Time Constant, and Sensitivity of Earth’s Climate System to a step change
Background
There is evidence of a recent abrupt drop in planetary temperature based on the NASA data. (See below comment and above comments for details.) Although regional meteorological observations (in both hemispheres), supports a drop in planetary temperature, additional data is required to confirm the change is real.
When there is more data, it should be possible to determine the magnitude of the forcing function change which appears to be related to the recent solar magnetic cycle changes and to determine the final equilibrium temperature (assuming a long term solar magnetic cycle change.)
This paper is a good overview of the science and technical issues, concerning the planet’s response to a step change in forcing. It examines planetary temperature changes to step changes in forcing from volcanic eruptions, to estimate the planetary time constant to be 5 years +/- 1 yr. In addition, it finds evidence for a planetary response to a forcing change of 0.30 ± 0.14 K/(W m-2).
The current evidence of an abrupt change in planetary temperature supports a short time constant. (See the paper for details as to why the planet has a short time constant. The reason is that the layers of the earth's ocean do not mix due to density differences. This paper's findings is consistent with paleoclimatic evidence of abrupt climate changes. It is also consistent with a basic text book I have on Atmospheric Science.)
Heat Capacity, Time Constant, and Sensitivity of Earth’s Climate System, S. E. Schwartz
http://www.ecd.bnl.gov/steve/pubs/HeatCapacity.pdf
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In contrast to these studies (my comment: which assert a time constant of 40yr to 400 yrs) there is a growing body of observational evidence to suggest that the time over which changes in climate can take place can be quite short, just a few years. High-resolution studies of temperature change in ice cores as inferred from isotope ratios and other variables demonstrate substantial widespread temperature change in periods as short as five to ten years [Taylor et al., 1997; NRC, 2002; Alley et al., 2003].
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…cooling of global proportions in 1816 and 1817 followed the April, 1815, eruption of Mount Tambora in Indonesia. Snow fell in Maine, New Hampshire, Vermont and portions of Massachusetts and New York in June, 1816, and hard frosts were reported in July and August, and crop failures were widespread in North America and Europe – the so-called "year without a summer" (Stommel and Stommel, 1983). More importantly from the perspective of inferring the time constant of the system, recovery ensued in just a few years. …
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From an analysis of the rate of recovery of global mean temperature to baseline conditions between a series of closely spaced volcanic eruptions between 1880 and 1920 Lindzen and Giannitsis [1998] argued that the time constant characterizing this recovery must be short; the range of time constants consistent with the observations was 2 to 7 years, with values at the lower end of the range being more compatible with the observations.
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… time constant of about 2.6 years is inferred from the transient climate sensitivity and system heat capacity determined by Boer et al. [2007] in coupled climate model simulations of GMST (My comment GMST is global mean surface temperature) following the Mount Pinatubo eruption. Comparable estimates of the time constant have been inferred in similar analyses by others [e.g., Santer et al., 2001; Wigley et al., 2005].
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Comments:
Based on the NASA Land + Ocean (Above Normal)
Average (2003 to Jan, 2008) = 0.55C (Above deemed normal.)
Temperature Jan, 2008 = 0.12C (Above deemed normal, 3.6 Sigma significant.)
Change in planetary temperature over about a year = -0.43C