Climate cycle

A climate cycle refers to natural cyclic variations in the earth's surface temperature, as indicated by temperature proxies found in glacier ice, sea bed sediment, tree ring studies or otherwise.

One difficulty in detecting climate cycles is that the earth's climate has been changing in non-cyclic ways over most scales of time. For instance, we are now in a period of anthropogenic global warming. In a larger time frame, the Earth is emerging from the latest ice age, which means that climate has been changing over the last 15000 years or so. And the Pleistocene period, dominated by repeated glaciations, has developed out of a more stable climate in the Miocene and Pliocene. All of these changes complicate the task of looking for cyclical behavior in the climate.

There are nevertheless several climate cycles which have been identified or hypothesized. These range from the cyclic behaviour of the Earth's orbital parameters (called Milankovich cycles) which are reflected in the long-term climatic record spanning several ice ages, through the Atlantic Multidecadal Oscillation, to short cycles such as the El Niño Southern Oscillation, the Pacific decadal oscillation, the Arctic oscillation, and the North Atlantic oscillation. The 11-year Sun spot cycle (the Hale cycle) may also be discernible in the climate record (see Solar variation).

Climate cycles are popular with media. One example is a 2003 study on the correlation between wheat prices and sunspot numbers.

There is also a 1500-year climate cycle observed in ice core data.

Other than the Milankovich cycles (and perhaps the Hale cycle), no climate cycle is found to be perfectly periodic and a Fourier analysis of the data does not give a sharp spectrum.

See also

• Temperature record
• Climate change
• Paleoclimatology
• Historical climatology
• Dansgaard-Oeschger events
• ice age
• Dendrochronology - The study of tree rings