Recent Antarctic Warming Attribution Complicated By ENSO Events?

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It should easy to attribute the warming to ENSO events. It’s already been done.

The recently released paper by Steig et al (2009) “Warming of the Antarctic ice-sheet surface since the 1957 International Geophysical Year” generated a lot of buzz on the climate blogs today.
http://www.nature.com/nature/journal/v457/n7228/full/nature07669.html

Making the rounds, the paper was discussed at (In the order I found them):

Watts Up With That
http://wattsupwiththat.com/2009/01/21/antarctica-warming-an-evolution-of-viewpoint/

Climate Audit
http://www.climateaudit.org/?p=4914

Nature.com Climate Feedback
http://blogs.nature.com/climatefeedback/

Accuweather
http://global-warming.accuweather.com/2009/01/antarctica_as_a_whole_is_indee.html#comments

Jennifer Marohasy
http://jennifermarohasy.com/blog/2009/01/modellers-remove-evidence-of-cooling-and-editor-removes-comment-by-climate-sceptic/

Climate Research News
http://climateresearchnews.com/2009/01/hockey-team-plays-in-antarctica/

(Of course, I left comments at some, and many of those comments dealt with the same topics. They follow.)

But I found the post at RealClimate my Michael Mann and Eric Steig, co-authors of the study, the most enlightening.
http://www.realclimate.org/index.php/archives/2009/01/state-of-antarctica-red-or-blue/

In it they wrote, “3) Our paper — by itself — does not address whether Antarctica's recent warming is part of a longer term trend. There is separate evidence from ice cores that Antarctica has been warming for most of the 20th century, but this is complicated by the strong influence of El Niño events in West Antarctica. In our own published work to date (Schneider and Steig, PNAS) we find that the 1940s [edit for clarity: the 1935-1945 decade] were the warmest decade of the 20th century in West Antarctica, due to an exceptionally large warming of the tropical Pacific at that time.”

The title of the linked Schneider and Steig, PNAS paper is “Ice cores record significant 1940s Antarctic warmth related to tropical climate variability.”
http://www.pnas.org/content/105/34/12154.abstract

Abstract:
“Although the 20th Century warming of global climate is well known, climate change in the high-latitude Southern Hemisphere (SH), especially in the first half of the century, remains poorly documented. We present a composite of water stable isotope data from high-resolution ice cores from the West Antarctic Ice Sheet. This record, representative of West Antarctic surface temperature, shows extreme positive anomalies in the 1936–45 decade that are significant in the context of the background 20th Century warming trend. We interpret these anomalies—previously undocumented in the high-latitude SH—as indicative of strong teleconnections in part driven by the major 1939–42 El Niño. These anomalies are coherent with tropical sea-surface temperature, mean SH air temperature, and North Pacific sea-level pressure, underscoring the sensitivity of West Antarctica's climate, and potentially its ice sheet, to large-scale changes in the global climate.”

It would seem logical to conclude that the current bout of warming in the Western Antarctic could be attributable to the recent almost three-decade-long bout of ENSO activity that has been dominated by El Nino events.

The following are the comments with graphs that I posted at Watts Up With That. Notice a theme?

The following are graphs of Antarctic and Southern Ocean TLT [AHU MSU] created from data available through the KNMI Climate Explorer Website. Keep in mind that the MSU satellite data does not reach the entire Antarctic. In fact, RSS only lists data as far South as 70S. AHU extrapolates, smoothes, estimates, whatever, to provide data for the rest of the Antarctic. Regardless, here are additional graphs of the AHU TLT data for the Antarctic to add to the ones I put up yesterday for those discussing the Antarctic off-topic on the previous thread.
Here are the East and West TLT anomalies from 90S to 60S with linear trends. The trend in the west is flat, and the trend in the east toward cooling:

http://i39.tinypic.com/9hqeeh.jpg

The Southern Ocean would influence that dataset so I reduced the longitudes in the following to 90S to 70S. Again, this is apparently estimated data that’s outside the reach of the MSU satellite as far as I know. Finally, a dataset with a warming trend: http://i42.tinypic.com/b69i6e.jpg

You’d have to segment the data looking for an area that’s warming differently that the rest of the continent in order to come up with one that’s even more significant.

There’s a phenomenon that effects Antarctic sea ice called the Antarctic sea ice dipole, which has ENSO as one of its primary influences, so I decided to take a look at the Antarctic TLT dipole, which I calculated as Western TLT MINUS Eastern TLT for 90S to 70S and compared it to scaled NINO3.4 SST anomalies. There’s some very apparent ENSO influence and at times it’s hard to tell what drives what. Curious. http://i41.tinypic.com/2lunv5.jpg
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Here are the graphs I posted as part of the off-topic comments on yesterday’s thread.
Has the Antarctic warmed? Yes. Has it warmed in recent years? No. Unless you use surface temperature data, then you have a rise in recent years.

Lower troposphere temperature: http://i39.tinypic.com/2d0i2hu.jpg

A blurb from my post on Surface Temperature By Continent. Scroll down for the Antarctic:
http://bobtisdale.blogspot.com/2009/01/land-surface-temperature-comparison-by_07.html

It included a comparative graph of GISS, CRUTEM, and NCDC data for the Antarctic: http://i39.tinypic.com/33nkxfc.jpg

And the capper that seems to contradict their claim that the recent Antarctic cooling is a result of the change in ozone, blah, blah. How did man vary ozone in the early period of this graph to cause that drop in SST anomalies from 1880 to 1920? The peak in the 1980s/90s didn’t come close to reaching the SSTs at the end of the 19th century. http://i44.tinypic.com/2uen29u.jpg

One of the authors of the Nature paper, Eric Steig, made an appearance at Lucia’s website and had a discussion with Roger Pielke Jr that’s worth reading. I, of course, had to throw a few graphs into the conversation.
http://rankexploits.com/musings/2008/who-expects-a-tropical-tropospheric-hot-spot-from-any-and-all-sources-of-warming/#comments

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And for those interested in the TLT of the Antarctic Peninsula, here’s a graph of it compared to scaled NINO3.4 SST anomalies and to Sato Index data. The anomalous dip in 1986 appears to be the cause of the positive trend in Antarctic Peninsula Lower Troposphere Temperature. http://i41.tinypic.com/rt43ns.jpg
I should be posting the rest of the Antarctic data in a day or two at my website.
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In looking at the CRUTEM, GISS, and NCDC Surface Temperature data (January 1950 to Dec 2008) for the West Antarctic (available through the KNMI Climate Explorer website)... http://i40.tinypic.com/vp7pdt.jpg
...there are a number of things that stand out:
1. The NCDC and CRUTEM anomalies have increased since 1969 (period referenced in the study), while GISS remained relatively flat. The study wouldn’t deal with this, just an observation.
2. There appears to be a difference in the number of sampled surface stations between NCDC and the other two from the 1960s to the early 80s. Also not related to the study.
3. But, related to the study, during periods of volcanic activity (excluding El Chichon), year-to-year variability appears to decrease.
4. And the NCDC and CRUTEM data appear to have step changes that could be linked to the 1982/83 and 1997/98 El Nino events.
Did the paper discuss these, especially the ENSO-induced step changes?

If you’ve never heard of ENSO-induced step changes, there are discussions of it here in a two-part series:
http://bobtisdale.blogspot.com/2009/01/can-el-nino-events-explain-all-of.html
http://bobtisdale.blogspot.com/2009/01/can-el-nino-events-explain-all-of_11.html
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CLOSING COMMENT

I’ll repeat my above conclusion:
It would seem logical to conclude that the current bout of warming in the Western Antarctic could be attributable to the recent almost three-decade-long bout of ENSO activity that has been dominated by El Nino events.