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close this bookClimate Protection and the National Interest (WRI, 1997, 56 pages)
close this folder2. THE CLIMATE CHANGE PROBLEM
View the document(introduction...)
View the documentThe Cooling Effect of Air Pollution
View the documentSearching for the Signal of Global Warming
View the documentExpected Impacts of Global Warming
View the documentCoping with Climate Change

Expected Impacts of Global Warming

Because CO2 and other greenhouse gases are so long-lived in the atmosphere, enhanced greenhouse warming can be expected to persist for centuries. The impacts - many of which are effectively irreversible25 - will affect everyone on earth. Human health, patterns and intensity of precipitation, water and food supplies, coastal development, energy supplies, the viability of natural systems: all will be affected if Earth's climate continues to change.

Several kinds of health impacts from higher temperatures have been identified, both direct and indirect. The long term will see the predominance of indirect effects, including the spread of vector-borne infectious diseases.26 Several such diseases, including malaria, dengue, and viral encephalitides, are particularly sensitive to changes in climate. The symptoms of dengue, a disease spread by mosquitos, include fever, pain. Its severe form causes widespread hemorrhaging. The disease is spreading north through Mexico and has been recently detected in Texas. In the past 20 years there has been a dramatic increase in dengue and dengue hemorrhagic fever worldwide with 50 to 100 million cases of dengue a year, and several hundred thousand cases in its severe hemorrhagic form. Two species of mosquito capable of spreading the disease have already entered the United States and fanned out across the lower Southeast.

The 1993 outbreak in the Southwestern United States of hantavirus pulmonary syndrome, a sudden respiratory disease, killed 53 percent of the people it struck. It provides a dramatic example of how a subtle climate change, even a temporary one, can promote disease27. The outbreak was traced to a 10-fold increase in the population of deer mice that carry the virus. This increase resulted from six years of drought (which reduced the population of mouse predators) followed by heavy rains in the spring of 1993 (and an abundance of food for the mice). The mice shed the virus in their urine, and contaminated dust spread the disease widely

The 1993 outbreak of hantavirus pulmonary syndrome - a sudden respiratory disease that killed 53 percent of the people it struck - provides a dramatic example of how a subtle climate change, even a temporary one, can promote disease.

More directly, the frequency of heat-related illness and death is expected to increase. Extreme heat waves can bring on heart attacks, strokes, or other fatal ailments in people at risk. Using models that estimate climate change for the year 2020 and 2050, researchers estimate that summer mortality will increase dramatically and winter mortality will decrease slightly.28 (Researchers estimate that perhaps 40 percent of those dying from heat waves would have died soon regardless of the weather.) Other direct health effects include deaths and injury from more extreme weather events (floods, storms, winds).29 Additional warming in urban areas would accelerate the formation of air pollutants such as smog (largely ozone), with negative consequences for human health. In sum, a sizable net increase in weather-related human mortality is expected if the climate warms as the models predict.30

Changing precipitation patterns can also lead to major social upheaval. The disastrous 1996 - 97 winter and spring floods in various regions of the United States illustrate what could lie ahead. The National Oceanic and Atmospheric Administration (NOAA) expects extreme flooding like the December 1996-January 1997 floods in the Northwest to become more frequent across the country due to an increase in precipitation extremes caused by climate change.31 These storms led to 30 deaths, to the evacuation of more than half a million people, and to property losses exceeding several billion dollars (including $1.8 billion in California, $500 million in Nevada, and $125 million of insured losses in Washington state).

A continued warming of the earth will lead to other impacts. Sea-level rise will threaten cities and countries worldwide. The IPCC's best estimate of sea level rise from 1990 to 2100 is about 49 cm (19 inches).32 Ocean levels would continue to rise long after the year 2100, however, until the oceans reach thermal equilibrium. Continued sea-level rise would erode barrier islands and virtually eliminate some island chains, such as the island nation of Maldives in the Indian Ocean. Higher seas would inundate the productive coastal wetlands and estuaries upon which marine fisheries and wildlife resources depend; drive millions of people around the world from their homes; cause saltwater intrusion into coastal groundwater supplies; adversely affect nearby infrastructure such as highways, power plants, sewage treatment plants, beaches, and cultural and historical sites; and increase the severity of storm damage to lagoons, estuaries, and coral reefs.

Highly productive agricultural areas such as the deltas of the Nile, Ganges, Yangtze, and Mekong rivers would be seriously affected by sea-level rise, forcing millions of people to move inland. Continued warming would also lead to shifts in rainfall patterns as global precipitation increases, leading to changes in availability of water for irrigation, hydropower, and navigation. Unable to migrate fast enough to keep up with the changing climate, whole ecosystems would be lost.

Scientists expect impacts on agriculture to be mixed. Their models suggest that if carbon dioxide levels double, agricultural production could be maintained at projected baseline rates, though regional effects would vary widely.33 Still, uncertainties are great and many factors have not been examined for their impacts. The IPCC cautions that the model calculations supporting its conclusions take into account the fertilization effects of CO2 but "do not include changes in insects, weeds, and diseases; direct effects of climate change on livestock; changes in soil and soil-management practices; and changes in water supply caused by alterations in river flows and irrigation." Failure to integrate many key factors into climate models limits the ability of researchers to consider scenarios in which the climate is still changing and to fully address the costs and potential of adaptation.34

Because tropical storms such as hurricanes derive their energy from the oceans, it is possible that as the seas warm, there could be an increase in the number and intensity of such storms. A recent statistical analysis by scientists at the University College London concludes that the record warming of the Atlantic Ocean may have been the primary cause of the exceptional 1995 hurricane season which saw twice the usual number of hurricanes.35 While the years 1995 and 1996 were the two busiest consecutive hurricane seasons on record, and 1997 is also predicted to be above average (six hurricanes are predicted of which two are expected to be intense),36 a three-year period is too short to establish a trend. A natural cycle of increased hurricane activity similar to what occurred in the 1940-1960 period may be starting.


If the number of powerful hurricanes - of natural origin or the result of global warming - does increase, damages could be severe, the result of more people living in more expensive homes in vulnerable coastal regions. It is estimated that a class-5 hurricane striking the northeast United States coastal corridor from Delaware to Connecticut could cause over $50 billion in insured losses (perhaps twice that amount in total losses).37 The prognosis, according to the National Center for Atmospheric Research, is for an increased likelihood of such major storms: "it is only a matter of time before the nation experiences a $50 billion or greater storm, with multi billion-dollar losses becoming increasingly frequent. Climate fluctuations which return the Atlantic basin to a period of more frequent storms will enhance the chances that this time occurs sooner, rather than later."38 The possibility of devastating property losses has spurred the insurance industry to a growing interest in climate change and in options to reduce their vulnerability to these potentially financially disastrous storms.