* Ozone hole causes Antarctic sea ice to grow
* Study helps resolve global warming puzzle
By Alister Doyle, Environment Correspondent
OSLO, April 21 (Reuters) - An expansion of sea ice around Antarctica is linked to a hole in the ozone layer high in the atmosphere, according to a study on Tuesday that helps clear up a mystery about global warming.
The findings, by scientists at the British Antarctic Survey (BAS) and the U.S. space agency NASA, explain an apparent contradiction between a thaw of ice in the Arctic to record lows and an increase in ice around Antarctica over the past 30 years.
"This new research helps us solve some of the puzzle of why sea ice is shrinking in some areas and growing in others," John Turner of BAS, the lead author of the report, said.
The scientists said damage by manmade chemicals to the ozone layer, which shields the planet from ultra-violet rays that can cause skin cancer, cooled the stratosphere and disrupted wind patterns around Antarctica.
The shift meant winds blew off the continent more often, cooling the sea and creating more ice, they said. Scientists found a hole in the ozone layer over Antarctica in the 1980s and traced it to chemicals once used in refrigerants or hairsprays.
"While there is increasing evidence that the loss of sea ice in the Arctic has occurred due to human activity, in the Antarctic human influence through the ozone hole has had the reverse effect and resulted in more ice," Turner said.
Sea ice around Antarctica has expanded at a rate of around 100,000 sq kms (38,610 sq miles) a decade since the 1970s and covers an area of about 19 million sq kms at its winter maximum, doubling the size of the continent.
By contrast, summer sea ice around the North Pole shrank in 2007 to the smallest since satellite records began in the 1970s. The U.N. Climate Panel says warming is caused by greenhouse gases from burning fossil fuels that will bring more floods, heatwaves, droughts and rising sea levels.
"Although the ozone hole is in many ways holding back the effects of greenhouse gas increases on the Antarctic, this will not last, as we expect ozone levels to recover by the end of the 21st century," Turner said in a statement.
Tom Lachlan-Cope, a BAS meteorologist and one of the co-authors of the study in the journal Geophysical Research Letters, said Antarctica's sea ice had expanded most in the Ross Sea, south of New Zealand.
"It's the classic way that sea ice is produced. You get an offshore wind which blows the ice away from the shore and exposes open sea water which then freezes over because of the cold air," he told Reuters.
Understanding Antarctica is a priority for scientists since it locks up enough ice to raise sea levels by 57 metres (190 ft) if it were ever to melt. Even a tiny thaw could threaten low-lying Pacific islands, or cities from New York to Beijing.
-- For Reuters latest environment blogs click on: blogs.reuters.com/environment/ (Editing by Farah Master)