More research was needed, UNEP said, into the possibility of a runaway release of methane trapped in frozen soils in Siberia, Canada, Alaska and Nordic countries.
"The unknowns about the amount and rate of methane release from the thawing Arctic makes it a wild card when considering climate change risks," Reuters reported UNEP head Achim Steiner as saying.
Arctic methane emissions were projected to at least double during the 21st century, the report said, partly because of an increase in wetlands caused by thawing of permafrost.
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