Whether it's the melting of the frozen glaciers that shroud Kilimanjaro, Africa's highest mountain, or the overall rise in the level of the oceans, global warming is reshaping the planet. While some people see global warming as a natural event, most scientists agree that fossil fuels, such as oil and coal, drive the temperature increase. When burned, fossil fuels release greenhouse gases, including carbon dioxide, into the atmosphere. These greenhouse gases trap radiation from the sun close to the surface of the planet, causing the planet to warm.
To stem the release of greenhouse gas, people around the world are using biofuels, such as ethanol or biodiesel, to power their homes, cars and factories. Some experts say that ethanol reduces greenhouse gas emissions up to 65 percent [source: Nebraska Ethanol Board]. Scientists in Australia say biodiesel made from cooking oil reduces greenhouse gas emissions by 87 percent compared with petroleum diesel [source: Science Daily]. Still, many people believe that growing and turning some energy crops -- especially corn -- into fuel, uses a huge amount of fossil fuel, contributing to the release of heat-trapping gases [source: Tillman and Hill].