OSLO, Norway (Reuters) — A record-breaking string of hot years since 2000 is almost certainly a sign of man-made global warming, says a new study.
It said there is a vanishingly small chance that the heat streak was caused by random, natural swings.
Last year was the hottest since records began in the 19th century. It’s part of a trend that almost all scientists blame on greenhouse gases caused by the burning of fossil fuels, 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 ex-perts wrote in the journal Scientific Reports.
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The study, which was written before 2015 temperature data was released, estimated that the chance of the record run being random with no human influence was one in 770 to one in 10,000. Up to 13 of the 15 warmest years were from 2000-014.
Lead author Michael Mann, a professor of meteorology at Pennsylvania State University, said the group’s computer simulations indicated that the odds had widened to one in 1,250 to one in 13,000 once 2015 was included.
“Climate change is real, human-caused and no longer subtle. We’re seeing it play out before our eyes,” he said.
Natural variations include shifts in the sun’s output and volcanic eruptions, which dim sunlight.
“Natural climate variations just can’t explain the observed recent global heat records, but man-made global warming can,” said Stefan Rahmstorf, a co-author from the Potsdam Institute of Climate Impact.
The scientists tried to account for factors including that heat from one warm year spills into the next. As well, temperatures in many years are almost identical, making it hard to rank their heat with confidence.
The United Nations’ World Meteorological Organization recently confirmed U.S. and British data showing 2015 was by far the hottest year on record and noted that a powerful El Nino 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.
