image credit: Robert Rhode (Wikimedia Commons); image source; larger image
This is the famous "Keeling curve" of carbon dioxide concentration in the atmosphere versus time, from about 1958 to about 2007, measured in Hawaii. Notice that the rate of warming (indicated by the slope of the blue line) increases slowly but steadily over time.
Carbon dioxide is an important greenhouse gas. Greenhouse gases absorb the infrared radiation given off by Earth. This absorbed radiation is promptly re-emitted in all directions; much of it returns to Earth, raising the temperature of its surface by a substantial 33°C.
Carbon dioxide is produced by burning fossil fuels. As more countries industrialize, the use of fossil fuels increases, as does the amount of carbon dioxide in the atmosphere
The inset in the graph shows the annual cycle: For six months, plant photosynthesis absorbs carbon dioxide from the atmosphere, and the curve goes down; then, for the next six months, the decay of dead plants returns carbon dioxide to the atmosphere, and the curve goes up.
To learn more, visit Greenhouse Effect and also this UCAR page.
Ice over the Poles
Visit Ice over the Poles for an interesting article on ice at the Poles--both sea ice at the North Pole, and land ice on Antarctica. Be sure to see the explanation of how melting of ice sheets or glaciers can provide "positive feedback" and increase the rate of warming.