An Introduction to Global Warming
Global warming is real, and human beings have something to do with it. We don't have everything to do with it; but we can't stop it, and we couldn't even slow it down enough to measure our efforts if we tried.
Figure 2.1 is a chart of various estimates of planetary temperature going back to 1610. That signal date marks Galileo's invention of the telescope. One of the first things Galileo used it for was to view the sun. (That he didn't immediately go blind is testimony to his wisdom: he knew to project the image rather than to look at it directly.) Every few months or weeks he noticed that a black spot, or a few of them, would appear on the sun's surface.
Whether a person believed in an earth-centered universe or a heliocentric one (a view of Jupiter and its moons soon convinced Galileo of the latter), everyone pretty much agreed that the sun warmed the earth. So the appearance of black spots became a curiosity worth recording: Would a darker sun create a cooler planet?
We now know that the opposite is true. A sun with many spots is a hotter sun because the dark regions are surrounded by larger, whiter areas that are more energetic than the quiescent state. Since that discovery, myriad scientists have matched the earth's temperature to the output of the sun. This isn't exactly rocket science. If there were no match, the basic theory of climatology would be wrong, a theory that simply states that the sun is the cause of our climate.
A review of sunspot records is one way to back-calculate the earth's temperature before the general use of thermometers, which dates back to the mid-1800s. But there are other climate “proxies.” The width of tree rings, for example, is related to total rainfall and summer temperature. Plants leave fragments, including long-lasting pollen, in the bottom of lakes, and shallow lakes “turn over” every year, creating annual striations, called varves, that can be counted back in time. Shifts in pollen assemblages trapped in varves from