Humanity has been adding gases to the atmosphere that tend to warm the earth, known as "greenhouse gases." We are also adding small particles and droplets called aerosols that reflect light back into space and tend to cause some areas to cool. In the coming decades, we are likely to continue to change our atmosphere. Because the greenhouse gases that warm the earth stay in the atmosphere longer than the aerosols that cool the earth, the earth's average temperature is likely to continue to warm.
Past
The temperatures of the Earth and any other planet depends mainly on (1) the amount of sunlight received, (2) the amount of sunlight reflected into space, and (3) the extent to which the atmosphere retains heat.
Future
The extent and speed at which humanity changes the climate will depend to a large extent on the rate at which society adds additional greenhouse gases to the atmosphere. Until a few decades ago, energy consumption grew at about the same rate as the Gross National Product.
Variability
The Earth's climate is dynamic and has been undergoing change since the Earth was formed. Fluctuations in temperature and precipitation patterns are natural consequences of this variability. But evidence is mounting that current changes in the climate system exceed what might be expected due to natural causes alone.
