Doyle Rice ,
Published April 24, 2017
Record-breaking weather events, especially heat waves but also downpours and droughts, can be linked to man-made global warming, a new study says.
“Our results suggest that the world isn’t quite at the point where every record hot event has a detectable human fingerprint, but we are getting close,” said study lead author Noah Diffenbaugh, a climate scientist at Stanford University.
It’s the first research to look specifically at the link between record weather events of the past several decades and climate change. Diffenbaugh and his team found that in over 80% of the heat records — which included both record hot days and months — there was a clear-cut signal of global warming.
Man-made climate change, aka global warming, is caused by the burning of fossil fuels such as gas, coal and oil, which release greenhouse gases such as carbon dioxide (CO2) into the atmosphere. This extra CO2 causes temperatures of the atmosphere and oceans to rise, allows the atmosphere to hold more water vapor (which can add extra fuel to storms), and causes global sea levels to rise.
Diffenbaugh also found that record-breaking extremes of precipitation can be tied into global warming, but the signal wasn’t as strong: For the driest and wettest events, human influence on the atmosphere has increased the odds about half of the area that has good data. In those areas, “the odds of the extremes are greater with global warming than without it,” he said. “One of the clearest signals that we do see is an increase in the odds of extreme dry events in the tropics,” he said.
The research also found that with the record low Arctic sea ice in 2012, “it would have been extremely unlikely to achieve the record-low sea ice extent without global warming,” Diffenbaugh said.
This study is another in the burgeoning field of extreme weather attribution.
After a record heat wave, deadly flood or devastating drought, questions inevitably arise about whether human-caused climate change played a role. Extreme event attribution tells us how much of the credit or risk for an event (or type of events) should go to global warming and how much should go to natural weather patterns or random climate variability, according to the National Oceanic and Atmospheric Administration.
In the past, scientists typically avoided linking individual weather events to climate change, saying the challenges of teasing apart human influence from the natural variability of weather. But that is changing.
“Over the past decade, there’s been an explosion of research, to the point that we are seeing results released within a few weeks of a major event,” said Diffenbaugh.
Columbia University climate scientist Adam Sobel, who wasn’t part of this study, called it “a step forward in that it allows general statements about what fraction of events of the given types selected have a statistically significant” human influence.
The methods used in the study, which appeared in the peer-reviewed journal the Proceedings of the National Academy of Sciences, could also be used to look ahead at predicted records in a warming climate, not just at historical records.