Where the presidential candidates stand on the environment

AT ISSUE: What should the U.S. government do about global warming?

The Earth's climate is changing. Parts of it are warming up. Other areas are becoming colder. And many storms are more dangerous. Most scientists agree that human activity is the main cause. Fossil fuels, such as gas that we use in cars and oil we burn at home, give off carbon dioxide (called carbon emissions) and other gases, which trap heat in our atmosphere. Nobody knows for sure what will happen if the planet continues to heat up. But scientists have seen enough changes in the environment, such as shrinking butterfly populations and melting glaciers, that many countries are taking action to help reverse the damage. Both presidential candidates say the United States needs to be a leader on this issue. Here's a look at what each one says he would do.

The issue in their own words

Sen. Barack Obama: "Global warming is not a someday problem, it is now. ... It's not the future any of us want for our children. And if we act now, and we act boldly, it doesn't have to be."

Sen. John McCain: "I want to assure you I will make this planet clean. ... We will hand to you a cleaner planet than the one you were living in before I became president of the United States."

By how much would each candidate cut carbon emissions? (Scientists recommend cutting them to 80 percent below 1990 levels by 2050.)

Obama: Supports reducing carbon emissions to 1990 levels by 2020 and to 80 percent below 1990 levels by 2050.

McCain: Supports reducing carbon emissions to 1990 levels by 2020 and to 60 percent below 1990 levels in 2050.

Where do they stand on pollution "permits," which companies would have to buy if their pollutants were more than the government allowed? (Low-polluting companies could sell permits to higher-polluting ones.)

Obama: Supports. Would auction pollution permits to businesses and use the money to help clean up the environment.

McCain: Supports. Would initially give away permits to some business but would move toward an auction. Hasn't said what he would do with the money raised.

How did each vote in the Senate on environmental issues?

Obama: In 2007, he missed votes on four major environmental bills before Congress.

McCain: In 2007, the Sierra Club said he was the only member of Congress who did not vote on any of the 15 major pieces of environmental legislation.