New Computer Fund

Friday, February 20, 2015

CET and Volcanic Forcing

I was playing with Volcanic forcing when Tony Brown put up a post on Climate Etc. about his Central England Temperature (CET) reconstruction using weather notes in diaries etc. for fill in the blanks to some extent pre-instrumental.  The CET record is more popular with skeptics especially of British origin and like any "local" temperature record has its good points and bad points.  So I made this rather busy chart.

 One of the major pluses for CET is it marine climate influence due to the Gulf Stream.  One of its minuses is it high latitude so variations in the Northern jet stream create huge swings relatively speaking in average temperature.  I have used a normal 5 year moving average of the CET annual and the BEST data I have is smoothed with a cascading 27 month average.  The three cascade stages would be roughly equal to a 6 year average.  I only used the Crowley and Unterman 2013 Northern Hemisphere volcanic data with simple 20% decay.  Then I roughly scaled the volcanic forcing with the 1815 1840 events.  Since I was using anomaly for the BEST data I added a +0.4 C offset to the volcanic to roughly match that same period.  Then I include the Law Dome CO2 reconstruction with a "sensitivity" of 1.1 C to roughly match the BEST 30S-30N temperature data.

The Berkeley Earth Surface Temperature (BEST) project noted the greater than expected amplification of the 30N-60N land temperature data.  This chart shows that at times, CET is more influenced by the amplified region in blue but appears to revert to the more "global" representative 30S-30N region.  The fit with the Volcanic forcing is the typical tease where some areas the fit is great and some areas not so great.  There is a lot more noise with some of that amplified in the northern higher latitudes which contributes to that less than ideal fit.  The Crowley and Unterman volcanic data includes quite a few smaller events ignored in previous reconstructions as well as so major events that were just neglected for whatever reason.  The extra information doesn't "fix" all the issues but it does reduce some o the more glaring inconsistencies.   For example 1912 now has an event to match its temperature dip,  Novarupta which was  VEI 6.

The CMIP5 models appear to include a 1912 volcanic event, but smaller than the 1904 event which appears to be Mount Lolobau which was a VEI 4.  So there is a significant difference between C&U volcanic and the volcanic used for CMIP5.  Note that the +0.4 offset I used is about the same as used for CMIP5.

The reason for all this is was there really a Little Ice Age and if so when did it end?

Since I "calibrated" my volcanic forcing to the 1810 to 1840 period which produced the +0.4 offset, I would be of the opinion that a period of cooler than "normal" temperatures due to volcanic forcing wouldn't be over until temperatures returned to the pre-volcanic forcing level.  That would be roughly 1930 to 1940 a period with much lower than "normal" volcanic activity.   Since the climate science community "picks" circa 1900 as the end of the LIA, they think "normal" is about 0.4C lower than I do, even though their modeled forcing tends to agree with me.  0.4 C is about half of the estimated AGW claimed which makes some of their projected impacts a bit hard for me to swallow.

Looking at the entire Crowley and Unterman 2013 NH data it seems perfectly reasonable to assume that more volcanic activity would lead to lower than normal temperatures and less would lead to warmer than normal temperatures.  What really is normal though would depend on what is "normal" volcanic activity .

This overlay of the Oppo et al. 2009 Indo-Pacific Warm Pool that seems to agree with my circa 1930 to 1940 exit from the LIA.  With instrumental data such as it is, CET and BEST, extending back to the mid 1600s to 1700s, the Mann "Global" temperature change reconstruction looks less and less likely.

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