Senators John McCain and Barack Obama agree that the U.S. government should play an important role in protecting the environment. To the candidates, that means having the United States lead international efforts to slow global warming by reducing harmful greenhouse gases, such as carbon dioxide, which trap heat close to the earth. It also means encouraging Americans to consider cleaner energy sources. There are several questions the candidates will face during the campaign:

• How much should the government be allowed to regulate industries that emit greenhouse gases?
• What alternative energy sources would be best for the nation in the long run?
• How can the U.S. make sure that its endangered and at-risk species are protected from climate change in coming years?

John McCain says America was right in not joining the Kyoto Protocol, an international treaty signed by most of the world's countries that calls for them to limit greenhouse emissions. But he still believes that the United States -- under its own terms -- should form international alliances that include developing nations, to combat global warming. Here are some of his plans:

• Propose the use of alternative energy sources, including nuclear power.
• Reduce the nation's dependence on foreign suppliers of energy, such as oil.
• Support a mandatory system to reduce carbon emissions by limiting the amount of greenhouse gases industries can emit.

Barack Obama says that America, being one of the largest producers of greenhouse gases, has a responsibility to lead in the global effort to reduce emissions. And clean-up should begin at home. Like Clinton, he promises to put in place a mandatory system that would reduce carbon emissions by limiting the amount of greenhouse gases emitted by industries. Here are some of his other plans:

• Create a government program that would share climate-friendly technologies with developing nations.
• Have rewards programs for forest owners, farmers and ranchers when they plant trees or use farming practices that capture carbon dioxide from the atmosphere.
• Give incentives to automakers to develop technology that produces more fuel-efficient vehicles.