External Forcing

External forcing factors are processes external to Earth and its atmosphere that influence Earth's climate. They include galactic variations, orbital variations, and sunspots.

Dark central region of a planet-sized sunspot. The bright filaments that extend into the sunspot have dark cores that are thousands of kilometers long but only about 100 km wide.

Göran Scharmer, the Royal Swedish Academy of Sciences, Swedish Solar Telescope on La Palma

 Galactic Variations

 Orbital Variations

 Sunspots

 

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Milankovitch cycles Last Updated on 2010-07-07 16:09:56 Milankovitch cycles refer to long term variations in the orbit of the Earth which result in changes in climate over periods hundred of thousands of years and are related to ice age cycles. Once Isaac Newton described his laws of motion and of gravity, the orbit of each planet became predictable, not only under the influence the Sun, but the much weaker influences of all the other planets and the Moon as well. Milutin Milankovitch did not discover the cycles, nor was he the first to calculate their changes. He did, though, improve on the methods of calculating them and relating them to Earth’s climatic variations. Here is a brief description of the three cycles. Precession (also called Precession of the Equinoxes): the gravitational pull of the Sun and Moon on Earth’s equatorial bulge causes the poles to slowly wobble. Over 25,800 years, the polar axis... More »
Model Climate Sensitivity Last Updated on 2010-02-18 00:00:00 The response of climate to a perturbation such as a change in carbon dioxide concentration, or in the flux of energy from the sun, can be divided into two factors: This article is drawn from Chapter 4 of CCSP, 2008: Climate Models: An Assessment of Strengths and Limitations. A Report by the U.S. Climate Change Science Program and the Subcommittee on Global Change Research [Bader D.C., C. Covey, W.J. Gutowski Jr., I.M. Held, K.E. Kunkel, R.L. Miller, R.T. Tokmakian and M.H. Zhang (Authors)]. Department of Energy, Office of Biological and Environmental Research, Washington, D.C., USA, 124 pp. A Table of Contents of other articles drawn from the report is included before the references section of this article. “radiative forcing” due to the perturbation in question; and, “climate sensitivity,” characterizing... More »