Washington: Directly contradicting much of the Trump administration's position on climate change, 13 federal agencies have unveiled an exhaustive scientific report that says humans are the dominant cause of the global temperature rise that has occurred since the start of the 20th century, creating the warmest period in the history of civilisation.

Over the past 115 years, global average temperatures have increased 1.8 degrees Fahrenheit, leading to record-breaking weather events and temperature extremes, the report says.

The global, long-term warming trend is "unambiguous," it says, and there is "no convincing alternative explanation" that anything other than humans - the cars we drive, the power plants we operate, the forests we destroy - are to blame.

The report was approved for release by the White House, but the findings come as the Trump administration is defending its climate change policies on several fronts, with US President Donald Trump having declared the "war on coal" to be over.