Warm Earth, Bigger Storms
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by Frank D. Roylance Baltimore Sun October 23, 2005
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This time it's Wilma, howling across the Gulf of Mexico toward a predicted landfall tomorrow on the southwest Florida coast, threatening residents still rebuilding from a battering by four hurricanes last year.
Wilma is this season's 21st named tropical storm and its 12th hurricane -- tying records on both counts. And No. 22 -- Tropical Storm Alpha -- formed yesterday afternoon.
Wilma is the third storm to hit the top of the hurricane intensity scale. Katrina, Rita and Wilma all reached Category 5 at sea, each with top sustained winds of 175 mph. That, too, appears to be an Atlantic basin record for one season. And it's not all hurricanes. Just this month, record early snows covered the Northern Plains, while a week of torrential rain flooded New Hampshire towns and threatened to burst a dam in Massachusetts.
Is this the stormy fate that global warming theorists have long warned about?
Most scientists say it seems to be. They can't say any particular storm is caused by global warming. But they are beginning to see its signature in a clear trend toward more extreme weather.
"Yes, global warming is happening, and the manifestations are now large enough that they're evident," said Kevin E. Trenberth, head of the climate analysis section at the National Center for Atmospheric Research (NCAR) in Boulder, Colo.
The toll of this year's barrage of violent storms from the tropics has been staggering.
Katrina was the costliest natural disaster in the nation's history, with some estimates exceeding $100 billion in damage. It killed more than 1,200, drowned New Orleans and erased entire Mississippi beach towns from the map. Rita killed more than 80 in Texas and Louisiana.
Hurricane Stan -- with only minimal hurricane winds -- packed rain that washed out entire hillsides in Central America, burying 2,000 Guatemalans in the mud.
Scientists say there's strong evidence that warming of the planet's oceans and atmosphere -- the result mainly of rising levels of manmade "greenhouse" gases -- increases the probability of extreme weather.
That means greater chances for heavy rain and snowstorms, more of the most intense hurricanes and more extreme heat waves and droughts.
That said, meteorologists never attribute a particular storm or heat wave to global warming. "For individual events, it will always be impossible to decide what it was due to," said Gabriele Hegerl, professor of earth and ocean sciences at Duke University.
She draws an analogy to smoking and lung cancer. Doctors can never say with certainty that an individual's cancer was caused by smoking. "But you can talk about what the probabilities are, and how they change. If somebody smokes, they are more likely to get lung cancer," she said.
Similarly, climatologists can only look at the data and say how much more likely an event such as the 2003 heat wave in France would be. That probability, Hegerl said, "has increased significantly due to global warming."
Trenberth warns that future weather looks worse than the present, so the public and policymakers must pay more attention to the storm warnings:
"A certain amount of institutional inertia [is] a key part of this problem. The key thing about global climate change is that the past is not as good a guide to the future as it has been."
The bottom line: Much of our national infrastructure -- levees, dams, bulkheads and drainage systems -- that was adequate in the past century might not be during this one.
Familiar mechanics The basics of global warming theory are simple enough, and familiar by now:
The rise of industrialization and proliferation of automobiles were made possible by the combustion of fossil fuels -- mostly coal, oil and natural gas. The end product carbon dioxide (CO2) is wafted into the air from smokestacks and tailpipes.
That has changed the composition of the atmosphere, with CO2 levels up 32 percent over the past 250 years. Ominously, scientists say, about half of that increase has occurred since 1970.
The problem? Although CO2 allows solar energy to pass into the atmosphere, it blocks heat from escaping back into space -- much like the glass in a greenhouse. Hence the "greenhouse effect."
The result, Trenberth said, has been an increase of the global mean surface air temperature measured at about 1.5 degrees Fahrenheit since the start of the Industrial Age. Nearly a full degree of that has been since 1970.
One degree might not sound worth worrying about, but "unfortunately, it doesn't work that way," said Greg Holland, a senior scientist at NCAR. The one degree of warming is a global mean -- an average of all daily highs and lows everywhere.
"It turns out the extremes are what defines the temperature," he said. And the local extremes people experience might be dangerously higher. For example, the 100-degree summer day of 30 years ago could become a 110-degree day 50 years from now.
"A few degrees make a big difference in the impact on everything, including people," Holland said.
Global ocean temperatures are also rising. And as the waters warm up, they expand and sea levels rise. Melting glaciers and ice shelves add about one-third of the total increase.
"Some of the most spectacular evidence has emerged since 1992," Trenberth said, with sea levels increasing by 1.3 inches over 12 years.
Compared to the leisurely pace of earlier change, he said, "that's a lot."
Holland said conservative projections hold that global sea levels will rise 3 feet to 4 feet by the end of this century. Added to storm surges, that presents "a significantly worse scenario in terms of the vulnerability of coastal communities."
That vulnerability is exacerbated by rapidly increasing coastal population and development.
Skeptics argue that the global warm-up is more likely part of a natural cycle, influenced by solar cycles or other natural changes. Most climatologists say the data show that that might have been true in the first part of the 20th century, but not any longer.
They tackled the question with supercomputers and climate "models." These ultra-complex computer programs crunch vast quantities of weather and climate data through mathematical formulas that describe the interactions of the oceans, the atmosphere and such factors as solar cycles, snow and ice cover, and volcanic eruptions.
Scientists can then run climate simulations -- manipulating one variable at a time -- to see which influences match up best to real observations.
More and more, they say, those calculations show the temperature gains of the past half-century come from human activity -- mainly greenhouse gases.
"I think this is a fairly well-accepted result, mainly because it has been reproduced now by a lot of different models," said Jerry Meehl, senior scientist at NCAR.
Although the Bush administration campaigned to discredit the notion of global warming during its first four years, the president recently conceded that something is amiss.
"I recognize that the surface of the Earth is warmer and that an increase in greenhouse gases caused by humans is contributing to the problem," he told reporters at a Group of Eight summit in July.
But he has rejected the Kyoto Protocol, an international agreement that would limit greenhouse gas emissions.
Worrisome forecast For most of us, the chief concern about rising air and ocean temperatures, of course, is their impact on weather. The forecast is worrisome.
When scientists run their best climate models using continued greenhouse gas emissions, they see more extreme weather.
And again, it's a fairly simple mechanism, Trenberth says: For every degree of increase in the temperature, the atmosphere's capacity to hold moisture increases by 4 percent. And satellite measurements since 1988 have confirmed a 4 percent increase in water vapor over the globe's oceans, providing both added moisture and heat energy for any storms that form.
Overall precipitation in the United States increased 7 percent during the past century, mostly east of the Rockies, Trenberth said. The heaviest rainfalls dropped 14 percent more water.
Heavier precipitation will have a greater chance of overwhelming dams, levees and drainage systems built to standards that never took global warming into account.
"Our systems are just not designed to accommodate this extra stuff," Trenberth said.
Global warming theory also predicts an increase in the number of intense hurricanes around the world -- Categories 4 and 5 on the Saffir-Simpson scale.
And a study published in the journal Science in September by NCAR's Holland and Judith Curry reported just that -- a shift toward the more-intense storms, which increased by 80 percent between 1975 and 2004.
Not everyone blames this year's record-tying activity in the Atlantic basin on global warming. The National Hurricane Center and Colorado State University's William M. Gray insist it can be explained by a shift in a well-known cycle of ocean and atmospheric conditions that began in 1995.
Others, including Trenberth, say global warming is likely being superimposed over regional climate variability in the Atlantic, producing storms that are "a little more frequent and more intense."
Global warming theory also predicts more extreme heat waves and droughts. "Extra heat trapped in the system has to go somewhere, and it causes drying in places where it hasn't rained," Trenberth said. "Plants wilt, and the risk of fire goes up."
In the summer of 2003, France experienced the worst heat wave in its history. An estimated 30,000 people died. This past summer, Spain and Portugal suffered record droughts, and two dozen firefighters died fighting huge wildfires.
The longevity of CO2 in the atmosphere and the slow temperature response of the oceans mean that the warming effect will continue for decades. Even if lawmakers begin to curb emissions, the benefits will accrue to their grandchildren.
Meehl said the public and lawmakers lag behind most scientists on the importance of global warming because the news media usually quote skeptics, which leaves the impression this is unsettled science.
There is still plenty of scientific debate over details -- over how great the changes are, how fast they're occurring and how "feedback" mechanisms, such as cloud cover and carbon uptake in the oceans and forests, affect the speed of change.
There's debate over how accurate various climate models really are, and over how much greenhouse emissions and CO2 concentrations will change over the years.
Holland said a few scientists and others, whom he calls "belief doubters," simply "find every reason not to accept" global warming in spite of the evidence.
But these are a diminishing minority.
"Twenty years ago, I was on the skeptics' side," Holland said. But after years of rigorous scientific debate, the evidence has piled up in scientific literature, he is a convert: "If you can't find too many things wrong with it, it's probably right. That's what science is about."
Photo: http://www.bay13.net/
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Source: Baltimore Sun
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