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Saturday, August 25, 2012

Degrees of Confusion-Another Modest Proposal


One of my biggest questions when trying to determine how much warming the globe has experienced due to the activities of man kind is what should be average?  By default, 1951 to 1980 is considered "average" because it was selected as "average" and is used as the base line for determining the impact of the Greenhouse effect.

With the gold standard of global surface temperature reconstructions, using the 1950 to 1980 baseline everyone is familiar with.

This is the same data with 1995 to 2010 used as a base line.  There is no difference in the global mean curve, but look at the two hemispheres.

This base line provides a better view of the internal oscillations between the hemispheres.  The northern hemisphere with less ocean volume and more land area has less thermal mass so would be more sensitive to changes in forcing.

Another minor issue is that land means above sea level.  As elevation increases the thermal mass of the air would decrease meaning the variation in temperature for a given unit of forcing would be greater at higher elevation than at sea level.

This may not be properly accounted for with the satellite measurements versus each other and the surface station data unless the weighting filters of each satellite temperature product perfectly match.

By using a Plain Vanilla Troposphere, the average of the lower and middle troposphere data products, the difference between the RSS and UAH data products is reduced, there there is some drift in the two products near the end of the data.

Working backwards from the more abundant and arguably more accurate data, the view of climate change, changes.  This view should reduce some of the increasing uncertainty.

This is a detrended version showing the 1951 to 1980 choice of baseline for determining climate change.  This just provides a different perspective of what changed what.  The temperature in the tropics had nearly a step drop around 1940 that may have produced the longer term reduction in the northern extra tropics.  That is not indicative of man made aerosols or other normally consider forcing, to my knowledge.  It is a bit of a mystery.
 This is the Plain Vanilla version of the UAH troposphere data, or the average of the lower and middle troposphere products.  All of the series were detrended and zeroed for the same series mean.  The 1979 to 1995 comparison above shows that the global mean in blue is higher than all the individual regional land and oceans series.
The same data from 1995 to 2012 shows that all the regional series warmed, nothing surprising there.

This plot focuses on the northern hemisphere.  The global is in the back, kinda hard to see, with the NH land and oceans in the fore ground.  The NH oceans were curving upward starting around 1985 following the El Chichon eruption then was depressed again in 1991 by the Pinatubo eruption.  The NH land and oceans stabilized slightly above global mean following the 1998 super El Nino.  In 1979, the beginning of the satellite data, the NH was nearly 0.4 degrees C below the global mean.  So did CO2 cause the warming or was the NH recovering from some other impact?

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