Humanity is conducting an unintended, uncontrolled, globally pervasive experiment whose ultimate consequences could be second only to nuclear war. Fossil fuel burning, deforestation, and the release of industrial chemicals are rapidly heating the Earth to temperatures not experienced in human memory. Environmentally we have reached a point of unprecedented damage. Limiting global heating and climatic change is the central environmental challenge of our time. If it does not change, human health, birds fish, and many types of ecosystems will be permanently harmed.
The greenhouse effect results from the buildup in the atmosphere of gases which absorb heat. To maintain a constant average temperature, the Earth must radiate heat to space. Greenhouse gases like carbon dioxide (CO2) and methane (CH4) absorb a part of this heat energy and radiate it back to the surface of the planet, trapping it in the lower atmosphere (troposphere). This process raises the temperature of the atmosphere near the Earth, which in turn raises sea level, increases evaporation and precipitation to affect global cloud cover; and thereby alters the distribution of climate across the surface of the planet. An increase in average global temperature of 0.7 C has already been measured, and present rates of emission of greenhouse gases are committing the Earth to an additional warming of about 0.3 C per decade. We are also adding small particles and droplets called aerosols that reflect light back into space and tend to cause some areas to cool.
It is because they trap heat like glass in a greenhouse that these gases received their name -- the greenhouse gases. They are vitally important for life. Earth has a natural greenhouse effect due to the presence of CO2 and water vapor. If Earth's atmosphere did not contain these gases, its temperature would be 33 C lower. The natural level of these gases make life as we know it possible.