European scientists say thawing Arctic shorelines could trigger a release of methane gas that would be devastating to the world's climate and economy. They are calling the situation an "invisible time bomb."
The scientists' report, in the journal Nature, says the cost to the world economy would be $60 trillion.
Billions of tons of methane has been trapped under the Arctic ice for thousands of years. But the scientists say it could leak out amid warming global temperatures due in part to the greenhouse gas effect.
Their report says methane gas is about 20 times more effective in trapping the sun's heat than carbon dioxide. The scientists say a massive release of methane from the Arctic could trigger coastal floods, drought, severe storms, and extreme heat.