Wednesday, May 11, 2016

Antarctic Temperatures

There is no doubt that Antarctica is not warming as fast as the rest of the globe. It's not entirely clear whether it is warming at all. The small or nonexistent warming in Antarctica is consistent with most global warming models. Some parts of the continent are clearly warming, while others are not, or not warming as much. Wikipedia has a good summary of the state of scientific opinion:

Changes in the average temperature of the Antarctic continent has been the subject of various measurements. The trend differs at different locations on the continent.[3] These trends have been labelled as "contradictory" in some accounts.[4][5][6] Observations unambiguously show the Antarctic Peninsula to be warming. Some trends elsewhere on the continent have shown cooling,[7][8][9] while others show show warming over the entire continent,[10] but overall trends are smaller and dependent on season and the timespan over which the trend is computed. Climate models predict that temperature trends due to global warming will be much smaller in Antarctica than in the Arctic,[11] mainly because heat uptake by the Southern Ocean acts to moderate the radiative forcing by greenhouse gases.

The apparent contradiction in the observed cooling behavior of Antarctica between 1966 to 2000 became part of the public debate in the global warming controversy, particularly between advocacy groups of both sides in the public arena, as well as the popular media. In his novel State of Fear, Michael Crichton asserted that the Antarctic data contradict global warming.[12] The few scientists who have commented on the supposed controversy state that there is no contradiction,[13] while the author of the paper whose work inspired Crichton's remarks has said that Crichton "misused" his results.[14] There is no similar controversy within the scientific community, as the small observed changes in Antarctica are consistent with the small changes predicted by climate models, and because the overall trend since comprehensive observations began is now known to be one of warming. At the South Pole, where some of the strongest cooling trends were observed between the 1950s and 1990s, the mean trend is flat from 1957 through 2013.

In a study released in 2009, historical weather station data was combined with satellite measurements to deduce past temperatures over large regions of the continent, and these temperatures indicate an overall warming trend. One of the paper's authors, Eric J. Steig of the University of Washington, stated "We now see warming is taking place on all seven of the earth’s continents in accord with what models predict as a response to greenhouse gases."[15] A follow-up study by O'Donnell and others that strongly criticized the Steig et al. work nevertheless found significant warming in West Antarctica. O'Donnell et al. also confirmed that Antarctica overall has been warming since the 1950s, but disagreed with Steig et al. about the strength of that warming. Subsequent measurements of temperatures in a borehole at the center of the West Antarctic ice sheet, by Orsi and others,[16] found even larger positive trends than Steig et al.

I would add that some authors have seen a long period North-South oscillation which might currently be amplifying NH warming and diminishing SH warming.