Record hot years almost certainly caused by man-made warming, study finds

Is it possible that the recent global records broken for 'hottest year' are caused by natural climate variation? In theory, but the chance is no better than 1 in 770 and may be as slim as 1 in 10,000, a new study suggests.

WMO confirms 2015 was hottest year on record as study shows hot years since 2000 likely not random

Human-caused climate change has been linked to problems such as heat waves, droughts and wildfires. This forest fire in Ventura County, California December 26, 2015, burned over 400 hectares of land. (Gene Blevins)

A record-breaking string of hot years since 2000 is almost certainly a sign of man-made global warming, with vanishingly small chances that it was caused by random, natural swings, a study showed on Monday.

Last year was the hottest since records began in the 19th century in a trend that almost all scientists blame on 
greenhouse gases from burning of fossil fuels, which have been stoking heat waves, droughts, downpours and rising sea levels.

"Recent observed runs of record temperatures are extremely unlikely to have occurred in the absence of human-caused global warming," a U.S.-led team of experts wrote in the journal Scientific Reports.

Written before 2015 temperature data were released, it estimated the chance of the record run — with up to 13 of the 15 warmest years all from 2000 to 2014 — was between one in 770 and one in 10,000 if the series were random with no human influence.

Lead author Michael Mann, a professor of meteorology at Pennsylvania State University, told Reuters that the group's 
computer simulations indicated those odds including 2015 had widened to between one in 1,250 and one in 13,000.

The sun is seen behind smoke billowing from a chimney of a heating plant in Taiyuan, Shanxi province December 9, 2013. Last year was the hottest since records began in the 19th century in a trend that almost all scientists blame on greenhouse gases from burning of fossil fuels. (Reuters)

Climate change is real, human-caused and no longer subtle — we're seeing it play out before our eyes," he wrote in an 
e-mail. Natural variations include shifts in the sun's output or volcanic eruptions, which dim sunlight.

"Natural climate variations just can't explain the observed recent global heat records, but man-made global warming can," Stefan Rahmstorf, a co-author from the Potsdam Institute of Climate Impact, said in a statement.

The scientists tried to account for factors including that heat from one warm year spills over into the next. And 
temperatures in many years are almost identical, making it hard to rank their heat with confidence.

Last month, almost 190 nations agreed at a summit in Paris to the strongest deal yet to shift from fossil fuels towards 
cleaner energies
such as wind and solar power to limit warming. 

Natural causes of climate variation include shifts in the sun's output or volcanic eruptions, such as this eruption of Italy's Mount Etna in December 2015, which dim sunlight. But they're unlikely to be enough to explain recent global heat records, scientists say. (Antonio Parrinello/Reuters)

Separately on Monday, the U.N.'s World Meteorological Organization (WMO) confirmed U.S. and British data showing 2015 was by far the hottest year on record and noted that a powerful El Nino event, warming the surface of the Pacific Ocean, had stoked extra heat.

"The power of El Nino will fade in the coming months but the impacts of human-induced climate change will be with us for many decades," WMO Secretary-General Petteri Taalas said.