The Earth is habitable because it has a protective blanket of greenhouse gases surrounding it. This blanket traps heat from the sun and allows the Earth to stay at an optimal temperature for life to exist.
If this blanket becomes too thick or thin, the Earth's temperature will respond by becoming too hot or cold for human life. Currently, the blanket is becoming too thick because of the addition of billions of metric tons of global warming pollution, mainly carbon dioxide, that is being released into the atmosphere by human activities.
Roughly 30 percent of the sun's heat that strikes the Earth is reflected back into space by clouds, particles in the atmosphere and reflective ground surfaces, such as snow, ice and ocean surf.
The remaining 70 percent is absorbed by the land, air and oceans. This absorption warms the Earth's surface and atmosphere, allowing life to exist.
The heat absorbed by the Earth, ocean and atmosphere is not retained forever, as this would cause the Earth to increase in temperature until it was unbearable. Rocks, air and sea emit some of the heat they absorb, much of which leaves the atmosphere and is lost to space.
A small component of the heat, however, is trapped by carbon dioxide and other greenhouse gases in the atmosphere and is returned to the Earth's surface. This process is called the greenhouse effect. Under normal conditions, the greenhouse effect is positive as it allows the planet to maintain an optimal temperature for life to exist at around 15 C (59 F). Without the greenhouse effect, the earth's average temperature could be as low as -18 C (0 F).
While the greenhouse effect is vital for life to exist on this planet, we are increasing the greenhouse effect, causing the planet to overheat. As we cut down trees across the globe and burn fossil fuels by driving cars and running power plants, we release billions of metric tons of global warming pollution to the earth's atmosphere where it can remain for hundreds of years.
We release about 30 billion metric tons of carbon dioxide to the atmosphere every year. This massive increase in greenhouse gases is overpowering the earth's natural ability to regulate temperature, resulting in a warmer planet.
As the global population grows and levels of development and consumption increase, the amount of greenhouse gases being produced will continue to grow unless we act quickly. Many scientists have warned that we are fast approaching the point of no return and that if we don't cut global greenhouse gas emissions before we pass a tipping point, preventing dangerous global warming may be impossible.