The risks of disrupting climate.

In ancient civilizations, questions of future risk were usually left to soothsayers. With the modern analytical tools of risk management, we've come a long way in shaping our fate. Does it make sense to throw those tools aside in the face of climate change?

Las Vegas and Monte Carlo, with their myriad roulette wheels and blackjack tables, are famed gambling meccas. Kyoto, Japan is not. Glitzy casinos cannot be found in Kyoto, center of Japanese culture since the late eighth century. The streets are lined instead with manicured gardens, ancient Buddhist temples, and Shinto shrines. But before the end of the year, Kyoto may become the site of a huge, high-stakes gamble. In December, the city will host a critical meeting of the parties to the 1992 United Nations Framework Convention on Climate Change. Delegates from 166 countries will address some of the largest risks the world has ever faced: the potentially catastrophic consequences of global climate change.

On the eve of the Kyoto conference, the Earth is experiencing a twentieth century warming trend. As economies around the world have industrialized, they have been powered by fossil fuels. Ever greater burning of these fuels and ever faster rates of deforestation have released precipitous increases in carbon dioxide. Along with other "greenhouse" gases, carbon dioxide traps heat, enhancing the natural greenhouse effect of the Earth's atmosphere. Continued, unrestrained emission of these gases, most scientists agree, will invite large-scale climate disruption (see box, page 12).

Already, phenomena consistent with an enhanced greenhouse effect abound. Polar ice shelves are cracking and splintering, and mountaintop glaciers around the world, from the Alps to the Andes, are in retreat. Temperature-sensitive coral reefs are bleaching under stress, the timing of seasons has changed, and the geographic range of optimal temperature for various plants, animals, and disease vectors has shifted (see map, pages 14-15). In theory, there is a small chance that this warming falls within the climate's natural variability. But it would be dangerous for the envoys sent to Kyoto to bet on that chance by allowing nations to maintain or accelerate their emissions of greenhouse gases. The resiliency of nature, availability, of food and water, health of human populations, and vibrancy of economics all hinge on climate. As Stanford University climate scientist Stephen Schneider puts it in his new book, Laboratory Earth, continuing to alter the climate at the current rate is akin to taking a "planetary gamble we can't afford to lose."

As gamblers, human societies have become ever more adept at working the odds. In fact, it was casino-style gambling that led us to the tools we now use to assess many risks. During the mid-seventeenth century, mathematician Blaise Pascal and lawyer-turned-math enthusiast Pierre de Fermat - actual Renaissance men - teamed up to calculate the odds in a game of chance. In doing so, they developed an important mathematical idea, one that is the basis for our modern concept of risk: the theory of probability. Peter Bernstein, author of Against the Gods: The Remarkable Story of Risk, describes risk as "the revolutionary idea that defines the boundary between modern times and the past... the notion that the future is more than a whim of the gods." Although many early peoples, such as the ancient Greeks, had mathematical skills, they did not apply them to predicting the future; for them, the future was the sole province of the oracles.

Today, however, a mathematical appraisal of the odds often informs our plans for the future. Assessment of risks helps patients to decide on surgery, investors to buy stocks, and military advisors to devise defense strategies. Modern patients seek explanations of medical conditions that are couched in probabilities: what could the worst outcome be? Is it more risky, to have surgery or to forego it? When faced with a range of potential outcomes - in health care, engineering, finance, defense, or any other field - we have learned to weigh risks, in order to ignore the small dangers and hedge against catastrophe. To underscore this point, a managing director at the large investment bank Morgan Stanley reportedly likes to quote J.R.R. Tolkien: "It doesn't do to leave a live dragon out of your calculations if you live near him."

Potentially severe climate disruption is a lurking "dragon" that we must now include in our future planning. For instance, we must realign the energy industry if we are to see a reduction in the burning of fossil fuels. If the envoys in Kyoto choose to do so, they can improve the odds of the current climate "gamble." By agreeing to a legally binding climate treaty protocol with strict targets and timetables, they could produce perhaps the most important risk management strategy of the next century. In fact, dealing with the uncertainties of climate change in the twenty-first century may assume the same overiding importance as has military planning in the twentieth. Governments are spurred to build defense capacity not by the knowledge of certain conflict, but by the risk of war. It's the same kind of thinking that we use on a personal level, when we purchase car insurance. We know we might never have a car accident, or have only a small accident with minor costs. But, recognizing that we could total the car, or be found liable for a catastrophic injury, we buy the insurance to avoid financial ruin. Diplomats in Kyoto will have the chance to agree on some form of "insurance" too - but in their case the entire planet stands to lose from a "crash." These envoys will be crafting insurance not just for the citizens of their home countries, but for those without a seat at the bargaining table, including future generations.

As the Kyoto conference approaches, some skeptics continue to focus on a single question: "Is climate change real?" In doing so, they purposefully misguide public debate. The majority of scientists have agreed that climate change is real, but they also agree that the local effects of climate change are highly uncertain. Therefore, among the questions we should be asking are: "What do we know about the risks?"; "What level of risk is acceptable?"; and "How can we avoid unacceptable risks?" Even British Petroleum, a corporation that mines the fuels that stoke greenhouse warming, has recognized the importance of asking such questions. In explaining BP's decision to move into climate-friendly solar technologies, chief executive John Browne conceded in May 1997 that the grave risks of climate change "cannot be discounted."

Learning to Assess Climate Risks

If we approach climate change as we do other risky situations, then our first step is to systematically identify the range and probability of possible outcomes. For instance, companies that sell car insurance classify the riskiest clients - say, male teenagers who drive sportscars - by studying historical data on car crashes. Large investors, trying to ascertain the risks of investing abroad, consult Institutional Investor's country credit ratings, based on the economic, financial, and political risks in a given country. The closest analogue for climate change is the rapidly growing body of relevant scientific research, which is continually reviewed by a global network of climate experts. This group, the Intergovernmental Panel on Climate Change (IPCC), was created in 1988 by the World Meteorological Organisation and the United Nations Environment Programme to help decisionmakers around the world understand the scope of the climate change problem.

The IPCC has been as methodical as any actuary or financial analyst in its step-by-step approach to studying climate change. The scientists first examined the range of projections for future population growth, economic development and technological innovation - the key trends that will influence our emissions of greenhouse gases in the future. then, translating these scenarios into possible levels for carbon dioxide concentrations, the scientists determined. that we can expect to see at least a doubling of preindustrial levels of carbon dioxide by the middle of the next century. Consensus is that this doubling will raise the average global surface temperature 1 to 3.5 [degrees] C by 2100. This change far exceeds any recent natural fluctuation and will occur at a rate faster than any since the last Ice Age more than 10,000 years ago.

Climate is weather averaged over the long term: decades, centuries, and millennia. It is a tremendously complex system that comprises not only the atmosphere, but also the oceans, ice, the land and its features, as well as rivers, lakes, and sub-surface water. The Sun's output, the Earth's rotation, and the chemical composition of the atmosphere and ocean all affect this system. Changes in any of these internal or external factors are responsible for the climate's variability. While the climate has undergone some wild shifts over the course of geological history, it has been relatively stable during the period in which modern human society has evolved.

With the warming that is projected from the gases that humans are adding to the atmosphere, this stability may come to a man-made end. Sea level is expected to rise between 15 and 95 centimeters over the next century as oceans expand and ice melts. The largest rises in temperature will occur at higher latitudes. Higher temperatures will enhance evaporation and precipitation, altering the global cycling of water. Some areas will become wetter while others become drier. And dramatic events such as floods and storms could become more variable.

These changes may occur faster than we will be able to respond. And because both nature and climate are so complex, we may be startled by some unwelcome "surprises." For instance, climate change could magnify other global problems that stem from a larger human population. Even as average temperatures are rising, we expect to see human population rocketing from 6 billion today to 9 billion within the first half of the next century; ever greater numbers of rural dwellers migrating to urban areas, especially coastal cities; and the use of land rapidly changing - as, for example, in the conversion of forests to farmland. In concert with soil erosion, water and air pollution, and a host of other ills, climate change could push ecosystems past tolerable thresholds. These unhealthy combinations, or "synergisms," may already be spurring events such as the worldwide decline of various animals, the large-scale growth of toxic algae, and the death of coral reefs. Moreover, the warming we cause may trigger more warming, spinning the climate into an inhospitable state. Climate operates over such a long time scale that adverse consequences may take centuries or millennia to reverse. Other changes, such as the decimation of species, are likely to be irreversible. Such surprises may be our greatest risk, the equivalent of the financial catastrophe we try to avoid by buying insurance.

The Stakes

Surprises, by their nature, are difficult to foresee, but many simpler, "linear" responses to climate change are the subject of intense study. Looking to clues from history, current observations, and lab and field studies, scientists have begun to suggest how projected changes (i.e. temperature increases, sea-level rise, and variation in the global cycling of water) might affect nature, food production, water availability, human health, coastal areas, and other systems vulnerable to the vagaries of climate.

For instance, the icy Antarctic ecosystem is particularly sensitive to warming, as the story of the South Pole's Adelie penguins suggests. Midwinter temperatures have risen 4 to 5 [degrees] C on the western Antarctic Peninsula over the past five decades. University of Montana ecologist William Fraser has studied the Adelie penguins for 22 years, has seen their population drop 40 percent, and thinks that warmth could be causing changes that make it hard for penguins to find food and breed. The Adelie normally feast on a shrimp-like creature called krill, found in plankton-rich areas near sea ice. But increases in Antarctic temperatures have melted sea ice, apparently causing krill populations to plummet. In addition, increased spring snowfall, as a result of warmer, moisture-laden air, may be thwarting the penguins' attempts to breed. Their eggs may be getting buried under snowbanks. Scientists agree that the penguins' home is likely to be one of the first spots on Earth to feel a temperature hike. Thus, the plight of the penguins could be a small, early example of changes we may begin to see on a much larger scale.

Consider the fate of the world's plants, which are all adapted to certain ranges of temperature and moisture. Entire ecosystems could unravel if changes in climate force plants out of their current ranges. Over time, the population of a plant species can move, as seeds, dispersed by winds and animals, take root in a more hospitable habitat. While past changes in climate forced plants into different geographic ranges, those prehistoric plants did not have to contend with urbanized landscapes. Today, temperature shifts, combined with fragmented habitat, could strand many plants in regional pockets and consign others to extinction. A Dutch study suggests that major vegetation changes will take place by 2050 in 24 percent of the world's parks and protected areas. In some cases, park boundaries may eventually undermine the protection of some species, as roads, farms, and urban areas prevent species from moving.

If warming trends persist in mountain ecosystems, for instance, plants that are adapted to warm conditions may gradually move toward summits, and colder-weather varieties could be caught in shrinking ranges. Already, ecologists at the University of Vienna have found that plants have been "climbing" the Alps as fast as 3.7 meters per decade over the past 90 years. In the U. S. Yellowstone National Park, University of Oregon researchers concluded that warming projected by the IPCC could cause the range of high-elevation trees, including several species of pine, to decrease to such an extent that the trees will not be able to survive. The rate at which we continue to emit greenhouse gases will influence the speed of climate change - and a fast pace could prove disastrous for the Yellowstone pines and countless other plant species.

Animals, too, are vulnerable to changes in climate. For instance, if plants are squeezed out of their ranges or into extinction, the animals that depend on them for food or shelter will be threatened. This could be the case with the Adelie penguins going hungry as their krill stocks dwindle (the marine plankton that the krill eat seem to be diminishing as sea ice melts). A University of California ecologist, Camille Parmesan, published an article last year in the journal Nature that is thought to be the first climate-related study to cover not just a local population, but the full range of a species. She found that warmer temperatures could be responsible for the 160-kilometer shift northward of a North American butterfly, the Edith's checkerspot.

Nature not only is affected by changes in climate; it also influences climate. The carbon dioxide that warms the atmosphere enhances photosynthesis, promoting plant growth. Plants take up carbon dioxide, so one might expect their heightened growth to curb global warming. This could be an example of a "negative feedback," in which one change sparks a counteractive response. Indeed, initial laboratory tests of increased carbon levels led scientists to foresee greener forests and more verdant fields. However, labs cannot replicate nature's complexity. Outside of the lab, warming contributes not only to plant growth but also to pest outbreaks that can kill the plants. When plants die, they can no longer take up carbon dioxide; instead they release it. While the future response of nature to ever greater levels of carbon dioxide cannot be predicted, the fact that concentrations of this gas are now at their highest in at least 160,000 years suggests that human carbon dioxide production has already exceeded nature's storage capacity.

Further complicating the picture are other large changes made to the planet by humans, such as the global excess of nitrogen from fossil fuels and industrial fertilizer. With the amount of industrial fertilizer used on crops during the 1980s alone exceeding all industrial fertilizer applied previously in human history, the amount of biologically active nitrogen on land has doubled from preindustrial levels. the double stress of too much carbon dioxide and too much nitrogen was observed in a 12-year field study of grasslands. In the short term, nitrogen spurred plant growth, and the plants took up more carbon dioxide. But in the long term, the added nitrogen caused a change in the species mix, favoring plants that are less adept at taking up carbon. One of the lead authors, David Wedin of the University of Toronto, concluded: "The ecosystems that do a good job of storing carbon are the very same ones we're losing because of the added nitrogen." the same sort of shift could also occur in forests, which play an even bigger role in carbon storage.

One-third of the world's forested area could undergo major changes with a doubling of carbon dioxide. Climate change could be a further stress on forests already under siege from acid rain and fragmented habitat. In the North, boreal forests are particularly vulnerable. Forest fires, a normal part of forest ecology, are likely to increase in frequency and severity, substantially decreasing forest cover and releasing additional carbon dioxide. Several studies predict a dramatic surge in Canadian forest fires that could increase by 40 to 50 percent the area burned each year. In Russia, an additional 7 to 12 million hectares are projected to burn annually within the next 50 years, affecting 30 to 50 percent of the land area. Scientists cited by the IPCC expect that during the next century, boreal forests will be diminished to such an extent that the supply of industrial roundwood will cease to meet demand.

The effects of climate change on nature promise to cascade into the global economy. A shifting climate threatens not only the goods that nature provides us, such as timber, food and genetic resources, but also such vital services as the cleaning of air and water and the pollinating of crops by insects (see Janet Abramovitz's article in the forthcoming January/February 1998 issue). Robert Costanza, a University, of Maryland economist, and colleagues recently estimated the cumulative value of these services to be in the neighborhood of $33 trillion per year, which compares to the Gross World Product of $28 trillion.

By continuing to load the atmosphere with greenhouse gases, we are putting many of these valuable services at risk. Canada's MacKenzie River Basin, for instance, depends heavily on water transport. Climate change is projected to lower the minimum water levels in the region's waterways, which would hinder navigation - an important natural service. Coastal wetlands also provide us with myriad services: habitat for lucrative fisheries, protection against storms, and improved water quality through sediment, nutrient, and pollution removal. While coastal development is already encroaching on wetlands, climate change brings the added risk of sea-level rise and the potential for more intense storms. Along with many other industries, tourism stands to lose in the face of such changes. Without coastal protection, attractive beaches will erode - a particularly dire prospect for many small island states, where tourism often accounts for more than a third of GDP.

Risking Our Food and Water

As farmers are well aware, the availability of fresh, salt-free water is a crucial service we obtain from nature. Farmers in the midwestern United States are not likely to forget the summer of 1988. Below normal rainfall and record-breaking temperatures combined to create a crop-withering drought. Grain yields dropped by 30 percent, causing production to fall below demand for the first time in U.S. history.

By itself, this single drought is not evidence of climate change. It is, however, a scenario that we may see more frequently in a warmer world - and it highlights the risks that climate change poses to our food and water supplies. On average, the interiors of large continents are expected to warm up and dry out, prompting increased demands for water. One study cited by the IPCC suggests that many mid-latitude locations, like the United States, would experience more droughts: the frequency of severe droughts that currently occur only 5 percent of the time could rise to 50 percent by 2050.

Water is already scarce in many areas. Humans now use more than half of the world's fresh water. Even without climate change, countries with high population growth rates are likely to suffer water shortages. Nations that are already water-limited, such as Kuwait, Jordan, Israel, Rwanda, and Somalia, are likely to face substantial costs. In the United States, the Environmental Protection Agency (EPA) predicts that the warming from a doubling of carbon dioxide would reduce by 7 to 16 percent the annual water supplies in California's Central Valley basin, where water demand is expected to rise by more than 50 percent as early as 2010.

The possibility of more droughts is a risk to food production, but in the absence of droughts, warmer temperatures may actually be a boon in some places. Decreased frequency of severe frosts may help to boost crop productivity. While some crops may benefit, climate change is likely to

sharpen agricultural inequities between the rich and poor. Wealthier countries may employ "technological fixes" to evade some climate hazards, but the developing world is far more vulnerable. A study commissioned by the US EPA found that climate change was expected to decrease global production of wheat, rice, and other grains 1.2 to 7.6 percent by 2060. Poor countries, the study estimated, would take the brunt of this shortfall. Industrial countries would see production decrease slightly, or perhaps even increase by as much as 11.3 percent. Developing countries, on the other hand, would see losses of 9.2 to 11 percent.

Even assuming reduced levels of population growth and full trade liberalization, climate change would likely increase the number of people in developing nations at risk of hunger. Depending on the assumptions, the population at risk would increase by 18 million to 412 million. At greatest risk for famine are those who rely on isolated agricultural systems in sub-Saharan Africa, South and Southeast Asia, tropical areas of Latin America, and some Pacific Island nations. But if climate change causes famine in one part of the world, then other countries will feel the pain too, as environmental refugees course across their borders. Nobel laureate and MIT physicist Henry Kendall believes industrial nations in particular ought to see this as a national security risk, warning U.S. President Bill Clinton: "it is not the case that one end of the boat can sink."

The productivity of lakes and oceans is also at risk. Fish thrive in nutrient-rich waters. Warming is expected to reduce the vertical mixing of lake water, impeding nutrient distribution. This would harm freshwater fisheries in lakes such as Africa's Lake Malawi, habitat of 500-1,000 fish species that are an important source of food to local people, and prey to local birds.

Oceanic fisheries, too, are temperature sensitive. Paleoclimate studies indicate that earlier warmer eras were marked by a decrease in global oceanic productivity. Worldwide, about 90 percent of commercial fish are caught within 200 nautical miles of the coast, many in coastal upwellings of cold water. Warmer temperatures could weaken the mechanisms that produce these upwellings. Off the coast of California, a warming of the sea surface by as much as 1.5 [degrees] C since 1951 has led to an 80 percent decline in zooplankton, which are vital to the oceanic food chain.

Warmer sea water, however, speeds up the metabolism of the more toxic species of algae. Algal blooms, often in the form of red or brown tides, can kill fish and sicken people who eat contaminated seafood. A recent surge in toxic algal blooms worldwide may be the result of new synergisms. Algal blooms thrive in warmth, as well as in nitrogen-rich waters, which are increasing thanks to human activities. As industrial fertilizer production and fossil fuel burning release more nitrogen, coastal wetlands and mangroves, which normally filter out nitrogen, are being lost to coastal development and aquaculture.

Coastal wetlands and other shoreline habitats, at tremendous risk from sea-level rise, sustain valuable fisheries: about 70 percent of the ocean's fish depend on near-shore areas at some point in their life cycle. As sea level rises, fish production could initially increase as marshes fragment, flood, die, and decompose, and nutrients become available from leaching of soils and flooded peat. But ultimately, the loss of nesting sites and refuge would likely damage fisheries.

Coral reefs, dubbed the "tropical rainforests of the sea" for their rich biological diversity, are another marine habitat at risk. Reefs are already suffering from overfishing, pollution, and enhanced sedimentation - stresses that may increase the corals' vulnerability to a blip in temperature. An increase of 1 to 2 [degrees] C can cause corals to "bleach," as they expel the algae that provide them with food and lend them their vibrant colors. Sustained increases of 3 to 4 [degrees] C can cause significant coral death. Warmer than normal sea water has contributed to extensive coral bleaching near the Galapagos Islands off the coast of Ecuador and elsewhere in the eastern Pacific, Caribbean, and adjacent Atlantic.

Threats to Health

When corals bleach, they offer a particularly vivid sign of a species under stress. Humans can provide another striking example. In July 1995, for instance, a heat wave paralyzed the city of Chicago for nearly a week. Sustained high temperatures directly contributed to the death of 500 people.

As we continue to add gases to the greenhouse stew, we may be increasing the risk of heat-related deaths. Even a small hike in average temperature can increase the risk of heat waves. The U.S. National Climatic Data Center has shown that a 3 [degrees] C increase in Chicago's average July temperature would increase the probability of the heat index (a measure of temperature and humidity) exceeding 49 [degrees] C during the month from one in 20 to one in 4. More very hot days translates into more deaths; studies analyzing heat waves tend to find a threshold temperature beyond which mortality rises rapidly. There may be fewer cold-related deaths as a result of climate change, but scientists expect increases in the number of heat-related deaths to outweigh this positive trend.

Heat waves can be especially deadly in cities, because hot weather accelerates the chemical reactions that produce urban smog, which can cause respiratory distress. Particularly vulnerable are city dwellers in the developing world, where pollution is worse and air conditioning less common.

Another health threat comes from infectious diseases, which may surge as temperatures rise. Such illnesses are already on the rise - emerging from forests cleared for human settlement, being spread by international travel, and mutating to resist existing remedies (see Anne Platt, "The Resurgence of Infectious Disease," July/August 1995). Climate change could amplify, the existing problem. Take malaria, which causes 1 to 2 million deaths annually. The Anopheles mosquito, as well as the malaria-causing parasite it carries, cannot survive in cool weather. But as the mercury rises, Anopheles shifts into high gear, feeding and reproducing more quickly. With the temperature increase scientists expect to see from a doubling of carbon dioxide, the proportion of the world's people living within malarial zones could jump from 45 percent today to 60 percent by the latter half of the next century. Rwanda has already felt this transition on a smaller scale: cases of malaria have more than doubled since the early 1960s, as average temperatures have climbed nearly 1 [degree] C. Among Rwandans living in high-altitude areas - cooler zones that previously had seen little or no malaria - the increase was more than fivefold. With further warming, large urban highland populations that are now malaria-free - including millions of people in cities such as Nairobi, Kenya and Harare, Zimbabwe - could be at risk.

Higher temperatures may also help spread dengue fever - called "breakbone fever" by those who know the intense pain it causes in joints. Like the malaria parasite, the dengue virus hitches its ride on a mosquito, usually Aedes aegypti, that thrives in warm conditions. A study sponsored by the Asian Development Bank foresees a four-fold increase in dengue fever cases in Indonesia as projected warming in the next century causes mosquitoes to move into cooler, mountainous areas. Already, since 1993, dengue has been found at higher elevations than ever before: at 2,200 meters in Colombia and 1,700 meters in Mexico. Meanwhile, a hardier dengue vector, the Asian tiger mosquito, has established itself in the Southeast United States, and has begun to extend its range northwards towards Chicago and Washington, DC.

Another scourge closely linked to climate is cholera, a water-borne illness that attacks the human small intestine. The cholera bacterium is thought to originate in South Asia, from which it is carried to Latin America on ships that discharge ballast water near the coast. In 1991, a cholera epidemic struck a 2,000-kilometer stretch of the Peruvian coast. Before the incident ended, 500,000 people fell ill and 5,000 died. A lone ship could have introduced the disease, and poor sanitation was to blame for infecting local populations, but other factors must have been at work to spread the bacterium so far. Scientists tied the outbreak to a climatic event, El Nino, which brings warm sea surface temperatures, heavy rains, and nutrients from the land to the west coast of South America, fostering plankton blooms that carry the cholera bacterium.

People who live near areas of endemic disease will be particularly at risk if the boundaries of tropical diseases are extended by warmer temperatures. As Paul Epstein of the Harvard School of Public Health points out, "rodents and insects carry no passports." Infectious diseases could easily migrate to northern, industrial countries, where natural immunity is low. Nonetheless, these countries are better equipped to suppress disease outbreaks. Hardest hit will be those in developing countries, where infectious disease is already a major cause of illness and death. George Alleyne, director of the Pan American Health Organization, suspects climate change "will be one other phenomenon that widens the health gap between groups of people."

Floods and Storms

If the planet's average temperature continues to climb, then more water will both evaporate and precipitate. The consequences of this greater cycling of water are still unclear. Some regions may see more intense rains of the kind that devastated Eastern Europe during the summer of 1997. Those rains caused floods that swallowed homes, crops, highways, and factories - and sent national economic advisers in Poland and the Czech Republic scurrying to revise their forecasts for economic growth. Weeks of severe flooding killed at least 100 people and caused billions of dollars worth of damage.

While moderate rains benefit agriculture and water supplies, heavy rains of the sort that drenched Eastern Europe in 1997 allow more water to run off into the sea and are more likely to trigger floods. Meteorologist Thomas Karl and his colleagues at the National Climatic Data Center have found evidence that there is actually a trend towards heavier rains in the United States. While total precipitation has increased by about 10 percent in the United States from 1901 to 1996, there has been little increase in the beneficial moderate rains. Rather, most of the increase has been in the extreme events, such as floods and storms. Karl believes that warmer temperatures may be responsible for the increase in the extremes.

As the atmosphere warms, changes in the intensity and frequency of hurricanes (also called tropical cyclones or typhoons) are likely to vary by region - with some areas deluged and others in drought. A study by Germany's Max Planck Institute suggests that the warmer ocean temperatures expected from a doubling of carbon dioxide will resemble semi-permanent El Nino conditions. El Nino appears every few years when trade winds that push surface ocean currents away from the west coast of Peru weaken or even reverse, allowing warm water to flow back towards South America, bringing heavy rains to the Eastern Pacific while stranding the Western Pacific in a drought. These events set in motion a chain of weather anomalies around the world. While the link between El Nino and climate change has yet to be proven, El Ninos have occurred more often since 1977, with an unusually prolonged event from 1990 to 1995. The century's strongest was in 1982-83, but that title is likely to be claimed by the one underway now, which began in late 1997. If climate change spurred a semi-permanent El Nino, there would be fewer Atlantic hurricanes in the United States, but more intense tropical cyclones in the Pacific, and more typhoons in Asia.

The effect of climate change on the overall frequency of storms is uncertain. Climate models are not good at replicating these weather extremes. However, the response of oceans to warmer temperatures leads some scientists to believe that storms, whatever their frequency, will be more intense. As the ocean is heated, water expands, raising the average sea level. This, of course, may be hastened by the melting of sea and mountain ice. Warmer sea surface temperatures feed storms, and higher sea levels intensify storm surges.

Today, 46 million people live in areas that are at risk of flooding due to storm surge. If a warmer climate causes the sea level to rise by 50 centimeters, the number of people at risk will double to 92 million - even without accounting for anticipated population growth. In Indonesia, for instance, urban populations are concentrated in low-lying coastal areas; of a total population of 180 million, 110 million live near the shore. Sea level rise is of particular concern in Jakarta, where parts of the city are already subsiding due to the exploitation of ground water.

There is also high risk of flood damage from sea-level rise along the Indian Ocean coast, the south Mediterranean coast, the African Atlantic, the Caribbean coasts, and many small islands. University of Maryland researchers have found that more than 94 million people are at risk from future sea-level rise of 1 meter in Egypt, Bangladesh, China, and Nigeria - mostly around river deltas. Many populated deltas are already affected by land subsidence or sediment starvation by upstream dams. In Bangladesh, the Sunder-bans - the largest mangrove forest in the world - would probably be destroyed (it is already threatened by salt intrusion because the flow of the Ganges has been diminished by diversion of water to cities). The U.S. Atlantic and Gulf coasts would also be imperiled; sea level in the Mississippi Delta is already rising faster than the average sea-level rise worldwide.

Regardless of changes in climate, storms will cause more damage as the result of another trend: more people living in coastal cities. Already, two-thirds of the world's population lives within 60 km of a coast, and this number is expected to rise to three-fourths by 2010.

An increase in flood and storm damages, whatever the cause, could bankrupt the insurance industry. Insured property values on the Gulf and Atlantic coasts of the United States alone totaled $2 trillion in 1988. The insurance industry is already suffering from a spate of "billion dollar" storms that have occurred since 1987. In the United States, there has been as much damage from hurricanes in the 1990s as the combined total of the 1970s and 1980s, even after adjusting for inflation. Insurance companies, well-versed in risk assessment, are increasingly concerned about the risks climate change might pose to their business. (See Christopher Flavin, "Storm Warnings," November/December 1994.)

Anticipating Surprises

Ultimately, the most serious results of climate change may be the hardest to predict. As ecologist Norman Myers explains, when climate change combines with pollution or another environmental problem: "the outcome may be not a double problem, but a super-problem." The climate system itself is full of such "non-linear" possibilities, because it is so complex. A tale from one of the earliest pioneers in chaos theory helps to explain this:

In 1961, as James Gleick, author of the book Chaos, tells it, MIT meteorologist Richard Lorenz was playing with his favorite new toy, an early computer model of the weather. When Lorenz entered data for initial weather conditions, his computer - big and clunky by today's standards - solved a batch of physics equations and then spewed out results for future winds, rain, and temperatures. One day, trying to redo part of an earlier run, Lorenz re-entered his data. As he examined the new printout, he expected it to look like the old one. He was surprised. The second time around he had used more rounded numbers (.506 instead of .506127). At first, the second run resembled the first, but then, over time, it began to diverge so sharply that no similarity could be seen.

Lorenz had stumbled into a new field of science now known as chaos. Climate, like Lorenz's model, is chaotic: small changes in important parameters can cause unexpected, non-linear, results. In the words of climate scientist Richard Somerville, "Just as a finger on a trigger can set off an explosion, so a very subtle change in a climate input can have a massive change in a climate output."

So as we push greenhouse gas concentrations to record levels, we are making an important change to one "input" in the Earth's climate system. A leading climatologist writing in the October 1946 Scientific Monthly expressed a dominant view of his time: "We can safely accept the past performance as an adequate guide for the future." But as we reach unprecedented levels of carbon emissions, the past may no longer be a good reference. Paleoclimatologist Jonathan Overpeck of the U.S. National Geophysical Data Center recently summed this up in the journal Science: "If the climate system turns out to be highly sensitive to elevated atmospheric trace gas concentrations, then we may be confronted with modes of climate variability without precedent."

What sort of surprises might the climate system have in store? The answer can be found in "positive feedbacks" - the potential for initial climate changes to spur even greater change. Warming, for instance, could cause changes that could in turn lead to the slowing or stopping of the North Atlantic oceanic "conveyor belt." This conveyor, with a flow equal to 100 Amazon Rivers, brings heat from the Gulf Stream to Europe. In the Norwegian Sea, heat from the sea is transferred to the air, so the water becomes saltier and denser and falls to the ocean floor, setting up a current that circulates around the world. Warmer temperatures in the high latitudes could slow the evaporation process; or mountain glaciers and polar ice could melt, infusing the Norwegian Sea with fresh water. In either case, the pool of northern water would not become as dense as it gets today, and the density differential that drives the conveyor would be lessened. Without this transport, fisheries could collapse, and Europe might be plunged into a mini-ice age. Winter temperatures in the North Atlantic could abruptly plummet: within 10 years, Dublin might have the climate of Spitsbergen, which is almost 1,000 kilometers north of the Arctic Circle. University of Bern climate modelers recently found that the rate of greenhouse gas emission is critical, because the strength of the conveyor depends on such subtle density differences. Wallace Broecker, an oceanographer at Columbia University who has extensively studied the conveyor, concludes: "Far from being self-stabilizing, the Earth's climate system is an ornery beast which overreacts even to small nudges."

This scenario points to a problem with our climate models. We have been asking them to tell us what might happen if carbon dioxide concentrations were doubled. But concentrations are not steady and will not necessarily stabilize at that level. It is not unimaginable that concentrations might eventually quadruple. And studies by climate modelers at the National Oceanic and Atmospheric Administration's Geophysical Fluid Dynamics Lab in Princeton, New Jersey indicate that the oceanic conveyor might indeed shut off entirely if that happens.

Furthermore, one climatic surprise may trigger cascading surprises. For instance, Princeton researchers have suggested that a weakened conveyor could undermine the oceans' capacity to remove carbon dioxide from the atmosphere. As ocean circulation slowed, the seas would absorb much less carbon dioxide, leaving more of the heat-trapping gas in the atmosphere to feed further warming. Or, if the ocean conveyor were to shut off completely, then the surface air temperature in the Northern Hemisphere could suddenly drop. Such a drop could limit the capacity of the boreal forests to take up carbon dioxide - again, resulting in additional buildup of carbon dioxide in the atmosphere.

Another surprise may come from the response of forests to warming. While forests play a key role in taking up carbon dioxide, some scientists predict a net release of carbon dioxide as rising temperatures change the optimal geographic range of trees. Recall the Yellowstone pines that could die at the southern end of their range and might not be able to quickly take root in cooler climes as the atmosphere warms. The death of such trees could release more carbon dioxide than could be taken up by new tree growth. In any case, much is still unknown about the role that plants play in stabilizing the climate, or about how changes in vegetation will subsequently affect the climate system. For instance, trees and plants tend to absorb more sunlight than does snow or tundra. Thus, forests that spread into formerly barren tundra as temperatures rise may end up absorbing more solar energy than the tundra does, thereby increasing the warming.

In all these cases, the climate may eventually swing back. Not only can complex systems go haywire as a result of positive feedbacks, but also they can be corrected by negative feedbacks. Take the human body, another complex system with countless feedback loops. When a healthy person gets too hot, sweating cools him down. An ill person, however, might sustain a high fever (and perhaps even die) despite the sweating and other such negative feedbacks. Human domination of the earth's ecosystems - from nitrogen overload to increased demand for water to deforestation - is thwarting natural negative feedbacks that could slow global warming. For instance, by cutting down forests that store carbon, we are weakening a negative feedback. Even if the warming is corrected by natural phenomena in the long run, the time scale that climate operates on is far longer than the lifespan of humans. By the time the Earth's "fever" breaks, it may be too late for us. Jerry Mahlman, director of the Princeton lab that has modeled the quadrupling of carbon dioxide, explained to New York Times science writer William Stevens: "If you get to where you don't like it, there's not a lot you can do about it - you're wired in for a long time."

Minimizing the Risks

The point that Mahlman stresses - that a shift to an inhospitable climate could be irreversible on a human time scale - is important. It means that climate change could be a catastrophe from which humans never recover. The nations of the world, in signing the 1992 climate change treaty, acknowledged that the devastating prospects identified by scientists are unacceptable risks. However, in the five years since that agreement, emissions of greenhouse gases have continued to rise, and there is still no plan in place to hedge against climate catastrophe. When delegates gather in Kyoto this December, they will have a clear choice: to expose the world to further risk by gambling on the status quo or to produce a strategy to minimize the risks.

How might the delegates proceed? One proven way to minimize risk is to assemble a diverse "portfolio" of options. This approach was validated in 1952, when a young University of Chicago graduate student showed mathematically that it is risky to put all one's eggs into one basket. Wall Street players quickly canonized his findings: if one stock should fail, a diverse portfolio of investments protects against financial ruin. So too could a diverse portfolio of technologies and policies hedge against the risks of climate change. Just as an investment portfolio contains different types of assets (such as stocks, bonds and mutual funds) a climate portfolio would include three types of actions: further study of the climate system, preparations to respond and adapt to climate changes, and - most urgently - a reduction in the rate at which greenhouse gases build up in the atmosphere.

Sustained scientific research, the first item in the portfolio, is essential for several reasons. Although the goal of the climate treaty is to avoid "dangerous" concentrations of greenhouse gases, exact threshold levels cannot be predicted with certainty. As scientists get a better idea of how the climate system's many feedback loops operate, they may be able to better gauge the rate and magnitude of projected changes (currently, the estimated range of outcomes is quite large, to account for scientific uncertainty). Important avenues of investigation include, among others, the role that clouds play in both trapping and reflecting solar energy, the various ways in which ecosystems are linked to climate, and the interaction between oceans and atmosphere.

Scientific research is also crucial because it helps inform the second part of the portfolio: strategies to adapt to climate change. A key, long-term goal of climate change research is accurate projections of how certain regions will be affected. Such information would allow governments to more cost-effectively implement strategies to adapt to sea-level rise, localized drought, heat waves, and other adverse effects. Water supplies might be better managed, for instance, or farmers might be able to shift to more resilient crops. Development could be restricted in floodplains and wilderness corridors could be created to allow for plant and animal migration. Adaptation measures are important, but the dividends we can expect from this part of the portfolio are necessarily limited. Many effects of climate change would be difficult, if not impossible, to manage: the inundation of coastal zones and small island states, the eradication of species, or a shut-off of the ocean's circulation.

The Risks of Climate Change

Natural and man-made systems alike rely on certain climate
parameters. This is just a thumbnail sketch of what's at stake
when we gamble with the climate:

AREA                       SELECTED RISKS

Ecological Systems

Forests                    Major vegetation changes in one-third of
                           global forests; disappearance of entire
                           forest types; more frequent and intense
                           forest fires.

Terrestrial &
aquatic ecosystems         Extinction of certain plants and animals
                           as their range shifts.

Deserts                    Hotter but not welter conditions in some
                           areas. Increased desertification.

Mountains                  Extinction of mountain-top plants and
                           animals; loss of one-third to one-half of
                           global glacier mass over the next
                           century.

Oceans & coastal systems   Inundation of coastal wetlands, coral
                           reefs, and river deltas.

Socioeconomic Systems

Water resources            Large decrease in per capita water
                           availability in some areas.

Agriculture                Hunger and famine in areas dependent on
                           isolated agricultural systems (i.e. in
                           sub-Saharan Africa, parts of Asia,
                           tropical areas of Latin America)

Fisheries                  National and local fisheries vulnerable
                           to shift in species mix and production
                           centers. Subsistence and small-scale
                           fishers disproportionately at risk.

Insurance industry         Difficulty in adjusting premiums, due to
                           unpredictable changes in extreme weather
                           events. Bankruptcy of industry from more
                           frequent or larger disasters.

Human Health

Habitat                    Large coastal cities particularly at
                           risk. Damage from coastal storm surges,
                           floods, landslides, windstorms, rapid
                           snowmelt, tropical cyclones, and forest
                           or brush fires.

Disease                    More heat-related illness and death.
                           Greater transmission of vector-borne
                           diseases as range and seasons of vectors
                           increase.

Source: IPCC, Climate Change 1995: Impacts, Adaptations and
Mitigation of Climate Change.

Thus, the centerpiece of the portfolio is slowing the greenhouse gas buildup in the atmosphere. This is the one clement that squarely addresses the cause of climate change. Of course, to slow the accretion of greenhouse gases released around the world, national governments will have to cooperate. On the table at Kyoto will be a proposal from the European Union that industrial countries reduce their emissions 15 percent from 1990 levels by 2010. Other countries, including Australia, the United States, and Japan, are likely to push for less stringent targets. A requirement to begin slowing emissions now, instead of later, will expose us to considerably less risk. Continued acceleration of emissions now speeds the rate of climate change, which could cause temperatures to reach important ecological thresholds sooner.

Fortunately, there are many cost-effective actions that can be taken to reduce emissions. Fossil fuel combustion is the single largest source of carbon dioxide emissions, so a diversification of the world's energy infrastructure could offer the greatest long-term protection. Countries and private investors need not tic their futures to the fuels and technologies that have led the world to the brink of climate disruption. In the 1990s, there are an array of cost-effective alternatives. Energy producers can switch to clean and economical energy sources such as wind and sunlight. And the amount of energy consumed could be greatly reduced by the use of more efficient technologies. Indeed, this is the investment advice espoused by London's Delphi Group, which advises large institutions on investment policies. "Avoid maintaining long term overweight positions in the 'carbon fuel' industry," the group's 1995 report cautioned banks and insurance companies, explaining: "the alternative energy industry offers greater growth prospect than the carbon fuel industry."

New wind turbines, for example, produce emissions-free electricity at a generating cost comparable to that of new coal-fired plants. And the cost continues to fall as the industry expands at a rate of 25 percent per year. The solar power industry is also growing at double-digit rates. Already, solar is the least-cost electricity option for many rural areas; an estimated 400,000 homes far from electricity grids are using solar panels. Also on the market are options to improve the energy efficiency of buildings and vehicles. These include more efficient lights and appliances, small gas turbines that generate both power and heat, and a new generation of lightweight hybrid electric cars. Until now, government policies have hindered such technologies. By removing fossil fuel subsidies and introducing market incentives for the new technologies, governments could help turn this situation around. Of course, to be effective, such technological advances will have to be combined with a stabilization of the human population worldwide.

As climate change negotiations have progressed, coal and oil interests have shown a parochial interest in keeping the world's energy system dependent on them - witness the multimillion dollar, pre-Kyoto media blitz. Certainly, the fossil fuel industry stands to be diminished. But companies can still survive, and even flourish - if they diversify. As opportunities fade in fossil fuels, new ones will open in renewable energy and energy efficiency. There are a host of win-win solutions. An analogous scenario began to play out ten years ago, when nations agreed to the 1987 Montreal Protocol, which curtailed global use of the chlorofluorocarbons (CFCs) and other compounds that destroy the ozone layer. Companies such as Dupont that produced CFCs ended up profiting from the production of ozone-friendly alternatives. And many companies that had been using CFCs developed more efficient, CFC-free production processes that ultimately saved them money.

Still, the fossil fuel lobby continues to deflect attention from the risks of climate change by asserting that the risks to the economy are a greater public concern. But the economic models they use do not allow for policy and technology changes that will make fossil fuel alternatives much less expensive than they are today. Nor do they account for the fact that a cleaner, more efficient energy economy would yield tremendous benefits that are not even related to climate change. For instance, a departure from fossil fuels could significantly lower energy costs. In 1997, a study by a group of energy and environmental organizations found that U.S. carbon emissions could be cut to 10 percent below the 1990 level in 2010 while reducing national energy costs by $530 per household and creating nearly 800,000 jobs annually. Similar research in Canada, Japan, Europe and Australia has found that reductions in carbon dioxide emissions could enhance the economy. Other benefits, not even accounted for in these studies, include less local air pollution and regional acid rain, fewer tanker accidents and strip mines, decreased trade imbalances, and increased national security. This means we would receive dividends from our climate portfolio - even if the catastrophe never occurs.

Along with energy reforms, better forest management could slow carbon dioxide accumulation. Trees take up carbon dioxide from the atmosphere and release it when they decay. Deforestation accounts for as much as a third of the carbon dioxide added to the atmosphere from human activities. But if we halt deforestation and actually increase forest cover - through better conservation, management, and reforestation - then forests may be able to slow the buildup of atmospheric carbon dioxide.

Release of other greenhouse gases, too, could be cut. For instance, many low-cost options exist to reduce methane emissions from industrial sources. The U.S. EPA has found that up to 90 percent of the methane released from landfills can be profitably eliminated, providing side-benefits such as improved air and water quality near dumpsites and less risk of fires and explosions. Another step would be to curb the release of halogenated compounds, primarily perfluorocarbons (PFCs) and hydrofluorocarbons (HFCs), highly potent and long-lived greenhouse gases that are on the rise, as they are increasingly substituted for restricted ozone-depleting chemicals.

In hedging against climate change, the Kyoto protocol can guard against a wide range of seemingly unrelated problems. Alteration of the global carbon cycle is just one of the large changes humans have been making to the planet. Others - increasing our population, cutting down forests, using more water, and releasing more toxins - also have profoundly detrimental consequences, which stand to be worsened by climate disruption. By beginning to reduce the risks of climate change, we will be narrowing our risk of exposure in other areas too.

December's climate treaty negotiations will take place in a city that has historically taken a dim view of gambling. A half-century after Pascal and Fermat first considered the gambling tables of Paris, other gamblers - Japan's notorious yakuza - tried to surface in Kyoto, but were quickly pushed underground. Diplomats arriving in Kyoto for the climate negotiations should be forewarned. Without quick action to reduce greenhouse emissions, they will be gambling with the planet. And they will have to answer not to Kyoto's local police but to the world, present and future.

Molly O'Meara is a staff researcher at the Worldwatch Institute.