According to the Natural Resources Defense Council, global warming is caused by “carbon dioxide and other air pollution that is collecting in the atmosphere like a thickening blanket, trapping the sun's heat and causing the planet to warm up.”

The United States is the largest source of CO2 emissions. We make up just 4 percent of the world's population, but we produce 25 percent of the carbon dioxide pollution from fossil-fuel burning -- by far the largest share of any country.

If we don't start curbing greenhouse gas emissions now, there is a significant risk that global warming will raise the sea level by 1-3 meters in this century.

Poor countries depend mostly on agriculture and tend to be located closer to the equator, where temperatures are already close to or beyond the threshold of optimum production. The long-term effects on world agriculture productivity will be substantially negative. Developing countries are predicted to suffer an average 10 to 25 percent decline in agricultural productivity by the 2080s, assuming the so-called "business as usual" scenario in which greenhouse gas emissions continue to increase.

Of the world's 300 million people who live less than 5 meters above sea level, 80% are in developing countries: 200 million in Asia (90 million in China alone); 17 million in the Middle East and North Africa; 11 million in Sub-Saharan Africa; and 8 million in Latin America and the Caribbean. Rapid sea-level rise will threaten millions with inundation, as well as more severe flooding from storm surges and abnormally high tides.

Even a 1-meter rise will force up to 60 million people to become environmental refugees. And the affluent West, especially the United States, is only beginning to wake up to this global threat.

The U.S. should take the lead in reducing CO2 and other greenhouse gas emissions. We need to start working now to institute a multi-national, multi-faceted approach to climate change. If we do, we may even be able to keep the seas from rising.

Go as green as you can! Drive less. Cycle and walk more. Find out about how you can make your home and office more energy-efficient. You can start by replacing your incandescent bulbs with compact fluorescents. You'll lower your energy bill and keep nearly 700 pounds of carbon dioxide out of the air over each bulb's lifetime. Next time you buy a refrigerator, get one with the Energy Star label and reduce carbon dioxide pollution by nearly a ton in total.