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Natural causes ‘extremely unlikely’ to be behind record global temperatures

Lake Hume, Australia. (Tim J Keegan/flickr)

We did it! Together, humanity changed the world (cue fireworks and the band.)

Together we set a new record in 2015 – the hottest year in recorded history. And a new study gives us the credit for this streak of global warming. The odds that we can give ‘natural causes’ the credit are extremely low.

Go ahead, pat yourself on the back.

“We find that individual record years and the observed runs of record-setting temperatures were extremely unlikely to have occurred in the absence of human-caused climate change, though not nearly as unlikely as press reports have suggested,” said Michael Mann and his co-authors in a study for the journal Scientific Reports.

The certainty that humans caused the record temperatures is not quite as high as some media reports make it out to be, but it is still likely our fault. Last week the National Oceanic and Atmospheric Administration officially announced that 2015 was the hottest year since 1880, when global temperatures were first recorded. The global average temperature was 1.62 F warmer than the 20th century average. Just land temperatures beat out the averages by even more.

The El Niño weather pattern shares some of the credit for the margin of the record. Scientists said earlier in 2015 that the record was likely to be broken because of its arrival and peak toward the end of the year. By beating the record set the previous year, the concern is that global warming overall is on the rise and it cannot be attributed solely to a cyclical global weather event.

hottest year updateThe 21st century is only 15 years old, yet global temperature records have been set in 13 of those years. It is hard to imagine that such a string of records is natural. The new study shows that the odds that human-made climate change is not behind the warming temperatures for the Northern Hemisphere to be between 1 in 5,000 and 1 in 170,000 – better odds than winning Powerball, but still slim.

Some media reports stated that the odds of the recent run of record temperatures to be 1 in 650 million. The research shows that the real odds of it being a natural occurrence to be much better, but it is still small enough for the researchers to arrive at the same conclusion – it is almost certainly our fault.

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

And while there is a new global temperature record, it may be wise to save a few fireworks for next year. Another new report shows that 2016 may be even warmer than 2015, thanks also to El Niño. It will also likely mark the official end to the overall slow down of global warming experienced over the past decade.


About Author

Tom Murphy

Tom Murphy is a New Hampshire-based reporter for Humanosphere. Before joining Humanosphere, Tom founded and edited the aid blog A View From the Cave. His work has appeared in Foreign Policy, the Huffington Post, the Guardian, GlobalPost and Christian Science Monitor. He tweets at @viewfromthecave. Contact him at tmurphy[at]