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Weather or Not?

Extreme Weather Events and Climate Change

Ellie M. Cohen

Record-breaking weather seems to be the norm these days. Here in the San Francisco Bay Area, we experienced record cold temperatures on Saturday, November 21st, followed only eight days later by record high temperatures. An early-October storm more than doubled the previous rainfall record for that date, set in 1957. In mid-May 2008, a record-breaking heat wave caused sea-surface temperatures at NOAA's Bodega Bay buoy to rise by 10˚ F in 24 hours and distressed breeding seabirds on Alcatraz and Southeast Farallon islands (see page 4 ).
Droughts and floods are among the extreme events now posing increasing challenges. Flickr photos.

These recent extremes are not limited to the Bay Area, of course. The most severe multi-year drought in over 100 years in the Southeast was followed by the greatest deluge on record in Georgia, in September 2009. A USGS scientist reported that "this flood was off the charts." The chances of a flood of that magnitude were much less than one in 500 and virtually impossible to predict based on the century of weather data that we have (Science Daily, November 9, 2009).

Warmer air holds more water vapor, so as the planet heats up—the first decade of the 21st century was the warmest on record—more intense precipitation events are likely. Even extremes in snowfall are being seen around the world. For example, the December 19, 2009 storm in the mid-Atlantic region broke records for the most snow to fall during a single December day. At Baltimore-Washington International Airport, 20.5 inches were recorded, smashing the previous record of 6.8 inches in 1948.

And a new study from Oregon State University concludes that the maximum height of extreme ocean waves in the Northwest has grown significantly in recent decades, with enormous potential consequences for coastal ecosystems.

As this Observer highlights, PRBO scientists have documented numerous bird responses to extreme weather events. We often discuss how these might be driven by natural variability and/or human-caused global warming.

The United States government's Global Change Research Program, in its July 2009 report to Congress, Global Climate Change Impacts in the United States (, concludes that average global temperature increases over recent decades are due primarily to human-induced emissions of heat-trapping gases, and that climate changes are accelerating in the U.S., with more frequent and intense extreme weather events, such as record-breaking rainfall, heat waves, drought, and flooding. The report states that "extreme weather and climate events are among the most serious challenges to our nation in coping with climate change."

Major insurance corporations are coming to similar conclusions. Munich Re, the world's largest reinsurance company (with gross sales of $38 billion in 2008), warned in their recent annual report that climate change remains a threat in 2010 and the decades to come, adding that the failed Copenhagen summit is bound to make insurance costs rise in the future. They found that "severe weather events accounted for 45%, or nearly half, of global insured losses" in 2009, and that "the trend toward an increase in weather-related catastrophes continues...." (Wall Street Journal, December 30, 2009)

We now know unequivocally that birds, other wildlife, and human communities across the world are seriously threatened by these accelerating changes.

A priority recommendation of the U.S. Global Change Congressional report is a significant expansion of "global impacts science." PRBO is uniquely poised to contribute to this emerging field, to help society understand, reduce, and adapt to the impacts of our rapidly changing climate—ecologically and economically.

Ellie M. Cohen is PRBO's President and Chief Executive Officer.

Extreme Weather Info

Are you interested in knowing more about weather extremes and climate change? Below are just some of the sources that PRBO staff are reading and discussing.

Weather and Climate Extremes in a Changing Climate is a four-page summary of frequently asked questions, published in 2008 by the U.S. Global change Research Program.

The U.S. Global Change Research Program offers excellent scientific assessments on a range of topics, including extreme weather.

ScienceDaily provides free daily and weekly email news summaries, by topic—Earth & Climate, Environment, Plants & Animals, etc. Sign up at

Real Climate offers commentary on climate science for the interested public from working climate scientists.

Climate Witness, from World Wildlife Fund, offers stories from people around the world about how climate-change now affects their lives.

Conversations With the Earth is helping indigenous groups document threats they already face from severe weather and a changing climate.