The Heat Is Online

New findings link warming to specific weather events

‘Human fingerprint’ seen on certain weather events

The Associated Press, March 12, 2016
WASHINGTON — Climate science has progressed so much that experts can accurately detect global warming’s fingerprints on certain extreme weather events, such as a heat wave, according to a high-level scientific advisory panel.
For years scientists have given almost a rote response to the question of whether an instance of weird weather was from global warming, insisting that they can’t attribute any single event to climate change.
But ‘‘the science has advanced to the point that this is no longer true as an unqualified blanket statement,’’ the National Academies of Sciences, Engineering and Medicine reported.
This new field of finding global warming fingerprints is scientifically valid, the academies said in a 163-page report released Friday. The private nonprofit has advised the government on complex, science-oriented issues since the days of Abraham Lincoln.
When it comes to heat waves, droughts, heavy rain, and some other events, scientists who do rigorous research can say whether they were more likely or more severe because of man-made global warming, said academies report chairman David Titley, a Pennsylvania State University meteorology professor.
‘‘While we plan for climate, we live in weather,’’ Titley, a retired Navy admiral, said in an interview. ‘‘These extremes are making climate real when in fact they are attributable to climate change.’’
Not all weird weather can be blamed with any degree of certainty on global warming, according to the report. ‘‘For a certain class and type of event there is a human fingerprint,’’ said report coauthor Marshall Shepherd, a University of Georgia meteorology professor.
The report says there is ‘‘high confidence’’ in studies looking for climate change connections between extreme hot and cold temperatures, such as the Russian heat wave of 2010. There’s medium confidence in efforts trying to attribute droughts and extreme rainfall.
Hurricanes and other tropical cyclones, wildfires, and severe thunderstorms are on the low end of the confidence range, the report found.
In some cases heat and lack of rain combine and the studies find a viable connection to global warming, such as in the recent four-year California drought and the drought that hit Syria and neighbors, Titley said.
‘‘The fog of uncertainty that obscured the human role in individual events is finally lifting,’’ said Princeton University professor Michael Oppenheimer. He wasn’t part of the study, but is on the board of Climate Central, which manages a large climate attribution project.
Good attribution studies are based on what Titley calls a ‘‘three-legged stool’’ of observational records of decades of past events, detailed understanding of the physics that cause the weird weather itself, and sophisticated computer models that simulate the chances of the extreme event if there were no man-made, heat-trapping gases warming the atmosphere.