What's Known

A majority of scientists agree that global warming does exist, but questions remain: How will it affect Earth and how dramatic will the changes be? Here's what's known:

• According to the Environmental Protection Agency, global warming is caused by the build up of carbon dioxide and methane in the atmosphere. CO2, useful in trapping heat to keep Earth warm, also causes temperature fluctuations that can alter the world's climate.
• The causes are undeniably human-- cars, electricity, heat and industry.