Saturday, September 20, 2008

Cooling Trend Continues

Although it has been little noted in the media the earth has been going through a cooling trend over the past nine months. During this period average global temperatures have declined by about .10 degrees Celsius (based on a 12-month moving average of the global temperature anomaly). Given the range of natural temperature fluctuations possible in the short term, most scientists would probably just dismiss this recent temperature movement as a random fluctuation.

While that view is very reasonable, I do consider that this is indicative of a long-term trend that will, in my view, produce a period of cooling for the next 30 years. As such, it is reasonable to keep track of this phenomenon as it unfolds so that more people can become aware that this is possible. The chart below shows the 12-month moving average global temperature anomalies for the actual data (from NOAA), for my own global temperature forecast based on the assumption of a cooling trend through 2038 counteracted by anthropogenic (human) warming caused primarily by greenhouse gas emissions and for Tamino's forecast as noted in other posts in this blog. Note that his forecast has been lagged one year so that it is directly comparable with the anomaly and anomaly forecast curves. Note also that my assumption of anthropogenic warming assumes that the climate sensitivity (or feedback effect) is zero and thus the position of the actual temperature anomaly above or below my forecast line potentially provides an indication of the actual climate sensitivity. The figure below shows the two forecasts and the actual temperature curve. The beginning date in the chart represents the approximate beginning of the current climate cycle:

Note how my forecast and Tamino's are, thus far, statistically indistinguishable. Tamino's forecast represents the IPCC consensus for an approximately 0.2 degrees increase in average global temperatures each decade. There are two things of note here - first, the actual global temperatures are now well below the consensus forecast as represented by Tamino's forecast and; second, the shape of my forecast and that of the actual temperature change are very similar but separated by about 12 months. Now, either or both observations could just be random events but it does give us something to focus on going forward.

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