Arctic ice may be melting faster than most, climate change science has concluded, the conservation group WWF said in a report.
It found that ice in Greenland and across the Arctic region was retreating "at rates significantly faster than predicted in previous expert assessments".
The Greenland Ice Sheet - with an ice volume of about 2.9 million cubic kilometres - is shrinking at a fast pace and "could contribute much more than previously estimated to global sea-level rise during the 21st century," the WWF said.
It also said that Arctic warming has reduced both the area and thickness of the northern region's multi-year sea ice, making it more prone to summer thaw.
Many climate change scientists have inadequately considered the drivers of such trends, such as interactions between sea ice thickness and water temperature, according to WWF.
"The recent acceleration in sea-ice retreat is not captured by most models," it said in the study reviewing global warming research from 2005, including the UN Intergovernmental Panel on Climate Change (IPCC) reports issued last year.
"Our understanding of climate impacts lags behind the changes we are already seeing in the Arctic," said Martin Sommerkorn, a climate change advisor with WWF International's Arctic Programme.
"This is extremely dangerous, as some of these Arctic changes have the potential to substantially warm the Earth beyond what models currently forecast," he said.
WWF, formerly called the World Wildlife Fund and now known by its initials, said that climate change has already affected all aspects of ecology in the Arctic, including the region's oceans, sea ice, ice sheets, snow and permafrost.
It called on Arctic nations - including Canada, the US, Russia, Iceland, Norway, Sweden, Finland, and Denmark, through its Greenland territory - to work together to help the region's communities adapt to the challenges ahead.
Fast-melting Arctic ice has the potential to cause coastal erosion, impact indigenous peoples' livelihoods, affect marine organisms, and make the region's mineral and other resources more accessible with new, formerly inaccessible marine routes.
It could also have global effects, particularly causing rising sea levels that could threaten coastal communities from Bangladesh to the Netherlands to parts of the US.
"We need to reduce global emissions of greenhouse gases to levels that will avoid the continued warming of the Arctic and the anticipated resulting disruption of the global climate system," Mr Sommerkorn said.