Manmade global warming is causing up to a tenfold increase in the risk for prolonged and severe heat waves, and is influencing other extreme weather and climate events, a slew of new studies found.
In a collection of 22 peer-reviewed analyses on 16 extreme weather and climate events during 2013, which were published Monday as a nearly 100-page report, international teams of scientists found clear ties between global warming and extreme heat events from Australia to China, and some signs of ties between the record California drought and global warming as well.
In all, nine of the 16 extreme events were attributed at least partially to manmade global warming.
The report amounts to the most ambitious attempt yet to put extreme events, such as floods and severe storms, into a long-term climate change context using methods known as “extreme event attribution.”
Global warming contributed to the baking of Australia, Korea, Japan and China
Of the 10 studies on heat waves that are included in the lengthy report, all five found clear ties between the events and global warming. For example, a study on extremely hot temperatures in Korea during the June through August 2013 period, found that manmade global warming — which has raised average surface temperatures — has made heat waves there up to 10 times more likely. In 2013, Korea had its hottest summer nights and second hottest days since 1954, the study said.
Another study found that global warming “played a significant role” in raising the chance of events such as the heat wave in Japan in 2013, during which 143 locations broke their daily average temperature records. Other studies tied global warming to increased odds of heat waves in eastern China, Europe and Australia.
Regarding the heat in Australia, where the Bureau of Meteorology was forced to add a new color to its weather maps to show extremely hot temperatures up to 129 degrees Fahrenheit, the studies showed extremely low chances that the heat could have occurred without manmade global warming. One of the studies found the percent of risk of the event that could be attributable to manmade global warming to be “essentially 100%.”
“The results from the Australian studies are rather striking,” said Peter Stott, the leader of the climate assessment team at the UK Met Office in Exeter, England.
Stott said the evidence shows that “it’s very hard to imagine how you could have had those temperatures without global warming.”
September 2013 was the hottest September on record in Australia
September 2013 was the hottest September on record in Australia, and one of the studies found that the risk of such heat in September has jumped fivefold due to manmade climate change.
Scientists gain confidence in conclusions about extreme events when multiple studies use different methods, while arriving at similar conclusions. Five independent research teams looked at different factors related to the record heat in Australia in 2013, and each team came to the separate conclusion that human-caused climate change increased the likelihood and severity of that event. This raises scientists’ confidence that global warming made the prolonged heat wave in Australia much worse.
“The evidence in the Australian papers is extremely strong,” said Martin Hoerling, a researcher at the National Oceanic and Atmospheric Administration (NOAA) in Boulder, Colorado, who was not involved in that research.