The Arctic has been warmer for the past five years than at any other point since 1900 when records began, according to a US government agency report.

Dramatic changes are being felt across the polar region as global warming triggers knock-on effects from earlier plankton blooms to more extreme weather.

The Arctic experienced its second warmest air temperatures and second lowest sea-ice coverage in 2018.

Polar temperatures are rising at roughly double the rate of the global average, and according to scientists behind the latest analysis this is causing "unexpected" changes in the environment.

Shifting patterns in the global jet stream linked to this warming have coincided with unusual conditions further south, including the freezing "Beast from the East" that struck Britain.

These events are outlined in the National Oceanic and Atmospheric Administration’s (NOAA) latest annual Arctic Report card.

It is the latest warning from US scientists about the enormous threat posed by climate change, even as president Donald Trump continues to voice his scepticism about its existence.

“The Arctic is experiencing the most unprecedented transition in human history,” said Dr Emily Osborne, who led the report.

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“These changes are impacting Arctic residents and have the potential to affect people well beyond the region.”

Dr Osborne noted that in the 13 years the NOAA has been publishing these reports, the warming trend has continued to increase in severity.

Additional threats to the Arctic come from ocean plastic contamination, which is on the rise, and human expansion into the region.

Nations including the US and Russia have expressed an interest in expanding their fossil fuel drilling in the Arctic, and melting ice is opening previously inaccessible shipping lanes further north.

“The environmental changes in the Arctic underscore why NOAA continues to invest in Arctic research and activities, which improve the nation’s economic competitiveness, national security, and the sustainable management of natural resources,” said retired Navy Rear Admiral Timothy Gallaudet, acting under-secretary of commerce for oceans and atmosphere at NOAA.

“This report will also help guide NOAA’s priorities in better understanding the role of the Arctic in climate change and extreme weather; sustaining and growing fisheries; and supporting adaptation and economic opportunities in the region.”

The findings have been released weeks after a US government report concluded that climate change resulting from excessive fossil fuel use was a major threat to both American lives and the nation’s economy.

Responding to the report, the unashamedly pro-fossil fuel president told reporters that he simply did not believe it.

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However, Mr Gallaudet refused to be drawn on the subject of the US administration’s climate scepticism.

“The White House has been a firm supporter of our research in the Arctic, not just NOAA but nationally,” he said, noting that the Arctic research was considered “important for national security”.

Mr Trump's administration has been rolling back Obama-era environmental regulations in an effort to maximise fossil fuel production, and has announced the withdrawal of the US from the Paris climate agreement.