US report contradicts Trump, affirms global warming

A report by the US Government has affirmed that global warming is real and "extremely likely" caused by human activities, a stark contrast with President Donald Trump's position on climate change.

The 477-page report, part of a congressionally mandated review conducted every four years known as the "National Climate Assessment", showed that global annually averaged surface air temperature has increased by about 1.0 degree Celsius over the last 115 years.

"This period is now the warmest in the history of modern civilization," media reports quoted the assessment, officially titled the "Climate Science Special Report", as saying.

"The last few years have also seen record-breaking, climate-related weather extremes, and the last three years have been the warmest years on record for the globe," it said.

"These trends are expected to continue over climate timescales."

Based on extensive evidence, the report concluded that it is "extremely likely" — meaning a 95 to 100 per cent probability — that human activities, especially emissions of greenhouse gases, are the dominant cause of the observed warming since the mid-20th century.

"For the warming over the last century, there is no convincing alternative explanation supported by the extent of the observational evidence."

The report also warned that the magnitude of climate change beyond the next few decades will depend primarily on the amount of greenhouse gases, especially carbon dioxide, emitted globally.

Trump once called climate change a "hoax" and his administration considered efforts to fight global warming just to "be a waste of your money", a position met with widespread criticism both at home and abroad.