"All the evidence points toward human-made effects playing a major role in the changes that we see at both poles and evidence that contradicts this is very hard to find," said Jennifer Francis, an atmospheric scientist at Rutgers University in New Jersey.

An examination of many previous studies about polar climate, to be published May 6 in the journal Eos, "further depletes the arsenal of those who insist that human-caused climate change is nothing to worry about," Francis said in a telephone briefing.

In the Arctic, Francis and co-authors of the research said, warming spurred by human-generated carbon dioxide emissions has combined with natural climate variations to create a "perfect Arctic storm" that caused a dramatic disappearance of sea ice last year, a trend likely to continue.

'NEW STATE'

"Natural climate variability and global warming were actually working together and they've sent the Arctic into a new state for the climate that has much less sea ice," said James Overland, an oceanographer at the US National Oceanic and Atmospheric Administration. "There's very little chance for the climate to return to the conditions of 20 years ago."

In Antarctica, the ozone hole adds a new factor to an already complicated set of weather patterns, according to Gareth Marshall of the British Antarctic Survey.

The changes in air pressure that go along with depleted stratospheric ozone are responsible for an increase in the westerly winds that whip around the Southern Ocean, at latitudes a bit north of most of Antarctica.

These winds isolate much of the southern continent from some of the impact of global warming, Marshall said. The exception is the Antarctic Peninsula, which reaches northward toward South America. There, the effects of warming have been dramatic, he said, because the winds that protect the rest of Antarctica do not insulate the peninsula.

The stratospheric ozone hole, caused by the ozone-depleting release of chemicals found in refrigerants and hair sprays, is likely to fully recover by 2070 as less of these chemicals are in use, as a result of international agreements.

The ozone layer shields Earth from harmful solar radiation, but its recovery is likely to open the way for warming in central Antarctica, the scientists said.