Maybe people are looking at the climate from too narrow a time span. Maybe the natural climate cycle is greater than what we have been recording for the last 150 yrs or so. The most detailed information exists since 1850, when methodical thermometer-based records began (Wikipedia).
Here gives a little bit about what may be involved in the cyclic climate pattern.
Climate cycle
From Wikipedia, the free encyclopedia
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 global warming that seems to be anthropogenic. 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, 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. [1].
There is also a 1500-year climate cycle claimed from ice core samples, and used in the global warming controversy.
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.
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mercy, peace and love
Kat