The earth is warmer than it would be in the absence of the greenhouse gases in the atmosphere. Most of the greenhouse effect is natural and caused predominantly by water vapor and water droplets in clouds, then followed by, in diminishing order of importance, carbon dioxide, methane and other minor gases in the air. Since the Industrial Revolution, carbon dioxide concentration has been increasing in the air owing to human actions like coal combustion and deforestation, with a rapid rise in the last several decades. The increase in the air’s carbon dioxide would suggest a rising global temperature, all other things being equal. However, it is difficult to calculate the response of the climate system to the small amount of energy added by the presence of extra carbon dioxide in the air. The reason is that climate is a complex, dynamical and non-linear system, with positive and negative feedbacks, and knowledge of the causes and responses of climate change is presently insufficient to give an accurate response.
This article appeared in the 2000 Proceedings, Southern Weed Science Society, Volume 53, pp. lxx to lxxii.
This work was supported by the Massachusetts Space Grant Consortium (MIT grant 16717049) and the National Aeronautics and Space Administration (grant NAG5-7635).