The world's climate has always been highly variable. Many changes are driven by natural factors, but others are now the result of human activities. Carbon dioxide is an important greenhouse gas and increasing concentrations lead to a heating of the atmosphere.
Vegetation contains carbon that is released as carbon dioxide when the vegetation decays or burns.
The amount of carbon dioxide in the atmosphere will double during the twenty-first century if the current trends in emissions continue, with further increases thereafter. The amounts of several other greenhouse gases will increase substantially as well. Natural changes in climate Large volcanic eruptions put tiny particles in the atmosphere that block sunlight, resulting in a surface cooling of a few years duration. Variations in ocean currents change the distribution of heat and precipitation. Over longer time spans, tens or hundreds of thousands of years, natural changes in the energy received from the sun, or in the balance of greenhouse gases or dust in the atmosphere have caused the climate to shift from ice ages to relatively warmer periods, such as the one we are currently experiencing.