Climate Change Signal Emerges from the Weather
From Hawaii’s flurry of hurricanes, to
record high sea ice in Antarctica, and a
heat wave that cooked the Australian
Open like shrimp on a barbie, 2014
saw some wild weather. How much of
that was tied to climate change is what
scientists around the world tried to
answer in the Bulletin of the American
Meteorological Society’s annual
attribution report, which was published
Thursday.
What they discovered was that the
clearest impacts of warming could
be found in heat-related events, from
heat waves on land to unusually hot
ocean waters. Other events, like
droughts in East Africa and the Middle
East, California’s intense wildfires, and
winter storms that continually swept
across the eastern U.S., were harder to
pinpoint. In part this is because such
events are inherently complex, with a
multitude of factors influencing them.
For example, while the East African
drought was found to be both more
likely and more intense because of
warming, the situation in the Middle
East was less clear, with no discernable
climate change connection to the
various factors that influenced it.
Likewise, no direct push from climate
change could be found in California’s
wildfire activity, though it is clear that
it is increasing the overall wildfire risk
there.
And while some events, like the U.S.
winter storms and the record high
Antarctic sea ice extent, could be
pinned to a particular cause, that cause
could not be linked to climate change.
For other events, like the drought in
Brazil and flooding in the Canadian
prairies, humans influenced the
likelihood in other ways besides the
greenhouse gases that continue to be
emitted into the atmosphere.
What was clear, though, is that the fast-
growing field of what is called extreme
event attribution is gaining
momentum. Researchers are casting a
wider net for extreme events to
examine and continually refining their
methods. Attribution work has traveled
a considerable distance since its
inception just over a decade ago.“One thing we can say for sure: We
don't say ‘one can't attribute any single
event to climate change’ any
more,” Adam Sobel , an atmospheric
scientist who wasn’t involved with the
BAMS report, said in an email.
The BAMS special report was its largest
yet, with 32 studies looking at 28
different weather events from all seven
continents. The report also included
some types of events that didn’t appear
in the first three, including wildfires,
tropical cyclones and high ocean
temperatures.
“It’s a real achievement of the
scientific community,” said Noah
Diffenbaugh, a Stanford University
climate researcher who has conducted
attribution research but wasn’t
involved in this year’s BAMS issue.
“The report has garnered increasingly
broad interest and visibility over the
past few years. I'm sure that this
interest will only continue to grow,”
Jim Kossin, a co-editor of the issue, said
in an email.
As has been the case since the first
attribution studies, the firmest
conclusions about the role of warming
came from high temperature events.
Of the eight heat events examined—
including ones in Argentina, Australia,
South Korea, China and Europe—seven
were clearly made more likely because
of human-caused warming. (In the
eighth, the influence was uncertain.)
A May 2014 heat wave in Australia was
made 23 times more likely because of
warming, according to one of the BAMS
studies. In several of the events,
warming also made the heat waves
more intense.
