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Climate Variability and Change

Why does climate change?

Last updated 21 June 2005
Originally answered 18 April 2000

Full Question

Why does climate change?

Answer

Climate fluctuations are the result of complex interactions of a number of factors, including natural changes such as variations in the Earth’s orbit (known as Milankovitch theory), volcanic eruptions, fluctuations in solar energy and anthropogenic (human-caused) influences, such as the burning of fossil fuels, which releases so-called greenhouse gases into the atmosphere.

Climate changes can occur over periods as short as a year or as long as several thousand years. For more information, take a look at the following resources:

• Causes of Climate Change.  Chapter 2 from the Global Climate Change Student Guide (1999) by Joe Buchdahl and published by the Atmosphere, Climate and Environment Information Programme of Manchester Metropolitan University (UK).
• Climate TimeLine. Designed as an online tool allowing users to examine climate change and variability at different time scales.  Posted by the National Geophysical Data Center.
• Climate Change Science: An Analysis of Some Key Questions. By (2001) the National Research Council.  (2001)   
• The Climate System: an Overview.  Chapter 1 of  Climate Change 2001: Working Group I: The Scientific Basis, report of the Intergovernmental Panel on Climate Change.
• Our Changing Climate [PDF] (especially the sections "Earth's Climate: A Dynamic System" and "Why Does Our Climate Change".  Brochure (dtd 1997) from the University Corporation for Atmospheric Research.
• Astronomical Theory of Climate Change.  Posting (last updated 9 September 2003) from the National Oceanic and Atmospheric Administration (NOAA).   See also On the Shoulders of Giants: Milutin Milankovitch, article (undated) from NASA’s Earth Observatory.

Are ozone depletion and climate change linked?

Last updated 08 August 2002
Originally answered 8 August 2002

Full Question

Are ozone depletion and climate change linked?

Answer

According to the UNEP/WMO “Scientific Assessment of Ozone Depletion: 2002,” ozone-layer depletion and climate change are linked in a number of ways, but ozone depletion is not a major cause of climate change. The stratosphere cools when ozone is destroyed because there is less ozone to absorb UV radiation. This cooling in turn affects air motions and chemical processes that are related to climate. In addition, some ozone-depleting gases (and, indeed, ozone itself) are also heat-absorbing “greenhouse gases,” so they play a dual role in climate change and ozone depletion. The potential contributions to climate change from ozone and ozone-depleting gases is smaller than from changes in other important atmospheric gases.