The Computation Of A Global Average Surface Temperature Anomaly

The gold standard of global warming (despite its inadequacies relative to the assessment of trends in the ocean heat content) is the global average surface air temperature anomaly and its annual trend over time. For example, it is claimed that a +2C anomaly must not be exceeded without major climate consequences (e.g. see).

However, what does a +2C anomaly actually mean.  To examine this issue, lets separate this temperature (which we will define as the global average surface air temperature anomaly as GASTA.  Then

GASTA = SSATA + TMaxA + TMinA 

where SSATA = the sea surface air (e.g. 2m) temperature anomaly;  TMaxA = the land surface air (e.g. 2m)  maximum temperature anomaly; and TMinA = the land surface air (e.g.2m)  minimum temperature anomaly.

We can approximate SSATA quite well, in general, from the sea surface temperature anomaly (SSTA).

Current SSTA values can be viewed http://www.osdpd.noaa.gov/ml/ocean/sst/anomaly.html and http://earthobservatory.nasa.gov/GlobalMaps/view.php?d1=MOD_LSTAD_M&d2=AMSRE_SSTAn_M

Daytime actual surface (but not TMaxA but related to this quantity) can be viewed at http://earthobservatory.nasa.gov/GlobalMaps/view.php?d1=MOD_LSTAD_M#

I have reproduced the NASA MODIS analyses below for March 2010 [on their website, analyses are available back to June 2002].

March 2010

Land Surface Temperature Anomaly

Sea Surface Temperature Anomaly

 

What is striking about these plots (which is true for the surface and any other level) is the large spatial variations in the anomalies.

 

What GISS, NCDC and CRU do to construct a global average is to use surface air temperature measurements to construct the anomalies (see the discussion in Chapter 3 of the CCSP 1.1 report).

 

There is a straightforward approach to examine the claims in studies such as

 

Menne, M. J., C. N. Williams, and M. A. Palecki (2010): On the reliability of the U.S. Surface Temperature Record, J. Geophys. Res., doi:10.1029/2009JD013094

 

that even poorly sited sparse surface air measurements can be used as part of the construction of a global average anomaly.

 

The challenge I am presenting in today’s post, is to encourage a quantitative comparison on a monthly basis of the anomalies seen in the above figures with the individual anomalies seen in the GISS, NCDC and CRU analyses. It is remarkable that such a comparison has not already been completed.  If a reader of this post is aware of such a comparison, please let us know.