The Arctic is undergoing rapid and possibly irreversible change, according to a new report prepared for the eight nations which rim the region.
Polar bears use the ice floes to hunt seals
The Arctic Climate Impact Assessment (ACIA) endorses recent warnings about melting ice, with perhaps all ocean ice disappearing in summers by 2060-2100.
The statement, to be published next week, has concerns too about raised levels of ultraviolet light brought about by ozone thinning.
It says the coming years will challenge the region's ecosystems and peoples.
The ACIA document recognises that average Arctic temperatures have risen at twice the rate seen elsewhere on the planet.
It records that permafrost is thawing, trees are moving north and some species, such as polar bears, are having to adapt their ways to survive the changing conditions.
The region is projected to warm an additional 4-7C by 2100.
The report does not list simply the negatives that will come from a warmer world. It also says agriculture may become easier in some areas, there should be improved access to oil and gas deposits and new shipping lanes will open up. Some fisheries could become more productive.
The ACIA document is the work of more than 300 scientists and has taken four years to compile and has undergone a rigorous peer-review process.
It is perhaps the most detailed study ever of how current warming trends are changing a single region of the Earth.
It was commissioned by the Arctic Council, the intergovernmental forum for countries with territories inside the region's 30 million square km: Canada, Denmark, Finland, Iceland, Norway, Russia, Sweden and the US.
It also includes six circumpolar indigenous peoples' organisations.
"The starting point for the assessment was the recognition that the Arctic was vulnerable in many different ways to climate change, and also that the Arctic played a fundamental role in regulating the Earth's climate," said Professor Terry Callaghan, an Arctic ecologist who helped produce the assessment.
"What happens there is not just an isolated factor of local interest. What happens there has important consequences for the rest of the world," the researcher attached to the universities of Sheffield (UK) and Lund (Sweden) told BBC News.
"There're vast stores of carbon in permafrost and in ocean sediments and if they get warmer, they could significantly impact the rest of the world."
The report reviews current knowledge and considers "environmental, human health, social, cultural and economic impacts and consequences, including policy recommendations."
Arctic sea ice has shrunk both in thickness and in extent. Data collected by submarines shows there was about a 40% reduction in draught between the 1960s and 1990s - by draught, researchers mean the ice that lies between the surface of the ocean and the bottom of the ice pack.
The melt seems to have slowed somewhat in recent years and may slow further if a natural climate phenomenon known as the Arctic Oscillation switches its current phase and prevents the drift of warmer waters into the region.
Even so, says Professor Peter Wadhams, an expert on Arctic sea ice, the trend will still be towards an ice-free Arctic Ocean in summer months.
"The models give a spread of dates from about the 2060s and 2070s to 2100," the polar ocean physicist from Cambridge University, UK, told BBC News.
"There's quite a big range of uncertainty but it should occur some time in the second half of the century."
He added: "In modelling, they're quite conservative; they put in big error bars because they are concerned that there may be some new physics that we don't know about."
Ice reflects sunlight back into space. As it disappears, the Earth will absorb more of the Sun's energy, so increasing the rate of warming.
But more directly, the ACIA says, "the reduction in sea ice is very likely to have devastating consequences for polar bears, walruses, ice-living seals, and local people for whom these animals are a primary food source".
A warmer future will radically alter the ranges of the Arctic's plants and animals, such as the reindeer/caribou. Currently, about 600 million birds are thought to breed annually in the region. Some of their favourite tundra nesting sites will be restricted.
The Arctic's infrastructure will also have to be re-thought in some instances. The foundations of some buildings will destabilise and vital winter roads will become impassable as the permafrost melts.
Another issue of significant interest is the increase in UV light now reaching the surface because industrial chemicals have conspired with the polar atmosphere to thin the ozone layer.
Although an international treaty has now banned the most harmful chemical culprits, computer models expect ozone repair to take several decades.
As a consequence, the ACIA says, the current generation of Arctic young people is likely to receive a lifetime dose of ultraviolet radiation that is about 30% higher than any prior generation. This could have deleterious health effects, such as more skin cancers and immune system disorders.
Campaign groups are concerned the warnings in the report will be ignored by the Arctic Council nations. The US, for example, has recently restated its opposition to the Kyoto process to restrict emissions of carbon dioxide (CO2), the main human-produced gas thought by many scientists to be warming the planet at an unnatural rate.
"The big melt has begun," said Nicola Saltman, climate change programme leader at WWF.
"Life on Earth will change beyond recognition with the loss of the ice sheet at the North Pole and higher sea levels threatening major global cities such as London and other coastal communities.
"This report shows that climate change is happening now and highlights the urgent need for immediate action, starting with the Arctic governments, who must reduce their CO2 emissions."