Guest post by Mauri Pelto
It is popularly understood that glaciologists consider West Antarctica the biggest source of uncertainty in sea level projections. The base of the 3000-m thick West Antarctic Ice Sheet (WAIS) – unlike the much larger East Antarctic Ice Sheet – lies below sea level, and it has been recognized for a long time that this means it has the potential to change very rapidly. Most of the grounded West Antarctic ice sheet drains into the floating Ross and Ronne-Filchner ice shelves, but a significant fraction also drains into the much smaller Pine Island Glacier. Glaciologists are paying very close attention to Pine Island Glacier (”PIG” on map, right) and nearby Thwaites Glacier. In the following guest post, Mauri Pelto explains why.
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Guest Commentary by Andrew Monaghan and Marco Tedesco
Our study published in mid October in Geophysical Research Letters (Tedesco and Monaghan, 2009) documents record minimum snowmelt for Antarctica during austral summer 2008-2009 and lower-than-normal melt for several recent years, based on a 30-year satellite microwave record. Numerous blogs have cited the results as a challenge to previous studies reporting Antarctic warming, while also steadfastly ignoring other studies with similar results (e.g. Barrett et al., 2009). They have overlooked that these studies show that Antarctic warming has occurred mostly in winter and spring, whereas melting of course occurs in summer. And they oversimplify the causality and hence confuse our prediction for the future. We found that the same mechanism that has primarily caused low snowmelt in recent years will likely change in a manner that will enhance snowmelt in forthcoming decades. A brief summary follows. More »
I don’t tend to read other blogs much, despite contributing to RealClimate. And I’m especially uninterested in spending time reading blogs full of ad hominem attacks. But a handful of colleagues apparently do read this stuff, and have encouraged me to take a look at the latest commentaries on our Antarctic temperature story. Since I happen to be teaching about principal component analysis to my graduate students this week, I thought it would be worthwhile to put up a pedagogical post on the subject. (If you don’t know what principal component analysis (PCA) is, take a look at our earlier post, Dummy’s Guide to the Hockey Stick Controversy).
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Did you know that in 1965 the U.S. Department of Agriculture planted a particular variety of lilac in more than seventy locations around the U.S. Northeast, to detect the onset of spring — in turn to be used to determine the appropriate timing of corn planting and the like? The records the USDA have kept show that those same lilacs are blooming as much as two weeks earlier than they did in 1965. April has, in a very real sense, become May. This is one of the interesting facts that you’ll read about in Amy Seidl’s book, Early Spring, a hot-off-the-press essay about the impacts of climate change on the world immediately around us – the forest, the birds, the butterflies in our backyards.
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A couple of us (Eric and Mike) are co-authors on a paper coming out in Nature this week (Jan. 22, 09). We have already seen misleading interpretations of our results in the popular press and the blogosphere, and so we thought we would nip such speculation in the bud.
The paper shows that Antarctica has been warming for the last 50 years, and that it has been warming especially in West Antarctica (see the figure). The results are based on a statistical blending of satellite data and temperature data from weather stations. The results don’t depend on the statistics alone. They are backed up by independent data from automatic weather stations, as shown in our paper as well as in updated work by Bromwich, Monaghan and others (see their AGU abstract, here), whose earlier work in JGR was taken as contradicting ours. There is also a paper in press in Climate Dynamics (Goosse et al.) that uses a GCM with data assimilation (and without the satellite data we use) and gets the same result. Furthermore, speculation that our results somehow simply reflect changes in the near-surface inversion is ruled out by completely independent results showing that significant warming in West Antarctica extends well into the troposphere. And finally, our results have already been validated by borehole thermometery — a completely independent method — at at least one site in West Antarctica (Barrett et al. report the same rate of warming as we do, but going back to 1930 rather than 1957; see the paper in press in GRL).
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