Global warming is having a measurable effect on Earth's climate, including agriculture, freshwater resources, and plants and animals on both sea and land. These changes are expected to intensify as temperatures continue to rise.
Those are among the conclusions of a new report from the Intergovernmental Panel on Climate Change (IPCC), a UN-sponsored group of scientists. A summary of their findings released April 6 outlines climate changes and how researchers expect them to play out as warming continues. Their impact on society, the IPCC report says, will vary depending on the amount of actual temperature increase that occurs and humanity's capacity or ability to adapt to the changes.
"Not all of these effects are negative," notes Sharon Hayes, an official with the White House Office of Science and Technology Policy, who headed the US delegation to the week-long meeting in Brussels where scientists and political delegations hammered out the summary's final wording. At least during the early part of the century, for example, crop yields in wetter parts of the mid- and high latitudes, including regions of Russia, Canada, and the US, are expected to rise.
But the report also makes clear that as temperatures rise, negative effects increase, Dr. Hayes adds. And the poorest countries, which contribute the least to global warming, are expected to face the biggest challenges in coping with it.
The report unleashed an immediate chorus of calls for the US to adopt a climate policy that includes mandatory controls on green-house gas emissions. John Connaughton, who heads White House Council on Environmental Quality, told reporters during a briefing April 6 that the Bush administration is pushing two programs that will accomplish the same end: a commitment to higher auto mileage standards and to replacing 20 percent of gasoline consumption with biofuels in the next decade.
But for many observers, that's not enough. Noting that the IPCC report comes on the heels of this week's US Supreme Court ruling that the Environmental Protection Agency has the authority to regulate carbon dioxide as a pollutant, Eileen Claussen, president of the Pew Center on Global Climate Change, said in a statement, "We need a mandatory climate policy in the United States" – one that, among other things, would directly control CO2 emissions.
A broad range of ways to adapt are available, the IPCC report says. But too little is being done to prepare for the disruptive effects a warmer world is expected produce. Most of the attention so far has focused on efforts to curtail emissions of heat-trapping greenhouse gases, especially carbon dioxide, produced by human activity, such as emissions from coal-fired power plants. But the report notes that more emphasis must be placed on adaptation as well.
Efforts to encourage sustainable development can help countries improve their resilience. But the report notes that over the next 50 years, the regional effects of global warming could undermine efforts to achieve those development goals.
Scientists have outlined a range of effects that have already taken place; they vary depending on how regional climates respond to rising global average temperatures. But as scientists look ahead, broad patterns emerge. Among them:
Fresh-water resources. By the middle of the century, average river runoff is expected to increase by 10 to 40 percent in areas nearest the two poles and in some wet tropical areas. But it's expected to shrink by 10 to 30 percent in dry, mid-latitude regions as well as in dry tropical parts of the globe. Drought-prone regions are likely to expand their boundaries, while heavy snowfall and rainfall elsewhere raises the likelihood of more frequent and severe flooding.
Ecosystems. The report notes that if temperatures increase between 1.5 and 2.5 degrees C (2.7 to 4.5 degrees F.), 20 to 30 percent of the plant and animal species researchers have examined so far could become extinct.
Farming. Globally, food production overall improves if temperature increases locally remain with a 1 degree to 3 degree C range. Productivity is projected to fall if temperatures rise above that range.
Coastal areas. By 2080, millions of people are expected to be affected by floods because of sea-level rise, especially in regions with high land subsidence, such as the Louisiana coast, or regions in Asia and Africa with large, low-lying, heavily populated river deltas. Small islands, the report notes, are particularly vulnerable.
Human habitation. Cities and industries that sit along coastal areas or river flood plains are expected to face the largest challenges – especially in already poor countries. Even in wealthy nations the poorest people are likely to suffer most.
Public Health. The report sets out a mixed picture, with the heaviest effects falling on poor areas where health care services, sanitation, and sources of clean water already are scarce.
Researchers acknowledge that pegging the changes they see in specific physical and biological systems to global warming is difficult. Changes are being measured at a relatively small number of sites around the world. And they cover a relatively small number of ecological and physical systems.
Still, the report notes that out of 29,000 data sets contained in 75 studies regarding changes under way, 89 percent are consistent with what models project should happen as the world warms. And the warming patterns people are seeing regionally are consistent with broad distribution of temperature changes global-scale models.
Moreover, research over the past six year has allowed scientists to project the possible effects of warming more accurately based on each degree of temperature increase.