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NEI Viewpoint Discussion on Global Climate Change with Maureen T. Koetz
By Kevin Trenberth
Head, Climate Analysis Section
National Center for Atmospheric Research
Stories in the media about natural disasters have become common in recent years, whether it is the threat from hurricane Floyd along the Atlantic coast in September 1999, hurricane Mitch in central America in late October 1998, extensive flooding in China in 1998 and 1999, El Ni=F1o-related flooding in Peru or California in 1998, drought in the mid-Atlantic states in 1999, or many other weather-related disasters around the world.
What's going on? Are natural disasters occurring more often and with more devastation? Or is it merely that there are more cable television channels today and more competition to put something on the air? Certainly, there are more people who reside in coastal areas and flood plains and thus are more vulnerable to weather and climate fluctuations. Moreover, in several countries-such as China, Honduras and Nicaragua-deforestation and changes in land use have adversely altered how rainfall permeates into soils and runs off to cause flooding.
However, there also is clear observational evidence that the climate is changing in ways that lead to more social and environmental mayhem, and that human beings have a hand in the changes.
The Climate-Weather Connection How can climate changes affect the weather? After rain, when the sun comes out, the first thing that happens is the puddles dry up. Similarly, global warming from increases in greenhouse gases in the atmosphere not only increases surface temperatures but also enhances surface drying. The temperature increases also mean that the water-holding capacity of the atmosphere rises, too. And, together with the enhanced evaporation, this means that moisture amounts in the atmosphere should rise.
Observations confirm that atmospheric moisture has increased over the United States by about 10 percent in the past 25 years or so. Not only does this mean heavier rains (or snow), but it also means that naturally occurring droughts are likely to be exacerbated by enhanced drying. Droughts such as those set up by El Ni=F1o thus are likely to set in quicker and cause plants to wilt faster under a global warming scenario. Adding to the damage, droughts may become more extensive and last longer as a result of global warming. After all, once the land is dry, all the sun's heat goes into raising temperatures, bringing on sweltering heat waves that can cause problems for plants and animals alike.
Further, globally there must be an increase in precipitation to balance the enhanced evaporation. Observations show that over many parts of the world, including the United States, heavy rainfall events have been steadily increasing throughout this century. The net result is that when it rains, it pours harder than it would have under similar circumstances just a couple decades ago.=20
Going to Extremes So the question remains: Are we seeing more extreme weather events due to global climate change? Let me put it this way: floods that used to have an expected return period of 100 years may now recur in 50 or 30 years. The consequences include fewer gentle and beneficial rains for agriculture, more water damage to buildings and infrastructure, and more of the insect and disease outbreaks that often follow in the wake of floods.
So the best assessment of the global warming contribution to world weather patterns is that it is still small, but it is there and it may well be making weather extremes more extreme that they otherwise would have been. While some changes arising from global warming are benign or even beneficial, the economic affects of the weather extremes are substantial and clearly warrant further attention in national and international policy debates.
Atmospheric carbon dioxide concentrations stemming from human activities have increased by about 30 percent since the dawn of the industrial era. Global warming and associated climate change is expected as a result. The problem with this experiment is that if it turns out badly-however that is defined-we cannot undo it.
The wide range of natural variability associated with day-to-day weather means we are unlikely to notice most small climate changes except for the extremes. Human beings and other species are adapted to a range of natural weather variations, but it is the extremes that exceed our tolerances like the "straw that breaks the camel's back."
By George H. Taylor
State Climatologist for Oregon
President, American Association of State Climatologists
It's tempting to blame climate change for the multibillion-dollar consequences of floods, hurricanes, droughts, tornadoes, hail and thunderstorms. During the past 25 years, financial losses from these and other natural disasters in the United States have averaged about $500 million per week and are mounting.
Advocates of aggressive action to control global warming maintain that catastrophes will become increasingly likely if we do not take drastic steps to curtail fossil-fuel consumption and emissions of heat-trapping gases into the atmosphere. Vice President Al Gore, who keeps telling people that global warming is dangerous, attributed the devastating 1997 flood on the Red River in North Dakota and Minnesota to a combination of El Ni=F1o and climate change. Earlier this year, Gore said that record high temperatures provide "more evidence" that man-made, heat-trapping greenhouse gases are leading to long-term climate change.
It's true that human beings are producing more greenhouse gases now than before, and that greenhouse gases in the atmosphere are at higher levels than they have been for millennia. But much of the debate over global warming is really beside the point, because the key assumption-that there is a scientific consensus on climate change-is false. In fact, many mainstream scientists say there is insufficient knowledge of the magnitude of natural climatic variations, especially solar radiation and ocean currents, to gauge how large the human impact is by comparison.
Focus on the Weather, Not Warming The study, conducted by a panel of the National Academy of Sciences, shows a decrease in fatalities from extreme weather events such as hurricanes and floods during the past 20 years, yet an increase in property losses. The study found that sharply higher dollar losses in recent years were due in large part to demographic shifts. For one thing, there has been a steady migration of people to more vulnerable coastal areas as well as to more densely populated metropolitan regions, where even small storms can do major damage.
Human encroachment thus has reduced the ability of natural environmental systems to provide protection from extreme weather. Other contributing factors are the nation's population growth and the fact that per capita incomes are higher today than they were even two decades ago, making the potential losses larger.
The Real Issue: Insufficient Insurance Nationwide, only about 20 percent of the homes exposed to floods have flood insurance. Why? In part because many people assume that federal disaster assistance will function as a kind of hazard insurance, but such aid is almost always limited. And even when larger amounts are available, they are usually offered in the form of loans, not outright grants.
This suggests that the first priority-instead of continuing to debate the possible effects of global warming-should be adaptation, or developing strategies to cope with hurricanes, tornadoes and violent storms. The best way to reduce the risk of future catastrophes is for communities to take long-term, comprehensive looks at the dangers facing them. Communities that are built on flood plains, shorelines and other disaster-prone areas should decide what losses they are willing to accept, and devise suitable strategies to keep them within those limits.
The sooner people take responsibility for coping with natural hazards instead of hand-wringing over the presumed perils of greenhouse gases, the quicker the benefits in sustainable development and
disaster resiliency.
The inherent complexity of the global warming issue suggests that there might be greater benefit in mobilizing public and private resources to deal with extreme weather. A recent study bears this out.
One central problem is that the public increasingly looks to insurance to compensate for losses from many types of risk-taking behavior such as building homes, high-rise condominiums and office buildings on steep hillsides. However, the insurance industry already has problems providing coverage in areas subject to catastrophic losses because many insurers do not have the resources to pay for a worst-case event. And even when insurance is available, most property owners do not buy coverage against special perils, notably earthquakes and floods.