Big, wet storms may become new 'normal'
December 06, 2007
The Oregonian
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Global warming - Faster-than-expected tropical expansion could bring more tempests to the Northwest
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The steamy tropical belt around Earth's midsection, birthplace of the powerful storm that pounded the Northwest this week, is expanding much faster than scientists studying global warming expected.
It's now as wide as climate models suggested it would be at the end of this century, new research shows. The rapid growth is another sign that bigger storms carrying more rain may become the new "normal" in the Northwest, especially in fall and early winter.
Because the tropics drive much of the world's weather, the new research suggests that its growth could cause major shifts that further dry out arid regions such as the Southwest United States and direct more intense storms toward the Pacific Northwest.
"If it continues at this pace, it will be a very big deal," said Qiang Fu, a professor of atmospheric sciences at the University of Washington and an author of the research published this week in the scientific journal Nature Geoscience.
Government and business leaders in the Northwest say the region must begin adjusting to a warmer, stormier world -- and taking steps to avoid the havoc wreaked by this week's storm.
Repeated storms such as the pounding rainstorm that ripped apart roads in November 2006, a powerful windstorm last December and the one this week could make insurance companies wary of issuing policies in the Northwest, said Mike Kreidler, Washington's insurance commissioner.
The region already faces earthquake and tsunami risks, said Kreidler, co-chairman of a task force on global warming for the National Association of Insurance Commissioners.
If climate change amplifies weather damage, he told Congress this year, the region could find itself in a situation similar to that of the hurricane-prone Gulf Coast. After Hurricane Katrina, property insurance there became expensive, if not impossible, to get.
Should we rebuild here?
The Northwest must strengthen building codes to make sure homes and other structures avoid danger from wind, flood and wildfires, Kreidler said. "We also need to take a careful look at where we develop and redevelop our communities. We need to first ask ourselves, 'Is the risk so great from some perils we should not build here?' "
Rex Burkholder, a Metro councilor, said that question comes to mind when he sees pictures of coastal Tillamook flooded by overflowing rivers during severe rainstorms -- as it has been twice within little more than a year.
"Should these people be rebuilding?" he said. "Is it time to say, 'Let's move them out. Let's get them to higher ground so this doesn't keep happening?' "
Construction and development must take into account higher risks of flooding and other extreme climate events, said Burkholder, who serves on a task force Gov. Ted Kulongoski formed to look at ways of adapting to climate change.
Highway engineers are beginning to consider new alignments of the highway around Mount Hood after a big storm in November 2006 severed it in several places. Debris loosed by faster melting glaciers worsened the damage.
Insurers recently approached scientists at the University of Washington's Climate Impacts Group about assessing the risks of climate change in the Northwest, said Edward Miles, a UW professor and leader of the group. That's a positive sign, he said, highlighting new attention to the risks of global warming.
But scientists walk a tightrope when it comes to global warming. Many are convinced that the region must adjust to it, but they can't prove that it's responsible for any single weather disaster, such as this week's storm.
The global weather system is simply too complex.
"It's too soon to say, 'Definitely,' " Miles said. "But it's not too soon to be planning on this basis."
Warming brings storms
What scientists can say is that they expect storms such as this week's to become more common and perhaps more intense. The Earth is warming, and warmer air holds more moisture, which supplies the raw fuel for major storms.
Heavy rain and snowfall have become more common across the country, according to a report released Wednesday by Environment America, a nonprofit group that advocates reducing greenhouse gases. The trend was especially strong around Seattle.
Oregon -- especially southern Oregon around Medford -- was an unusual exception to that finding, though, with a negligible or decreasing trend in heavy precipitation.
The growth of Earth's tropical belt, generally depicted on maps as the area between the Tropic of Cancer and the Tropic of Capricorn, puzzles scientists because it has happened so quickly.
Climate models predicted that the generally warm, humid belt near the equator would expand as greenhouse gases increase and temperatures rise. But studies now show that in the past 25 years it expanded toward the poles at least four times faster than the models suggested it would over the next century.
Scientists don't know why it has grown so much. Global warming may be a factor, but changes in the ozone layer, natural climate variations such as El Nino and warming sea surface temperatures also might play a role.
An expanded tropics pushes the jet stream and storm tracks that affect the Northwest farther north. That could bring more storms to the region. It also provides more ground for tropical storms and typhoons to form and build up.
"The total energy in the system is greater, that's for sure," Fu said.
The storm that struck the Northwest this week drew its initial energy from a pair of tropical typhoons and gained force as it clashed with cold Alaskan air over the Pacific.
Michael Milstein: 503-294-7689; michaelmilstein@ news.oregonian.com For more environment news, go to http://blog.oregonlive.com/pdxgreen
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