Like That Heat Wave? 75% of Them Attributable to Climate Change

(Bloomberg) — Blame global warming for about 75 percent of
the world’s unusually hot days and 18 percent of its extreme
snow or rain, according to a new paper in the journal Nature
Climate Change.

Heat waves and heavy storms are occurring at least four
times more often than they did before carbon pollution started
driving up thermometers. Global average temperatures are now
about 0.85 degrees Celsius (1.4 Fahrenheit) higher than before
industrialization.

Additional heat and precipitation are expensive. Severe
weather costs the U.S. economy as much as $33 billion a year,
according to a U.S. Energy Department report released April 21.

And those figures will increase as the planet continues to
warm, as climate change may not be smooth or gradual, according
to the new paper. At 2 degrees Celsius — United Nations climate
negotiators’ avowed upper limit — extremely hot days may be
twice as likely as at 1.5 degrees Celsius of warming. After 2
degrees Celsius, the odds of high-heat days may be five times
greater than today.

“What used to be a one-in-a-thousand day, a one-in-three-year event, actually occurs four times in three years,” Erich
Fischer
, a researcher at the Institute for Atmospheric & Climate
Science in Zurich and one of the study’s authors, said in a
telephone interview. “Weather extremes have always been
occurring, before any human influence, but that doesn’t mean
that there can’t be human influence on the extremes.”

Scientific Consensus

There is widespread scientific consensus that human
activity is causing climate change, which President Barack Obama
said “can no longer be denied” while visiting the Florida
Everglades last week.

Fischer and colleague Reto Knutti examined more than a
century’s worth of data using more than two dozen climate
models, running simulations that account for rising greenhouse-gas emission levels through the year 2100. Fischer was quick to
emphasize the global nature of their results. The study is
confined to heat and precipitation. How might evolving
conditions affect meteorological events like tornadoes or hail?
“We do not agree how they change,” he said.

Global warming’s responsibility for the world’s heavy
rainfall may increase from 18 percent today to 40 percent if
temperatures rise by 2 degrees Celsius.

The authors said that their results may be of use to policy
makers, by sharpening their understanding of risk as climate
change worsens. “With every degree of warming,” they wrote,
“it is the rarest and the most extreme events — and thereby
the ones with typically the highest socioeconomic impacts — for
which the largest fraction is due to human-induced greenhouse
gas emissions.”

Translation: The worse things get, the more we’re bringing
it on ourselves.

To contact the reporter on this story:
Justin Doom in New York at
jdoom1@bloomberg.net

To contact the editors responsible for this story:
Reed Landberg at
landberg@bloomberg.net
Will Wade, Robin Saponar

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