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Abstract: The rise in global average temperature over the last century has halted since roughly the year 2000, despite the fact that the release of CO2 into the atmosphere is still increasing. It is suggested here that this interruption has been caused by the suspension of the near linear (+ 0.5 °C/100 years or 0.05 °C/10 years) temperature increase over the last two centuries, due to recovery from the Little Ice Age, by a superposed multi-decadal oscillation of a 0.2 °C amplitude and a 50~60 year period, which reached its positive peak in about the year 2000—a halting similar to those that occurred around 1880 and 1940. Because both the near linear change and the multi-decadal oscillation are likely to be natural changes (the recovery from the Little Ice Age (LIA) and an oscillation related to the Pacific Decadal Oscillation (PDO), respectively), they must be carefully subtracted from temperature data before estimating the effects of CO2.
Excerpts:
It is at least problematic, therefore, to consider this near linear increase in temperature during the 19th and 20th centuries as mainly due to CO2.
A halt and even a slight decrease in the rising trend after 2000 can therefore be expected, on the basis of this spectral analysis.
It is quite likely, therefore, that the near linear increase due to LIA recovery has been temporarily overwhelmed by the multi-decadal oscillation, which had reached a positive peak in about the year 2000.
Conclusion:
It is likely that both the near linear increase and multi-decadal oscillation are primarily natural changes. Thus, in order to estimate the effects caused by CO2 over the last two centuries, it is important to isolate these natural components of climate change from real temperature data.
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