THE rapid warming of the Antarctic Peninsula during the second half of the 20th century has paused, according to a new study.

Researchers say stabilisation of the ozone hole along with natural climate variability were “significant” in bringing about the change.

They said that, together, these influences have now caused the peninsula to enter a temporary cooling phase.

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But temperatures remain higher than measured during the middle of the 20th century and glacial retreat is still taking place, reveal the findings by the British Antarctic Survey (BAS) published in the journal Nature.

Study lead author Professor John Turner said: “The Antarctic Peninsula climate system shows large natural variations, which can overwhelm the signals of human-induced global warming.

“In recent years, there has been an international research effort to explain what’s happening in the region and to understand the implications for the Antarctic environment and future sea-level rise.

“Our study highlights the complexity and difficulty of attributing effect to cause. The ozone hole, sea-ice and westerly winds have been significant in influencing regional climate change in recent years.

“Even in a generally warming world, over the next couple of decades temperatures in this region may go up or down, but our models predict that in the longer term, greenhouse gases will lead to an increase in temperatures by the end of the 21st century.”

The Antarctic Peninsula is the long mountainous strip of land that protrudes and extends towards South America. Its size is around three per cent of the continent.

Researchers from BAS said stabilisation of the ozone hole and changing wind patterns have driven a regional cooling phase that is temporarily masking the warming influence of greenhouse gases.

A wide range of climate data was analysed for the study, including atmospheric circulation fields, sea-ice records, ocean surface temperatures and meteorological observations from six Antarctic Peninsula research stations with near-continuous records extending back to the 1950s.

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During the Twentieth Century, Antarctic Peninsula temperatures increased by up to 0.5 C per decade, helping to trigger the dramatic collapse of ice shelves and causing many glaciers to retreat.

While there was a decrease in sea ice extent around the Antarctic Peninsula towards the end of the last century it has been increasing in recent years, particularly in the north-east of the region.

The cold easterly winds observed in the 21st Century have had a greater impact on the region because the sea ice has prevented ocean heat from entering the atmosphere.

To set their observations in a longer-term context, the researchers looked at a 2,000 year climate reconstruction using the chemical signals in ice cores.

Analysis suggests that peninsula warming over the whole 20th Century was unusual, but not unprecedented in the context of the past 2,000 years.

The reconstruction shows a warming starting in the 1920s, which is consistent with the warming trends recorded by the meteorological stations.

Dr Robert Mulvaney, a leading ice core researcher with BAS, said: “Meteorological observations from the Antarctic Peninsula research stations only cover the last 60 years or so.

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“If we are to get a better idea of the long-term trend we need to look back in time.

“The ice core record helps us see how the climate evolves over the longer term.”