The Greenhouse Effect—Vital for Life

The Greenhouse Effect—Vital for Life
A reason given for such changes is an intensification of the greenhouse effect, natural phenomena vital for life on earth. When energy from the sun reaches the earth, about 70 percent is absorbed, heating air, land, and sea. If it were not for this mechanism, the average surface temperature would be about zero degrees Fahrenheit (-18 degrees Celsius). Eventually, the absorbed heat is released back into space as infrared radiation, thus preventing the earth from overheating. But when pollutants change the composition of the atmosphere, less heat escapes. This can cause earth’s temperatures to rise.

Gases that contribute to the greenhouse effect include carbon dioxide, nitrous oxide, and methane, as well as water vapor. The atmospheric concentration of greenhouse gases has increased markedly over the past 250 years, since the start of the industrial revolution and the increased use of fossil fuels, such as coal and oil. Another greenhouse-enhancing factor seems to be the rising population of farm animals, whose digestive processes produce methane and nitrous oxide. Some researchers point to other causes of warming that they say occurred before humans could have influenced climate.

Just Another Fluctuation?
Skeptics of human-induced warming point out that earth’s temperature has undergone substantial fluctuations in the past. They point to the so-called ice ages, when the earth was supposedly much cooler than it is now; and in support of natural warming, they cite evidence that cold regions, such as Greenland, at one time supported vegetation that prefers warm areas. Of course, scientists concede that the further back they go, the more their certainty about climate diminishes.

What may have caused temperatures to vary significantly before human influence was a factor? Possible causes include sunspots and solar flares, which correlate with fluctuations in solar energy output. Additionally, earth’s orbit moves in cycles that take many thousands of years and that affect our planet’s distance from the sun. There is also the influence of volcanic dust and changes in oceanic currents.