Teasing out trends in extreme weather and identifying global warming's fingerprint are challenging, acknowledges Thomas Stocker, an atmospheric scientist at the University of Bern in Switzerland and co-chair of the IPCC working group that reviews the state of climate science. By definition, extreme weather events are relatively rare and require observations – of consistent, high quality – over long periods of time and with “extremely good spatial coverage,” he says.
But enough data have been accumulating during the past 60 years at least to begin the process. The report examines observed trends for the nine weather and climate features it considered, the likelihood that global warming is evident in the trends, and projections of how those trends may play out through the end of the century.
Some of the highest confidence levels across these three categories are for trends in extreme temperatures, with somewhat lower confidence levels for extreme precipitation.
While uncertainties remain, many of the approaches communities and countries can take to adapt to weather extremes fall into what Chris Field, co-chair of a second IPCC working group that focuses on impacts of climate change, dubs “low regrets measures.” These measures will provide significant benefits regardless of the factors underlying extreme-weather events.
Indeed, the cost from extreme-weather events has been rising.
Between 1970 and 1989, losses from disasters of all sorts averaged about $5 billion a year globally, notes Mark Way, who heads sustainable-development efforts in the Americas for the reinsurance firm Swiss Re. Since 1989, losses have averaged some $30 billion a year, driven in large part by weather-related disasters. Last year, losses in the US hit $35 billion, more than half the $61 billion in losses from severe weather globally.
At this point, the increase in losses has more to do with rapid population growth and a build-up of wealth in some of the most vulnerable areas – along coastlines, for instance – than with global warming, both the IPCC report and Mr. Way note.