The Earths surface temperature has risen by about 1 degree Fahrenheit in the past century, with accelerated warming during the past two decades. There is new and stronger evidence that most of the warming over the last 50 years is attributable to human activities.
Human activities have altered the chemical composition of the atmosphere through the buildup of greenhouse gasesprimarily carbon dioxide, methane, and nitrous oxide (Wezp.com Politics category). The heat-trapping property of these gases is undisputed although uncertainties exist about exactly how earths climate responds to them.
Energy from the sun drives the earths weather and climate, and heats the earths surface; in turn, the earth radiates energy back into space. Atmospheric greenhouse gases (water vapor, carbon dioxide, and other gases) trap some of the outgoing energy, retaining heat somewhat like the glass panels of a greenhouse.
Without this natural greenhouse effect, temperatures would be much lower than they are now, and life as known today would not be possible. Instead, thanks to greenhouse gases, the earths average temperature is a more hospitable 60F. However, problems may arise when...