Difference between revisions of "Climate cycles"
Lonewolf2852 (talk | contribs) (New page: Climate cycles are a natural occurrence in which temperatures tend to vary slightly over hundreds of years. Although these cycles are natural and do exist the recent increase in temperatur...) |
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| − | Climate cycles are | + | Climate cycles are natural trends in which temperatures fluctuate on large time-scales, ranging from minor fluctuations over a few centuries to massive shifts in climate over several tens of thousands of years. |
| + | Using proxy data from various natural sources (including deuterium content in ice cores, calcium content and thickness of sea shells and tree ring growth data) we can establish that these cycles do exist, and that they occur for several reasons, perhaps the most prominent of which is the Milkanovitch cycle. | ||
| + | However, whilst the variation over large time-scales is extreme (deviating from the long-term average by as much as ten degrees Celsius at a time), the changes are usually very gradual and take place over many millennia. | ||
| + | |||
| + | The existence of these climate cycles is often used as a contradiction of the theory of anthropogenic global warming, or man-made climate change. | ||
| + | However, this argument does not stand up to scrutiny. It can be seen that the Earth is currently in the middle of a time of peak temperatures during which little or no warming should be expected. | ||
| + | This contradicts the observed facts, which indicate ~0.76 degrees Celsius of warming (with error bounds of 0.2 degrees Celsius either way) over the past century and a half or so. | ||
| + | Changes of such magnitude, when natural, normally take place over much longer time-scales. | ||
| + | |||
| + | This is not to say that the current warming period could not be natural. | ||
| + | However, such a theory is unsupported by the evidence. | ||
Revision as of 23:20, September 26, 2007
Climate cycles are natural trends in which temperatures fluctuate on large time-scales, ranging from minor fluctuations over a few centuries to massive shifts in climate over several tens of thousands of years. Using proxy data from various natural sources (including deuterium content in ice cores, calcium content and thickness of sea shells and tree ring growth data) we can establish that these cycles do exist, and that they occur for several reasons, perhaps the most prominent of which is the Milkanovitch cycle. However, whilst the variation over large time-scales is extreme (deviating from the long-term average by as much as ten degrees Celsius at a time), the changes are usually very gradual and take place over many millennia.
The existence of these climate cycles is often used as a contradiction of the theory of anthropogenic global warming, or man-made climate change. However, this argument does not stand up to scrutiny. It can be seen that the Earth is currently in the middle of a time of peak temperatures during which little or no warming should be expected. This contradicts the observed facts, which indicate ~0.76 degrees Celsius of warming (with error bounds of 0.2 degrees Celsius either way) over the past century and a half or so. Changes of such magnitude, when natural, normally take place over much longer time-scales.
This is not to say that the current warming period could not be natural. However, such a theory is unsupported by the evidence.