Over the past 100 years, as we have put more and more carbon dioxide into the atmosphere, the earth has warmed by about 1 degree F (0.6 degrees C). Although the size of this warming doesn't sound very big, it is scary for two reasons: 1) the rate of increase is fast, and 2) it shows the potential of far greater warming in this century.
To the left is a graph of the earth's average surface temperature over the past 120 years. Note that the units on the left are the difference between that year's temperature and a long term average. This chart shows the earth warming about one degree F over the past hundred years, with the fastest warming in the past 20 years. To see how this compares with past climate changes, click on the climate past link above.
We are already seeing the effects of this warming. Worldwide, glaciers are rapidly retreating(1,2,3), the sea level has risen slightly (1,2,3), growing seasons are longer (1), and birds are migrating earlier (1). The warming trend is not even, as the regions near the poles are warming faster(1).
To understand the basics of why this is happening, click on the greenhouse effect above. To see how this will play out in this next century, click on climate future above. To see what the climate history can tell us, look at climate past.
