From a January 5, 2010 Wall Street Journal column by Pete du Pont:
Al Gore said the other week that climate change is "a principle in physics. It's like gravity. It exists." Sarah Palin agreed that "climate change is like gravity," but added a better conclusion: Each is "a naturally occurring phenomenon that existed long before, and will exist long after, any governmental attempts to affect it."
Over time climates do change. As author Howard Bloom wrote in The Wall Street Journal last month, in the past two million years there have been 60 ice ages, and in the 120,000 years since the development of modern man, "we've lived through 20 sudden global warmings," and of course this was before--long before--"smokestacks and tail pipes."
In our earth's history there has been both global warming and global cooling. In Roman times, from 200 B.C. to A.D. 600, it was warm; from 600 to 900 came the cold Dark Ages; more warming from 900 to 1300; and another ice age from 1300 to 1850. Within the past century, the earth has warmed by 0.6 degree Celsius, but within this period we can see marked shifts: cooling (1900-10), warming (1910-40), cooling again (1940 to nearly 1980), and since then a little warming. The Hadley Climatic Research Unit global temperature record shows that from 1980 to 2009, the world warmed by 0.16 degree Celsius per decade.