Are extreme weather and global warming linked?

Maybe. But maybe not. Scientists say not enough evidence exists to blame global warming for the recent heat waves and flooding seen around the world.

The headlines this summer seem ominous:

"Extreme Weather Plagues Globe in 2007".... "Across Globe, Extremes of Heat and Rain".... "Insurers Claim Global Warming Makes Some Regions Too Hot to Handle".... "Floating Arctic ice shrinking at record rate".... "The World Meteorological Organization reports on extreme weather and climate events."

But is global warming to blame? Maybe. Maybe not.

In any case, reports the World Meteorological Organization, "Weather and climate are marked by record extremes in many regions across the world since January 2007."

"In January and April 2007 it is likely that global land surface temperatures ranked warmest since records began in 1880…. [It is] very likely that hot extremes, heat waves and heavy precipitation events will continue to become more frequent."

"The agency found that climate warming was unequivocal and most likely 'due to human activities such as the burning of fossil fuels'," reports CNN.

Among the evidence cited by the UN's meteorological agency, according to CNN:

"Four monsoon depressions, double the normal number, caused heavy flooding in India, Pakistan and Bangladesh…. England and Wales have experienced their wettest May-to-July period since record-keeping started in 1766…. Late last month in Sudan, floods and heavy rain caused 23,000 mud brick homes to collapse, killing at least 62 people…."

Meanwhile, reports the BBC, "Arctic sea ice is expected to retreat to a record low by the end of this summer."

Citing measurements from the US National Snow and Ice Data Center (NSIDC), the BBC reports that this summer is likely to end with the lowest ice cover on record.

"If you look at data for the first week in August, we are way below what we saw in 2005," explained Mark Serreze, a senior research scientist at the NSIDC. "So unless something really changes, for example the Arctic suddenly becomes a lot colder, it is going to be hard not to beat the previous record."

But as Agence France-Presse reports, one summer of bumptious weather does not confirm global warming.

"…establishing a link between climate change and extreme weather is a controversial matter…. scientists caution there is not enough evidence to blame global warming for recent extreme weather, and there are those who say there is no proof that extreme weather events are becoming more frequent."

Last week's storm that drenched New Jersey and then pounded New York City, for example, "was strong but not particularly rare for a hot summer day," Pennsylvania State University meteorologist Jeff Warner told the Associated Press.

"Climate scientist James Hansen, director of NASA's Goddard Institute of Space Studies, agreed: 'You cannot blame a single specific event, such as [last] week's storm, on climate change,' he said. 'However,' he added, 'it is fair to ask whether the human changes have altered the likelihood of such events. There the answer seems to be 'yes.' "

Experts often point out that long-term climate and short-term weather (which may be affected by other natural events, such as sea temperature and El Niño) are not the same. With climate, the longer view is more important. Citing a new study from Britain's Met Office, MSNBC reports that "Global warming will slow during the next few years but then speed up again."

"There is ... particular interest in the coming decade, which represents a key planning horizon for infrastructure upgrades, insurance, energy policy and business development,' Douglas Smith and his co-authors noted. The real heat will start after 2009, they said."

Speaking of insurers, generally a conservative lot when it comes to figuring the odds of having to pay claims, Scientific American warns that "as the nation braces for an active hurricane season, private insurers jump ship, leaving federal and state governments liable for ever increasing payouts."

"If circumstances change due to global warming that alter the level of risk, insurance companies need to be free to reflect that risk," says David Snyder, vice president and assistant general counsel for the American Insurance Association (AIA). "The reality is that in some places the risk is so severe that [these locations] are uninsurable."
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