Warming at the top of the world is happening twice as fast as the rest of the globe, and extending unnatural heating into the northern autumn and winter, according to a new US federal report.

In its annual Arctic Report Card , the National Oceanic and Atmospheric Administration today tallied record after record of high temperatures, low sea ice, shrinking ice sheets and glaciers.

Study lead author Jeremy Mathis, NOAA's Arctic research chief, said it shows long-term Arctic warming trends deepening and becoming more obvious, with a disturbing creep into seasons beyond summer, when the Arctic usually rebuilds snow and ice.

Scientists have long said man-made climate change would hit the Arctic fastest.
Mathis and others said the data is showing that is what's now happening.

"Personally, I would have to say that this last year has been the most extreme year for the Arctic that I have ever seen," said Mark Serreze, director of the National Snow and Ice Data Centre in Boulder, Colorado, who wasn't part of the 106-page report. "It's crazy."

NOAA's peer-reviewed report said air temperatures over the Arctic from October 2015 to September 2016 were "by far the highest in the observational record beginning in 1900." The average Arctic air temperature at that time was 2C warmer than the 1981-2010 average.

It's 3.5C warmer than 1900.