Extreme events show signal of climate change


CORVALLIS, Ore. – The rapid warming of Earth may not have directly caused all of the extreme weather events that have taken place in the past two decades – from the European heat wave of 2003 to Hurricane Katrina – but climate change has in some way had an impact on them, a new report concludes.

A 10-person committee of the National Research Council issued a report on Friday that examined the influence of humans on recent extreme weather events. Though the committee stopped short of saying that climate change is causing more frequent and severe events – a link difficult to prove in a short time frame – the connection, it acknowledges, is unmistakable.

“Scientists used to say that we can’t attribute any one event to climate change,” said Philip Mote, an Oregon State University climatologist and co-author on the report. “But that is a copout. Every extreme weather event has the fingerprint of climate change. The question is not whether global warming caused Hurricane Sandy; but rather how much stronger it was because of global warming.

“There is little doubt that Hurricane Sandy would have had less impact without climate change.”

The committee issued its report today in the National Academies Press, published by the National Academies of Science, Engineering and Medicine.

Humans’ use of fossil fuel since the start of the Industrial Revolution has begun to modify the Earth’s climate in many ways, said David W. Titley, who chaired the Committee of Extreme Weather Events and Climate Change Attribution.

“The consequences of this change to the climate are seemingly everywhere: average temperatures are rising, precipitation patterns are changing, ice sheets are melting and sea levels are rising,” Titley noted in the report’s preface. “These changes are affecting the availability and quality of water supplies, how and where food is grown, and even the very fabric of ecosystems on land and in the sea.”

Despite progress on understanding these changes, scientists are still trying many different approaches to understanding the causes of extreme events.

Since 2012, the number of research groups issuing studies on the attribution of extreme weather events has exploded, shedding new light on the external “forcing” mechanisms of events and how they are similar or different from other events.

This is allowing scientists to get a better feel for the impact of climate change on extreme events, Mote pointed out.

“The clearest tie between climate change and weather is in heat-related events,” said Mote, who wrote the sections on heat and drought in the report. “Droughts are getting worse and some aspect of every major heat-related event is stronger today because of climate change. In fact, most types of extreme events are getting stronger or more frequent, except those related to cold events, which are weaker or less frequent.”

Mote said he understands public skepticism over the link between global warming and weather in places like the East Coast of the United States, which has suffered through strong blizzards in the past two to three winters – a brief return to a climate of decades past. A warming planet does not affect every region uniformly, he added, nor does it make every season warmer than average.

On the other side of the country the three Pacific coast states – California, Oregon and Washington – experienced major drought in 2014-15.

“I’m frequently asked if we can expect more of the same in the future for the West Coast,” said Mote, a professor in OSU’s College of Earth, Ocean, and Atmospheric Sciences. “The answer is yes. The weather we had this past year, which was the warmest on record in Oregon, is the type of year we can expect to call ‘norm’ in the decade of the 2040s.”

College of Earth, Ocean, and Atmospheric Sciences

About the OSU College of Earth, Ocean, and Atmospheric Sciences: CEOAS is internationally recognized for its faculty, research and facilities, including state-of-the-art computing infrastructure to support real-time ocean/atmosphere observation and prediction. The college is a leader in the study of the Earth as an integrated system, providing scientific understanding to address complex environmental challenges