Martin Mejia/AP/File
A group of tourists walk past a photo featuring an image of the Pastoruri glacier, during a tour called 'The Route of Climate Change' in Huaraz, Peru, on Aug. 12, 2016. The melting of glaciers such as Pastoruri has put cities such as Huaraz, located downslope from the glacier about 35 miles away (55 kilometers), at risk from what scientists call a 'glof,' a glacial lake outburst flood.

When did global warming begin? Maybe earlier than we thought

Researchers say man-made climate change caused by greenhouse gas emissions can be tracked as far back as the mid-1800s, rather than the late 1800s, as previously thought. 

When did manmade global warming begin? A new study suggests it could have been decades earlier than we had thought. 

Until now, scientists believed that climate change started in the late 1800s. But using coral, microscopic organisms, ice cores, cave samples, tree rings and computer simulations, researchers were able to track very slight changes in temperature in North America, Europe and Asia going back as far as 1850. 

The study, published Wednesday in the journal Nature, suggests that Earth may have warmed about a third of a degree Fahrenheit, or 0.2 degrees Celsius, between 1850 and 1880. Industrial greenhouse gas emissions were the cause of the warming, just as they are now, though the change was significantly slower back then: In the past 30 years, the planet has warmed about nine-tenths of a degree. 

The findings tell us that "the speed at which the climate responds to even a small change in greenhouse gases appears to be quite fast," said study lead author Nerilie Abram, a paleoclimate scientist at the Australian National University, to the Associated Press. 

Ed Reading, a climate researcher at the University of Reading in Englad who was not involved with the study, told The Washington Post that the research is "further evidence that the climate has already changed significantly since the pre-industrial period." 

But not all scientists agree with the findings. Michael Mann, a Pennsylvania State University climate scientist who is credited with the "hockey stick" concept – the theory that there were only minor variations in temperature from 1000 A.D. until the start of the 20th century, when there was a dramatic upswing – argues that any warming prior to the late 19th century was simply the Earth's natural reaction to a cooling effect produced by volcanic eruptions in 1815.

"There was certainly some anthropogenic warming prior to the late 19th century," Dr. Mann said in an email to the Post, citing some of his recent research to support his argument. "But the authors overstate how much, and how early, by incorrectly conflating early 1800s warming caused by the recovery from these eruptions with early greenhouse warming." 

John Fasullo, a climate scientist at the National Center for Atmospheric Research, told the Associated Press that he agreed with Mann. 

The researchers said they also initially attributed the early change to this volcanic cooling effect, but computer simulations suggested otherwise. 

Determining when and why global warming began not only helps us understand the past, Dr. Abrams told the AP, it could also help us better understand the future. If the team's findings are correct and man-made greenhouse gas emissions were responsible for the Earth heating up in the mid-1800s, it could point either to a worse future climate than previously predicted if greenhouse gases aren't controlled, or a faster recovery if efforts to reduce emissions are successful.  

This report contains material from the Associated Press. 

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