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Sunday, May 26, 2013

To Remove or Not Remove, the Seasonal Cycle

Since I believe the impact of land use, agriculture wheat mainly, is grossly underestimated, I have been looking at the seasonal cycles for clues.  Most data has the seasonal cycle removed.  BEST uses absolute temperature and just averages, so the seasonal cycle remain in the data.  Leaving the seasonal cycle in doesn't have much impact on long term trends, but it does have impact on baseline anomalies.

Using the BEST NH data from 1900 to 2011 as a baseline, this chart compares using a 1900-1929 baseline versus using a 1981-2010 satellite era baseline.  That is a significant shift. 

Winter wheat crops require a consistent spring thaw to prevent snow mold and other problems.  Farmers can spread or spray ash, dust low albedo fertilizers etc. on snow to force the melt to match the crop.  The practice is also used to help prepare fields for earlier spring planting of a variety of crops.  This comparison shows exactly what you might expect if large scale agriculture was having an impact on Northern Hemisphere Land based climate.  Removing the seasonal cycle would tend to subdue the data possibly hiding an impact that is significant on a global scale. 

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