In recent decades, rapid warming of the western edge of the Antarctic Peninsula has seen plants moving in to colonize the area and Adélie penguins moving out. Although alarming, scientists thought that the warming — which has been disproportionate to that seen in most parts of the world — was a localized phenomenon, and that the bulk of the continent's interior was actually cooling. But a team led by Eric Steig of the University of Washington in Seattle, has shown that Antarctic warming extends beyond the peninsula and covers most of West Antarctica.

Earlier studies of Antarctic warming were based largely on discontinuous, ground-level observations from sparsely distributed weather stations. These included little data from West Antarctica, from which the penisula — a mountainous, icy arm of land that swirls in a northerly direction towards South America — extends. Steig's team has reconstructed Antarctic surface-temperature trends from 1957 to 2006 using satellite data and air-temperature records from weather stations.

Since the late the 1990s, Steig has been part of the International Trans Antarctic Scientific Expedition, an effort aiming to study hundreds of years of past climate and environmental change. As part of this project, Steig and researchers from other universities collected ice cores in West Antarctica, an area of relatively rapid snow accumulation, ideal for ice-core research. “But there was virtually no weather-station data there with which to compare the ice core records,” he says. “I needed to extract more information than was available in the literature to make sense of the ice-core records.”

In 1999, Steig realized he could use the surface-temperature measurements gathered by satellites. But at that point these had collected only 18 years' worth of data, so he faced a wait of almost a decade before he would have enough to produce meaningful results. In 2001, David Schneider, then a PhD student in Steig's lab, began to dig into the satellite data that was available and analyse it more thoroughly. Satellites do not make direct measurements of surface temperatures, instead calculating them from measurements of the radiation emitted from snow, so the data come with uncertainties. “David's work showed us the limitations of the satellite data, but also that it was more reliable than most people had assumed,” says Steig.

By 2007, Steig finally had the 25 years' worth of data he needed, and teamed up with Michael Mann at Pennsylvania State University, University Park. They applied an algorithm that allowed them to fill in missing data across the Antarctic continent as far back as 1957, revealing the warming in West Antarctica. Careful examination of climate modelling results suggested that this warming relates to the regional loss of sea ice over at least the past 25 years (see page 459). Their results were initially met with scepticism. “Everyone I talked to said 'There's no way that's right.'” says Steig. But, with detailed explanations, he managed to change opinions. “Some then realized that they had data that supported us pretty strongly,” he says.

Now Steig is heading back out into the field as a member of a team aiming to drill an ice core to the bottom of the West Antarctic ice sheet. Other researchers will take temperature measurements in the borehole, providing a definitive test of Steig's results — the cooler temperatures of the 1950s should still be detectable at depth.