The impacts of climate change are diverse and could be damaging to billions of people across the world, particularly those in developing countries who are the most vulnerable. Many of the effects of climate change will have negative economic consequences. The number of severe weather events, for example, is likely to increase and intensify as a result of climate change, which could result in billions of dollars in economic damage annually (7) (see “Getting Down to Business,”).

The following is an overview of the potential implications of climate change.

Intensified and More Frequent Weather Events

The number of extreme weather events, such as heat waves, precipitation, floods, droughts, hurricanes, avalanches, and windstorms is expected both to increase and intensify because of climate change. (8)

Recent events demonstrate the consequences of extreme weather. In 2003, an abnormal and extreme heat wave in Europe killed more than 35,000 people. In 2005, at least 1,300 people died as a result of Hurricane Katrina, which hit the U.S. Gulf Coast causing an estimated $135 billion in economic damage. (9) New evidence shows that the recent increase in hurricane intensity is due to climate change, and figure 3 depicts the rise in category 4 and 5 hurricanes around the world since 1975. A study published in 2005 in the journal Nature links hurricane intensity and duration to the recent ocean-warming trends associated with climate change. This study also found that over the past three decades, the destructive power of hurricanes in the Atlantic and Pacific has doubled. (10)

Although no one particular heat wave, hurricane, or other extreme weather event can be attributed directly to climate change, it will likely cause these extreme weather events to intensify and occur more frequently over time.

Rising Sea Levels

Sea levels around the world are rising faster because of the melting of land-based ice and the thermal expansion of oceans. According to the Arctic Climate Impact Assessment (ACIA, an intergovernmental forum composed of the eight arctic nations), (11) in the past two decades the global sea level has risen by an average of 8 centimeters (3 inches), and projections show an additional rise of 10 to 90 centimeters (4 inches to 3 feet) during the twenty-first century. (12) This rise in sea level, coupled with heavier than usual precipitation, may increase the risk of flooding for tens of millions of people in coastal areas across the world. (13)

Of particular concern is the Greenland Ice Sheet, which has been melting since 1979 more quickly than expected. Models indicate that over the longer term, climate change may eventually lead to its melting completely, which would raise the sea level by about 7 meters (23 feet). (14)

Water Shortages and Threats to Food Security

Water scarcity currently affects 1 billion to 2 billion people worldwide. (15) Climate change may exacerbate this serious problem, as prolonged droughts and spreading desertification could stress already scarce water resources. (16) Regions that rely on glacial melt water for their dry season water supply, such as the Himalaya-Hindu Kush region which includes China, India and other parts of Asia and is home to fifty to sixty percent of the world’s population, may be impacted as glaciers recede and dry season water sources are not replenished. (17) In addition, climate change may threaten global food security, as agricultural productivity in the tropics and subtropics is projected to slow because of excessive heat and droughts. (18)

Disease and Other Health Effects

Climate change could expand the geographic distribution of and exposure to infectious diseases like malaria, dengue fever, cholera, and Lyme disease in parts of Africa, Asia, Latin America, and North America as warmer weather allows these and other diseases to thrive in locations previously too cold to support them. (19)

The World Health Organization estimates that climate change caused more than 150,000 fatalities in 2000, a figure projected to increase in the future. (20) Diseases linked to climate change that are attributed to fatalities and illnesses are cardiovascular mortality and respiratory illnesses due to heat waves, altered transmission of infectious diseases, and malnutrition from crop failures. (21)

Disruption of the Ecosystem

Climate change could magnify the cumulative impacts of other ecosystem stresses caused by human development, such as air and water pollution and habitat destruction. Natural systems, including glaciers, coral reefs, atolls, mangroves, boreal and tropical forests, polar and alpine ecosystems, prairie wetlands, and remnant native grasslands, are particularly vulnerable and may be damaged irreversibly. (22) Considerable harm has already been done. For instance, according to the Millennium Ecosystem Assessment, in the last several decades of the twentieth century, about 20 percent of the world’s coral reefs were lost, and an additional 20 percent were degraded. This report also states that “by the end of the century, climate change and its impacts may be the dominant driver of biodiversity loss and changes in ecosystem services globally.” (23) Changes in ocean water temperature and salinity as well as in CO2 concentrations in ocean waters may compound other stresses placed on the world’s fi sheries, which would particularly hurt the poor. One billion people, mostly in developing countries, depend on fi sh for their primary source of protein. (24)

Habitat Destruction and Species Extinction

Habitat loss and ecosystem changes are expected to bring about a decline in the local diversity of native species by 2050, and the rate of extinction for these species may be hastened by climate change. (25) In the Arctic, warmer temperatures and melting sea ice caused by climate change will be particularly harmful to native species like polar bears and ice-dependent seals. It is unlikely that these species will survive the century if climate change persists. (26)