GLOBAL WARMING

The Planet is Heating Up—and Fast
Glaciers are melting, sea levels are rising, cloud forests are drying, and wildlife is scrambling to keep pace. It's becoming clear that humans have caused most of the past century's warming by releasing heat-trapping gases as we power our modern lives. Called greenhouse gases, their levels are higher now than in the last 650,000 years.

What Causes Global Warming?
Scientists have spent decades figuring out what is causing global warming. They've looked at the natural cycles and events that are known to influence climate. But the amount and pattern of warming that's been measured can't be explained by these factors alone. The only way to explain the pattern is to include the effect of greenhouse gases (GHGs) emitted by humans.
Signs are Everywhere
The planet is warming, from North Pole to South Pole, and everywhere in between. Globally, the mercury is already up more than 1 degree
Fahrenheit (0.8 degree Celsius), and even more in sensitive polar regions.
Has Global Warming Been Exaggerated?
The warming of Earth's surface and oceans over the past century is very well documented, and climate research shows that most of the warming in the past half century results from manmade greenhouse gases. In recent years, global warming has been the subject of a great deal of political controversy. As scientific knowledge has grown, this debate is moving away from whether humans are causing warming and toward questions of how best to respond.

What Can We Do?
The evidence that humans are causing global warming is strong, but the question of what to do about it remains controversial. Economics, sociology, and politics are all important factors in planning for the future.

http://green.nationalgeographic.com/environment/global-warming/