Antarctica Cooling Controversy - Observations of Trends

Observations of Trends

Antarctica has few long-term records. There are less than twenty permanent stations in all and only two in the interior. More recently AWSs supplement this, but their records are relatively brief. Hence calculation of a trend for the entire continent is difficult. Satellite observations only exist since 1981 and provide surface temperature measurements only in cloud-free conditions.

The 2007 IPCC Fourth Assessment Report states that Observational studies have presented evidence of pronounced warming over the Antarctic Peninsula, but little change over the rest of the continent during the last half of the 20th century. Chapman and Walsh note that "Trends calculated for the 1958–2002 period suggest modest warming over much of the 60°–90°S domain. All seasons show warming, with winter trends being the largest at +0.172 °C per decade while summer warming rates are only +0.045 °C per decade. The 45-yr temperature trend for the annual means is +0.082 °C per decade corresponding to a +0.371 °C temperature change over the 1958–2002 period of record. Trends computed using these analyses show considerable sensitivity to start and end dates, with trends calculated using start dates prior to 1965 showing overall warming, while those using start dates from 1966 to 1982 show net cooling over the region." Several scientific sources have reported that there is a cooling trend observed in the interior of the continent for the last two decades of the 20th century, while the Antarctic Peninsula shows a warming trend.

Doran et al. (2002) find that "Although previous reports suggest slight recent continental warming our spatial analysis of Antarctic meteorological data demonstrates a net cooling on the Antarctic continent between 1966 and 2000, particularly during summer and autumn. The McMurdo Dry Valleys have cooled by 0.7 °C per decade between 1986 and 2000, with similar pronounced seasonal trends... Continental Antarctic cooling, especially the seasonality of cooling, poses challenges to models of climate and ecosystem change".

In early 2013, David Bromwich, a professor of polar meteorology at Ohio State University, and a team including Antarctic weather station experts from the University of Wisconsin, published a paper in Nature Geoscience showing that the warming in central West Antarctica was unambiguous -- and likely about twice the magnitude estimated by Steig et al. The key to Bromwich et al.'s work was the correction for errors in the temperature sensors used in various incarnations of the Byrd Station record (the only long record in this part of Antarctica); miscalibraiton had previously caused the magnitude of the the 1990s warmth to be underestimated, and the magnitude of the 2000s to be overestimated. The revised Byrd Station record is in very good agreement with the borehole temperature data from nearby WAIS Divide.

There has been a public dispute regarding the apparent contradiction in the observed behavior of Antarctica, as opposed to the global rise in temperatures measured elsewhere in the world. This became part of the debate in the global warming controversy, particularly between advocacy groups of both sides in the public arena, including politicians, as well as the popular media. In contrast to the popular press, there is no evidence of a corresponding controversy in the scientific community.