January 3, 2012

Antarctic Temperature Trends

Filed under: Antarctic, Climate Changes, Polar

Almost exactly two three years ago, a prominent paper became a media darling as it, according to the alarmist website Real Climate “appeared to reverse the ‘Antarctic cooling’ meme that has been a staple of disinformation efforts for a while now.”

The Nature paper, by Eric Steig and colleagues, made the cover on the January 22, 2009 issue.


Figure 1. Cover of January 22, 2009 issue of Nature magazine (left) showing the map of temperature trends across Antarctica as determined by the analysis of Steig et al. (right).

Despite Real Climate’s predictable take on the situation, many long-time students of Antarctic climate change (including usn’s here at WCR) yawned. It has been known for decades that there is a net warming in Antarctic surface temperature that began during the International Geophysical Year in 1957. However, what is also well known, is that the vast majority of the observed warming in Antarctica took place from the late 1950s through the early 1970s and that since then—during a period going on 40 years now—there has been very little net temperature change over Antarctica taken as a whole.

What the Steig et al. analysis did do, was to alter the generally accepted spatial pattern of the temperature change across Antarctica. Whereas previous studies showed that the warming was largely limited to the Antarctic peninsula region of West Antarctica with vast areas of cooling occurring distributed across the other parts of the continent, the Steig et al. analysis effectively spread the warming across the entire continent, both during the complete period of record since 1957, as well as during the most recent two-to-three decades (Figure 2).


Figure 2. Spatial patterns of temperature change across Antarctica as determined by Steig et al. for different time periods (adapted from O’Donnell et al., 2011).

Almost immediately, speculation popped up across the blogosphere that something was seriously amiss with Steig’s methodology. Analysts zeroed in on the problems and went on to publish in the scientific literature their own version of the spatial patterns of temperature change across Antarctica using the same data as Steig et al. used (a combination of surface observations and satellite-borne measurements) but employing a new and improved technology.

Surprise, surprise. The “new” map of temperature change across Antarctica produced by O’Donnell et al. wasn’t all that much different from the pre-Steig vision of the temperature changes which had taken place. Once again, the warming was primarily constrained to the Antarctica Peninsula, and cooling could be found across large regions of the rest of Antarctica (Figure 3).


Figure 3. Spatial patterns of temperature change across Antarctica as determined by a methodology used by O’Donnell et al. for different time periods (adapted from O’Donnell et al., 2011).

The situation presented in Figure 3 is much different from that presented in Figure 2.

For those who still question whether or not the O’Donnell et al. methodology is superior to the Steig et al. methodology, there is an independent arbiter—the satellite-derived temperature of the lower atmosphere that has been compiled and maintained by Roy Spencer and John Christy, and which just celebrated its 33rd birthday on December 1, 2011. The Spencer and Christy temperature record employs a different sort of satellite-borne temperature instrument (a microwave sounder unit, or MSU) than the satellite data melded with the surface observations in the Steig et al. and O’Donnell et al. studies, and is as a completely independent temperature data source.

Figure 4 shows the south polar projection of the trends in the lower atmosphere as derived from Spencer and Christy’s MSU data from December 1978 through November 2011. Compare Figure 4 with the lower two panels of Figures 2 and 3.


Figure 4. Spatial patterns of temperature change across Antarctica as determined by the MSU satellite data, December 1979-November 2011 (figure provided by John Christy).

Notice that there is a lot of blue shading on this map indicating regions where the temperature trend is negative (cooling), and that the regions of warming are primarily located along the continental margins.

The Spencer and Christy trends from the lower atmosphere are a decent (although imperfect) match with the O’Donnell et al. temperature trends of the surface. The Steig et al. trend analysis as the odd-one-out.

In the two years since the big flash at Nature, further and better analysis confirms that what has been going on in Antarctica is pretty much what we knew to be happening all along—that during the last 3-to-4 decade period of rapid build-up of atmospheric carbon dioxide, the temperature has changed little at the continental scale, and instead is characterized by a complex pattern of regional warming and cooling. Such changes do not foreshadow a rapid loss of continental Antarctic ice nor an alarming Antarctic contribution to the rate of current and future sea level rise this century as a result of surface ice melt. In fact, measurements from a different satellite data set that begin in 1979 show that the extent of ice in the southern high latitudes is increasingly significantly.

References:

O’Donnell, R., et al., 2011. Improved methods for PCA-based reconstructions: case study using the Steig et al. (2009) Antarctic temperature reconstruction. Journal of Climate, 24, 2099-2115.

Steig, E. J., et al., 2009. Warming of the Antarctic ice-sheet surface since the 1957 International Geophysical Year. Nature, 457, 459–462.




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