in West Antarctica. Note that the while the borehole data are the most important independent validation, they provide only a smoothed look at past temperatures; they do not resolve interannual or decadal variability. Bromwich et al.’s updated record for Byrd Station should now be routinely incorporated into global temperature compilations such as those done by GISS and CRU. Doing so will, I think, change the picture of climate change in the Southern Hemisphere, and not insignificantly.

There’s a lot more to be said — including some reasons why I don’t think the likelihood of surface-snow-melt-driven collapse of ice shelves is very high in West Antarctica — but I’m off to enjoy a respite from the internet for a few days. I’m going somewhere nice and cold and snowy.

That Youtube video you posted is an excellent example of
good communication about the known (and unknown) facts
about Climate Science (as well as the politics) imho.
THX I have already shared it with others.

>”Bromwich et al.’s updated record for Byrd Station should now be routinely incorporated into global temperature compilations such as those done by GISS and CRU. Doing so will, I think, change the picture of climate change in the Southern Hemisphere, and not insignificantly.”

[Response: Well, as I explained here, they would have gotten a better answer had those chosen any other parameter for a particular part of their routine than they did. I pointed this out in my review, but those chose to ignore it. I make no comment as to why.

I also noted that O’Donnell et al. treated the occupied Byrd station and Byrd AWS stations as two independent data sets, and because their calculations (like ours) remove the mean of each record, O’Donnell et al. removed information that might be rather important: namely, that the average temperatures in the AWS record (post 1980) are warmer — by about 1°C — than the pre-1980 manned weather station record. This observation, of course, is the precisely the basis of Bromwich et al.’s work. I considered this myself, but didn’t trust the instrument calibration at the time. I was right, as it turns out (as Bromwich et al. discovered, and for which they corrected). –eric]

Both the Antarctic peninsula and the WAIS have apparently undergone marked warming during the last 50 years. However the WAIS and Antarctic annual temperatures show negligible correlation.

That seems somewhat anti-intuitive to me. In my mind the correlation coefficient would be determined by plotting each annual temperature of WAIS against each corresponding annual temperature of the peninsula. Presumably they were both relatively lowish 50 years ago and relatively warmish now and somewhat intermediate at intermediate years.

So is the absence of correlation due to the large standard deviations in the temperature data? Or is the correlation determined in some other way? Or do annual temperatures tend to go up in the peninsula when they tend to go down on the WAIS? or what…?

[Response: The Peninsula is anti-correlated with West Antarctica on interannual timescales, because shifts in the trajectory of storms will tend to favor one area or another. But on the long timescale they are warming up together. This is probably because while the position of storms varies year to year, the average number of storms that bring warm air into the area has increased everywhere. The area of the Peninsula that is most highly correlated with the updated Byrd record is Faraday station, which is usually the station cited as showing the rapid warming on the Peninsula.–eric]

On the local level, variability is still much larger than the warming trend. Here are more complete maps of temperature correlation to Byrd. There are still huge areas of negative correlation. It’s not very different on the northern hemisphere, where the trend is up almost everywhere. The maps show mostly weather; patterns that persist over several months are more likely to be climate. Data are from NCEP reanalysis 2, including the reference values near Byrd where the trend is about .1 K/a in R2.

[Response: Nicely done. Though notably, there are no negative correlations with Byrd anywhere in West Antarctica. To the extent these correlations apply to the longer timescale then it is warming everywhere in West Antarctica (as of course we showed back in 2009).–eric]

ABSTRACT
Cenozoic temperature, sea level and CO2 co-variations provide insights into climate sensitivity to external forcings and sea level sensitivity to climate change. Pleistocene climate oscillations imply a fast-feedback climate sensitivity 3 ± 1°C for 4 W/m2 CO2 forcing for the average of climate states between the Holocene and Last Glacial Maximum (LGM), the error estimate being large and partly subjective because of continuing uncertainty about LGM global surface climate. Slow feedbacks, especially change of ice sheet size and atmospheric CO2, amplify total Earth system sensitivity. Ice sheet response time is poorly defined, but we suggest that hysteresis and slow response in current ice sheet models are exaggerated. We use a global model, simplified to essential processes, to investigate state-dependence of climate sensitivity, finding a strong increase in sensitivity when global temperature reaches early Cenozoic and higher levels, as increased water vapor eliminates the tropopause. It follows that burning all fossil fuels would create a different planet, one on which humans would find it difficult to survive.

A very nice comparison of recent work, but I note that, just as the global temps have been in a stillstand for nearly a decade, so it is with the West Antarctica–no significant rise since 2,000 or so.
Comments?

[Response: not really. I think we have discussed many times why short term linear trends are not predictive of anything very much – and that goes double for single points. – gavin]

“… with the color coding according to the phase of ENSO, the eye is able to compare apples to apples: the upward long-term trend during El Niño years (red triangles) is plain, the upward long-term trend during neutral years (green squares) is plain, and the upward long-term trend during La Niña years (blue diamonds) is plain.

Stare hard enough, though, and you see that they have leveled off. The last ten data points have little or no trend. But we see that the lack of trend is at least partly due to the El Niño year near the beginning of the 10-year period and the two La Niña years near the end.

Let’s get quantitative about this. In this case, with the temperature rise being nearly linear, it helps to add trendlines….”

Eric, yes, that blog post discussion begins by citing “A recent paper I like by Foster and Rahmsdorf … takes a statistical approach to attempt to eliminate the effect of the other known forcing mechanisms, and what’s left over is a fairly steady warming….. I decided to take a simple approach at looking at the effect of ENSO….”

Then he goes on using three charts — the attribution “as least partly” from looking at the first of the three — then he goes further:

He says “Let’s get quantitative” and does the analysis, shown in two more charts, to bring the reader to the conclusion:

“… All else being equal, an El Niño year will average about 0.2 C warmer globally than a La Niña year. Each new La Niña year will be about as warm as an El Niño year 13 years prior….”

Eric Steig wrote:
“the average number of storms that bring warm air into the area has increased everywhere”

Polar amplification is a testable prediction rooted in the basic physics of AGW theory, and is particularly important because it can be validated or refuted in the reasonably near term. Storminess increases can of course also be related to AGW, but how can the effect of the increase in storms be teased from the true physics-based polar amplification of warming in Antarctica in order to independently evaluate the prediction of polar amplification?

[Response: Testing the changes storms against “prediction” will be difficult, if not impossible. As for polar amplification, which aspect of the basic physics are you referring to? The most obvious one is that polar amplification is predicted from the Stefan Boltzmann equation (you have to warm up cold places more, in order to balance the same radiative forcing). But there is also the sea-ice albedo effect, which is completely separate. And on real planets like earth, dynamical changes play a huge rule. In Antarctica, the wind field — not thermodynamics — dominates the sea ice response. “Basic physics” doesn’t always lead to quiite-so-simple testable predictions (though, not incidentally, climate models generally have little polar amplification over the Southern Ocean and Antarctica because ocean heat uptake increases most in the Southern Ocean as the climate warms). See our post on polar amplification from a few years back (here) for more discsussion. — eric]

[Response: It is warming nearly everywhere but at a statistically insignificant rate. South Pole can no longer be said to be cooling — the trend over the entire record (1957-2011) is flat. You can get the data here if you are interested.–eric]

Saw this paper on the day of return from AA peninsula. Can anyone explain why the AA sea ice extent was apparently so great this year? They also report a great deal of snow fall, which I understand. Thanks.

“According to … recent study Claire Parkinson and Donald Cavalieri of NASA’s Goddard Space Flight Center, Antarctic sea ice increased by roughly 17,100 square kilometers per year from 1979 to 2010. Much of the increase, they note, occurred in the Ross Sea, with smaller increases in Weddell Sea and Indian Ocean. At the same time, the Bellinghausen and Amundsen Seas have lost ice. “The strong pattern of decreasing ice coverage in the Bellingshausen/Amundsen Seas region and increasing ice coverage in the Ross Sea region is suggestive of changes in atmospheric circulation”

That last link says in part

“… Since 1980 …. loss of ozone caused atmospheric pressure to decrease over the Amundsen Sea, thereby strengthening the winds on the Ross Ice Shelf, according to NASA Goddard scientist Josefino Comiso, coauthor of a recent study that models the connection between ozone, wind speeds, and climate in the Antarctic. The changes help explain one of the paradoxes of the Antarctic: while sea ice in some areas is growing rapidly, it’s retreating at a rapid pace in others.

The new model suggests that colder, stormier, and faster winds are rushing over the waters encircling Antarctic — especially the Ross Sea, where ice growth has been the most rapid. The winds create areas of open water near the coast – known as polynyas – that promote sea ice production.

At the same time, warmer air from higher pressure systems are simultaneously encroaching upon the Antarctic Peninsula, one sliver of the continent that is experiencing rapid warming….”

[Response: That’s an okay paper, the idea that atmospheric circulation is driving sea ice changes is not new. And that paper ignores all the evidence (!!) for what’s happening in West Antarctica. Much more relevant are the paper from two years ago by Schneider and others (here), and this year by Holland et al. (Wind driven trends in Antarctic sea-ice drift). You can read about the latter paper in the Guardian, here. Of course, the best answer to the question about the Peninsula this year is that there is a lot of stochastic interannual variability in the winds, and it can’t always be pinned down to one thing (e.g. an El Niño year).–eric]