Obliquity—The Tilt of the Earth

We all know that the tilt of the Earth accounts for the seasons, but many folks don’t know that the tilt, or obliquity, of the Earth has changed over time. During a period of 41,000 years, the tilt of the Earth’s axis changes from 22.1° to 24.6°. This wobble, like other facets of the Milankovitch Cycles, is caused by gravitational interactions with other planets.

Currently the tilt of the Earth’s axis is 23.4°, but 9,500 years ago when the Laurentide Ice Sheet had just about disappeared, the Earth’s tilt was at its maximum and the high latitudes were experiencing a greater differential of solar radiation than usual. So, the winters were long, dark, and cold and the summers were hot with the sun higher in the sky over Fairbanks than it will be this summer.

image from Wicander, Historical Geology, p 473.
It’s important to keep in mind that the tilt of the Earth doesn’t effect the amount of solar energy hitting the Earth, but only the distribution of that solar radiation by latitude. For this reason, the season-less low latitudes won’t really notice the change in the Earth’s tilt, but in the higher latitudes a small obliquity may prevent winter snow from melting in the summer when the temperatures don’t heat up as much.
image source: email forward of unknown origin

How does this relate to Climate? Critiques of Milankovitch

Climate Change