We Are the Weathermakers

Chapter 4: Ice ages and Sunspots

Why doesn't the Earth retain all the heat it receives from the sun? On the other hand, why doesn't all the heat escape into space? The sun does not warm the atmosphere, however the reflections of darker objects do. Many scientists wonder what causes the Earth to heat and cool, although in 1941 Russian scientist Milutin Milankovich published what he believed to be the cause of ice ages. Milankovich stated that there are 3 cycles that determine the Earth's climate. The first is the planet's orbit around the sun, which is more so the shape of an oval than a perfect circle, whose shape changes every 100,000 years or so. The second cycle has to do with the tilt of the Earth's axis, which determines where most of the radiation is located. This cycle takes about 42,000 years to complete. Finally, the third cycle takes about 22,000 years to run its course and deals with the wobble of the Earth's axis, which determines the intensity of the seasons. Although these cycles only alter the amount of sunlight reaching the Earth annually by .1 of a percent, that can cause the Earth's temperature to change up to 5 degrees celsius. According to Milankovich's cycles, the Earth should be getting colder, although human pollution has caused the Earth's temperature to increase. With the help of these cycles, climatologists have continued to study why the Earth's climate has varied over time. In the early 1600's, Italian astronomer Galileo, with the help of one of the first ever telescopes, noticed dark spots on the sun. Although these sunspots are slightly cooler than the sun's surface, the Earth seems to warm up when there are more sunspots. The impact on the entire climate of the Earth may be too small to measure, although the variations of solar radiation and greenhouse gasses do have a large effect. Solar radiation affects the upper stratosphere, while greenhouse gasses warm the troposphere at the bottom where the concentration is highest. The stratospheric cooling and tropospheric warming are caused by the ozone hole and greenhouse gasses, respectively, as sunspots can not be responsible for either phenomenon. Finally, fossils can help us determine climate change. Due to the shift of steady climatic conditions, scientists have determined that these shifts have moved entire species from one side of a continent to another.

Questions:
1) What effect can sunspots have on Canada's climate?

2) Which of Milutin Milankovich's cycles has the greatest effect on climate change?

3) Since the Earth should be getting colder, what effect has human pollution really had on the Earth's temperature?