Record warmth in the Arctic in 2016 has caused massive declines in sea ice and snow and delayed the autumn freeze, scientists have warned.
The region saw record average air temperatures in the year from October 2015 to September 2016, according to the latest annual Arctic report card, backed by the US government's National Oceanic and Atmospheric Administration.
Record monthly highs were set in January, February, October and November, and the last two months have been 6C above the average for the last few decades - with temperatures 14C above normal recorded in some places.
The "unprecedented" warming air temperatures in the Arctic led to a record-breaking delay in the sea ice freezing up in the autumn, extensive melting of the Greenland ice sheet and record low spring snow cover in parts of the region.
Jeremy Mathis, director of Noaa's Arctic research programme, said: "Rarely have we seen the Arctic show a clearer, stronger or more pronounced signal of persistent warming and its cascading effects on the environment than this year."
Average temperatures over land in the Arctic have risen 3.5C since 1900, and continue to increase at double the rate of global temperature rises, according to the assessment which brings together the work of 61 scientists from 11 countries.
Spring snow cover was at a record low in the North American Arctic, with May's snow cover falling below 1.5 million square miles for the first time since satellite observations began in 1967.
The Greenland ice sheet continued to lose mass over 2016, with the start of melting coming close to the earliest recorded date, set in 2012.
As autumn arrived, the Arctic sea ice was at its lowest extent for the time of year from mid-October to late November. The sea ice is also thinning, the report found.
Arctic seas were 5C above the 1982-2010 average in some areas in August, while retreating ice and spring melt is boosting algae and other tiny marine plants which form the basis of the food chain.
But the Arctic Ocean is at risk of becoming more acidic as it absorbs more carbon dioxide, which could affect fisheries.
And the region's frozen tundra, which holds vast amounts of carbon and could have profound effects on the planet if it melts, is now releasing more carbon into the atmosphere than it is taking up.
Rod Downie, WW-UK polar programme manager, said: "The Arctic may seem like a long way away, but it's in our back yard. These changes are causing weather patterns to shift and sea levels to rise.
"The science cannot be clearer. The Arctic is dramatically changing as a result of our carbon emissions. This report card should be seen as yet another red flashing light.
"Protecting the future of the top of the world requires us to reduce emissions across the rest of the planet. The way forward now is to turn away from fossil fuels and embrace clean energy solutions."
