Odds are humans cause record heat: scientists

Data shows 2015 as warmest year ever, which ‘can hardly be by chance’

The odds are “vanishingly small” that recent years of record warmth aren’t due to human emissions of greenhouse gases, researchers in the U.S. and Germany said, adding to pressure on world governments to cut back on fossil fuel use.

Data showing 2015 is the warmest year ever were published after their study was completed, and would make the odds even slimmer, PIK said in an emailed statement.

“2015 is again the warmest year on record, and this can hardly be by chance,” Stefan Rahmstorf, a co-author of the paper, said in the statement. “Natural climate variations just can’t explain the observed recent global heat records, but man-made global warming can.”

Scientists are increasingly attributing individual weather events to climate change, having previously been reluctant to do so, signalling only the trend of rising temperatures as evidence of human influence in the climate.

Envoys from 195 nations agreed in December in Paris to a new deal binding all countries for the first time to cut or limit greenhouse gases. That followed mounting evidence that runaway emissions threaten to make some parts of the world uninhabitable.

Researchers at the University of Oxford and the Royal Netherlands Meteorological Institute said earlier this month that global warming doubled the chances of December’s record U.K. rains occurring. The scientists in the latest study performed a statistical analysis combining observed data and computer simulations of the climate to calculate their odds.

“Natural climate variability causes temperatures to wax and wane over a period of several years, rather than varying erratically from one year to the next,” said Michael Mann, director of the Earth System Science Center at Penn State University.

“That makes it more challenging to accurately assess the chance likelihood of temperature records. Given the recent press interest, it just seemed like it was important to do this right, and address, in a defensible way, the interesting and worthwhile question of how unlikely it is that the recent run of record temperatures might have arisen by chance alone.”