Surface temperatures in the Arctic since 2005 have been higher than for any five-year period since record keeping began in 1880, according to a new report from the Arctic Monitoring and Assessment Program, an international group within the Arctic Council that monitors the Arctic environment and provides advice on Arctic environmental protection.
The rate of sea-ice decline has accelerated and the decline rate in the past 10 years has been higher than the Intergovernmental Panel on Climate Change predicted in 2007, the report says.
"Evidence from lake sediments, tree rings and ice cores indicates that Arctic summer temperatures have been higher in the past few decades than at any time in the past 2000 years," the report says. "Previously unseen weather patterns and ocean currents have been observed, including higher inflows of warm water entering the Arctic Ocean from the Pacific."
Temperatures in the Arctic permafrost have risen by up to 3.5 degrees in the past two to three decades, and the southern limit of the permafrost has been moving north, with the limit having retreated by 80 miles in the past 50 years in the Canadian province of Quebec, for example, the report says.
Most Arctic glaciers and ice caps have shrunk in the past 100 years, especially in Canada and southern Alaska. Climate models predict a 10 to 30 percent drop in the mass of mountain glaciers and ice caps by the end of the century, with the melting of the Greenland ice sheet expected to accelerate.
Overall loss of snow and ice cover will likely heighten the warming trend, mainly because the white snow and ice tend to reflect heat from sun, rather than allowing the heat to be absorbed by the darker land or ocean water. Scientists now think that Arctic sea-ice cover will all but disappear in the summer by mid-century.
The absorption of more heat by the sea during the summer, as the ice cover retreats, has already caused an increase in air temperatures in the fall, while in the spring the snow has tended to melt progressively earlier, thus leading to a decrease in the number of winter days with on-land snow cover. On the other hand, the depth of the snow cover has varied between different regions. Climate models predict increases in overall precipitation and snow depths, although higher temperatures and early snow melts will likely lead to some drying out of Arctic land, the report says.
The warming of soils may increase the release of methane and carbon dioxide into the atmosphere, with these greenhouse gases potentially further accelerating the global warming.
The release of freshwater into the Arctic Ocean from melting ice could impact global ocean currents and climate systems, while the release of water from Arctic glaciers, ice caps and the Greenland ice cap could raise global sea levels from between 3 feet and 5 feet by 2100, the report says.
The loss of sea ice would cause a "devastating habitat loss" for some ice-adapted animals such as polar bears, Arctic seals and walruses, the report says. On land, the loss of permafrost and the changing snow cover will have varying impacts on the ecosystem, including benefits for some species, problems for others, and overall changes in plant and animal communities.
A reduction in coastline protection by ice is resulting in heightened coastal erosion, with coastal retreat rates of more than 6 feet per year being reported for sections of the coastlines of the Beaufort and Laptev Seas, the report says.
While the loss of Arctic sea ice could create new economic opportunities, including tourism and the opening of transpolar sea routes, the shrinking season of winter snow and ice cover on land will pose challenges for activities requiring the use of ice roads for transportation.
And rising sea levels increase the risk of flooding in low-lying coastal regions, with the potential for serious flooding in major coastal cities such as New York and Shanghai, the report says.
Communities need to adapt to the changes that are occurring as a result of the warming of the Arctic. As well as adaptation at a local level, national and international action is needed, to make any necessary changes to laws and regulations and to invest in any necessary infrastructure, such as new transportation networks.
And, in terms of mitigation, deep and immediate cuts are required in the emission of the greenhouse gases that most scientists blame for the high, observed rate of global warming, the report says. There also needs to be further research and environmental monitoring, to improve the various models for predicting the future climate and for predicting the impacts of climate change -- a number of the processes involved in climate change are poorly understood, and there is considerable uncertainty about the likely speed of change and the precise impacts of that change, the report says.