Study Finds New Evidence of Warming in Antarctica

An illustration that depicts the warming that scientists have determined has occurred in West Antarctica during the last 50 years. The dark red shows the area that has warmed the most.

     Antarctica is warming.
     That is the conclusion of scientists analyzing half a century of temperatures on the continent, and the findings may help resolve a climate enigma at the bottom of the planet.
     Some regions of Antarctica, particularly the peninsula that stretches toward South America, have warmed rapidly in recent years, contributing to the disintegration of ice shelves and accelerating the sliding of glaciers. But weather stations in other locations, including the one at the South Pole, have recorded a cooling trend. That ran counter to the forecasts of computer climate models, and global warming skeptics have pointed to Antarctica in questioning the reliability of the models.
     In the new study, scientists took into account satellite measurements to interpolate temperatures in the vast areas between the sparse weather stations.
     "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," said Eric J. Steig, a professor of earth and space sciences at the University of Washington in Seattle, who is the lead author of a paper to be published Thursday in the journal Nature.
     Because the climate record is still short, more work needs to be done to determine how much of the warming results from natural climate swings and how much from the warming effects of carbon dioxide released by the burning of fossil fuels, Dr. Steig said.
     But Drew T. Shindell of the NASA Goddard Institute for Space Studies in New York, who is another author of the paper, said, "It's extremely difficult to think of any physical way that you could have increasing greenhouse gases not lead to warming at the Antarctic continent."
     Dr. Steig and Dr. Shindell presented the findings at a news conference on Wednesday. They found that from 1957 through 2006, temperatures across Antarctica rose an average of 0.2 degrees Fahrenheit per decade, comparable to the warming that has been measured globally.
     In West Antarctica, where the base of some large ice sheets lies below sea level, the warming was even more pronounced, at 0.3 degrees Fahrenheit, though temperatures in this area are still well below freezing and the warming will not have an immediate effect on sea level.
     In East Antarctica, where temperatures had been thought to be falling, the researchers found a slight warming over the 50-year period. With the uncertainties, East Antarctica may have indeed been cooling, but the rise in temperatures in the west more than offset the cooling. The average temperature for Antarctica is about minus 58 degrees.
     "There is very convincing evidence in this work of warming over West Antarctica," said Andrew Monaghan, a scientist at the National Center for Atmospheric Research in Boulder, Colo., who was not involved with the research.
     As with earlier studies, the scientists found that more recently, since the late 1970s, temperatures had actually cooled in East Antarctica, a phenomenon that many atmospheric scientists attribute to emissions of chlorofluorocarbons, a family of chemicals used as coolants that destroyed high-altitude ozone. Because those chemicals have since been phased out, the ozone hole is expected to heal, and the cooling trend may reverse.

     Il n'y a pas d'exception antarctique... L'ensemble du continent blanc se réchauffe bel et bien à l'instar du reste du globe, et non sa seule partie occidentale contrairement à ce que certains chercheurs pensaient.
     «On entend régulièrement répéter que l'Antarctique se refroidit, or ce n'est pas le cas», insiste Eric Steig, directeur du département Quaternaire à l'université de Washington à Seattle, co-auteur avec Drew Shindell, de l'Institut des Sciences spatiales de l'université Columbia, d'une étude publiée dans Nature.
     Au moment où la banquise Wilkins semble devoir se disloquer prochainement, ces chercheurs viennent verser une nouvelle pièce au dossier, regroupant des données fournies par les satellites ou recueillies sur le terrain depuis 1957. «Le réchauffement de la péninsule et de l'Antarctique occidental est lié aux changements de la circulation atmosphérique et à la diminution de la banquise dans le secteur Pacifique de l'océan austral», ont expliqué les chercheurs à l'occasion d'une conférence de presse par téléphone.

Un demi-degré en un demi-siècle
     «Une des raisons principales pour lesquelles on pensait que la plus grande partie de l'Antarctique Est refroidissait, c'est la présence du trou dans la couche d'ozone protectrice qui apparaît à partir du printemps dans la région polaire de l'hémisphère sud. Ce phénomène est responsable de la baisse des températures dans la partie orientale. Or, la situation dans cette zone Est a été extrapolée à la totalité du continent sans que rien ne vienne corroborer cette idée, souligne Eric Steig. Et si le trou dans la couche d'ozone disparaît au milieu de ce siècle, comme il est envisagé par les scientifiques, l'Antarctique dans son ensemble pourrait se réchauffer comme le reste du monde».
     Selon les multiples relevés pris en compte par les deux chercheurs, la température moyenne de l'ensemble de l'Antarctique a augmenté de 0,5°C depuis les années 1950, un ordre de grandeur très compatible avec l'ensemble du réchauffement climatique global.
     Les scientifiques concluent leur rapport dans Nature en affirmant que la hausse des températures dans l'Antarctique est difficile à expliquer sans faire intervenir l'augmentation des émissions gaz à effet de serre due aux activités de l'homme.

Topographie de l'Antarctique. Crédit: Institut polaire français