The new research, published in the journal Nature Geoscience, also provides the firmest proof to date that climate change at both poles is not the result of natural fluctuations.

"Our results demonstrate that human activities have already caused significant warming in both polar regions," said Alexey Karpechko, a professor at the University of East Anglia and a co-author of the study released yesterday.

Earlier investigations left no doubt that Earth's northern extremity has warmed at nearly twice the global average over the last century, causing a dramatic shrinking of sea ice and disrupting the region's ecosystems.

"However in Antarctica, such detection was so far precluded by insufficient data," said Karpechko.

The new study goes a long way toward filling that gap, and factoring out the causes.

Using new data on land surface temperatures and state-of-the-art computer models to simulate different climate scenarios, a team of scientists led by East Anglia's Nathan Gillet were able to tease apart the internal and external drivers of observed changes at both poles.

Rather than covering the entire Arctic and Antarctic regions, as previous studies have done, they focused only on the grid points where precise measurements have been taken.

This made their climate models more accurate, and showed that observed changes in temperatures over the 20th century could only have occurred if the impact of industrial greenhouse gas emissions, and upper atmosphere ozone depletion, are taken into account.