Turning up the heat: new warnings from scientists say the effects of climate change could be drastic if nations don't act quickly.

• Author: Smith, Patricia
• Position: ENVIRONMENT

We're running out of time.

That's the conclusion of a stark new report on climate change by the world's largest scientific organization. If the world doesn't address the issue of Earth's warming temperatures soon, the report says, the result could be severe food shortages as crops become harder to grow, rising sea levels that make many major coastal cities unlivable, and a large-scale extinction of plants and animals.

The report, by the American Association for the Advancement of Science (A.A.A.S.), which represents 125,000 scientists worldwide, warns that the effects of human-caused emissions of greenhouse gases are already being felt and that the window to do something about it is closing.

"The evidence is overwhelming: Levels of greenhouse gases in the atmosphere are rising," says the A.A.A.S report. "Temperatures are going up. Springs are arriving earlier. Ice sheets are melting. Sea level is rising. The patterns of rainfall and drought are changing. Heat waves are getting worse, as is extreme precipitation."

Greenhouse Effect

Despite warnings from scientists that the problem is urgent, a growing number of Americans don't believe climate change is real--23 percent, according to a recent survey by Weather.com. That's up from 16 percent a year ago.

Richard Lindzen, a professor of atmospheric physics at the Massachusetts Institute of Technology, is one of the few scientists who share their skepticism.

"A hundred years from now, I don't really know, but I don't think [the climate] will be radically different," he says. "The climate is always changing. It's natural variability."

The A.A.A.S. report emphasizes that an overwhelming majority of climate experts have come to a consensus: "Based on well-established evidence, about 97 percent of climate scientists have concluded that human-caused climate change is happening." The report makes clear, however, that the consequences it outlines are distinct possibilities, not certainties.

A new round of climate change warnings has also come from the Intergovernmental Panel on Climate Change (I.P.C.C.), the United Nations panel of experts. Their latest report says that another 15 years of failure to limit carbon emissions could make the problem virtually impossible to solve with current technologies. It predicts that climate change will slow down economic growth and possibly lead to violent conflicts over resources, large! scale migrations, and more people being displaced.

"Nobody on this planet is going to be untouched by the impacts of climate change," Rajendra Kumar Pachauri, I.P.C.C.'s chairman, said last month.

What is climate change? Scientists say the burning of fossil fuels like oil and coal--by everything from cars to power plants--has caused a buildup of carbon dioxide and other gases that trap heat in the atmosphere. There are other sources too: Cows, for example, emit methane gas.

These invisible gases let sunlight through, but they prevent some of the resulting heat from radiating back out to space.

Because they behave like the panes in a greenhouse, they're called greenhouse gases and their influence on Earth's temperature is called the greenhouse effect. The higher the concentration of greenhouse gases, the warmer the planet gets.

The level of carbon dioxide, the main greenhouse gas, is up 41 percent since the Industrial Revolution in the early 19th century. If present trends continue, it could double in a few decades. Already, the planet has warmed 1.4 degrees Fahrenheit since the 1800s.

Severe Weather

That may not sound like much, but many scientists see...