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Tuesday, December 3, 2013

Climate "Sensitivity" for the Instrumental Period

OOPS Spreadsheet error on the BEST Tmax Tmin charts - See comment:  2000 years of Climate is a quick reverse splice to paleo using only one paleo reconstruction for the Indo-Pacific Warm Pool.  Based on that quick reconstruction, "sensitivity" using ln(CO2/CO2ref) as a reference appears to be ~1.6 C degrees.  Only one paleo reconstruction along with BEST and CET temperatures scale to global mean sea level and the Indian Ocean SST was used since the paleo and longer term temperature records just provide an estimate of the mean.  So let's look at some other instrumental data.

Using the dT(CO2) as a reference compared to the ERSSTv3b Northern Hemisphere SST a "sensitivity" of 1.23 C per doubling produces a zero mean for the residual.

The Southern Hemisphere SST requires a "sensitivity" of 1.6C per doubling to zero the residual. Now here is the fun part.

The main perturbation in the residuals bottoms out around 1910.  The less sensitive NH rebounds more quickly and synchronizes with the SH for a peak in 1941 then there is a weak oscillation. 

Comparing with volcanic there is obviously a correlation but the internal mixing is more than just a little complex.  An 8 year lag pretty well lines up the perturbation but the different recovery timings can almost erase an impact and shift the lag. 

With the land data there is another issue related to what exactly does Tave mean.  To use the BEST and CET data for bridge to paleo reconstructions I removed part of the "land" amplification by scaling the data to a common 1955-2011/12 baseline.  People relying on the "land" for a higher climate sensitivity will not like that.  So let's look at BEST Tmax versus Tmin.

Using the 1.23 "sensitivity" based no the northern hemisphere oceans I get this "fit".  The zero mean for Tmax is about 0.15C below what should be the mean and the Tmin zero is about 0.8C above what should be the mean.  Pretty obviously there is a difference between the Tmax and Tmin responses do to "other" things.

Smaller chart below replaced with above due to spreadsheet error.
Comparing the residuals after removing the ~1.23C CO2 reference there is a nice long recovery period that can be due to land based ice melt, land use changes, instrumentation issues, but likely not due to direct atmospheric forcing.  Tmin contributes 50% to Tave land which contribute 30% to the global mean temperatures.  That is ~2C degree since 1950 or 1C impact on Tave and .3C impact on global T mean.  That doesn't include the ~0.15C that may be due to a longer term secular rise in ocean temperatures that may be attributed to the period formerly known as the Little Ice Age.  Not too surprisingly 0.3 C is twice 0.15C which is consistent with "normal" land amplification based on specific heat capacity differences.  Unlike comparing the actual diurnal temperature range, this residual comparison doesn't have a trend reversal in ~1985. Much smaller reversal almost flat. 

For the higher sensitivity fans.  Note: the background Tmin is inverted in the following chart - corrected below.

Focusing on Tmax produces a sensitivity of 2.2 C.  For the natural variability/LIA fans.

Zeroing the Tmin residuals results in a negative 4.1 C sensitivity.   Why? Because there was a spreadsheet error :)  It is actually a +4.1 sensitivity the small chart is replaced with the larger above.

Because Tmin is amplified by other than atmospheric radiant forcing.  By scaling Tmin by 0.5 there is nearly a perfect fit with the 45S-45N SST until 1900 when the reliability of temperature records degrades.  Comparing a Tave to SST where only the Tmax portion is related to atmospheric forcing produces a fruit salad.

So when comparing Instrumental period data to climate "sensitivity" there is more to be considered.

Update:  It took a while to beat OpenOffice into submission but this might be of interest to some of the Stadium Wave fans.

 This is 10 degree latitude band SST using the ERSSTv3b Climate Explorer mask with the "average" sensitivity removed using the 1951-2012 CO2 reference.  I stopped at 45S and 45N since this is the main energy band.  The smoothing is 11 year cascade to get rid of most of the ENSO type wiggles. 

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