Guest post by Dr. Roger Pielke Senior
As discussed in the post
the global annual average surface temperature trend has become the icon of communicating climate change to the policymakers and even within the climate science community.
However, as I have written previously; e.g. see
Pielke Sr., R.A., 2003: Heat storage within the Earth system. Bull. Amer. Meteor. Soc., 84, 331-335
and as presented elsewhere; e.g. see
Misconception #2: The global average annual temperature average is an appropriate metric to diagnose global warming.
Global warming, of course, is just a subset of climate variability and long-term change [see], which I will discuss further in a later post.
A change in heat (e.g. global warming) is defined in Joules [not degrees Celsius by itself) and can be written for the climate system as
ΔH = MA * [CA * ΔT + L Δq] for the atmosphere + MO* [CO* ΔT ] for the ocean + ML* [C L* ΔT + heat from phase changes of soil water] for land + MI* [CI * ΔT + heat from phase changes of ice] for continental glaciers and sea ice
where H is heat in Joules, M, C and ΔT represents the mass, the heat capacity and the temperature change for the respective components of the climate system, respectively. L is the latent heat of vaporization and q is the specific humidity.
As clearly overviewed in the excellent post on the Air Vent
where a figure from that weblog is reproduced below
the ocean is a much larger reservoir of heat changes. A similar plot for land, and the continental glacier and sea ice would show a similar very large disparity between the oceans and the other reservoirs.
Where does the global annual average surface temperature trend fit into this framework? I present four reasons below that document why this temperature fails to accurately diagnose global warming. Other reasons are discussed in several of our research papers; e. g. see
Pielke Sr., R.A., C. Davey, D. Niyogi, S. Fall, J. Steinweg-Woods, K. Hubbard, X. Lin, M. Cai, Y.-K. Lim, H. Li, J. Nielsen-Gammon, K. Gallo, R. Hale, R. Mahmood, S. Foster, R.T. McNider, and P. Blanken, 2007: Unresolved issues with the assessment of multi-decadal global land surface temperature trends. J. Geophys. Res., 112, D24S08, doi:10.1029/2006JD008229.
First, as seen in the above figure from the Air Vent the absolute value [MA * [CA * ΔT + L Δq] for the atmosphere] << absolute value [MO* [CO* ΔT ] for the ocean]
Thus we can define that
Global Warming is an increase in the heat (in Joules) contained within the climate system. The majority of this accumulation of heat occurs in the upper 700m of the oceans.
Global Cooling is a decrease in the heat (in Joules) contained within the climate system. The majority of this accumulation of heat occurs in the upper 700m of the oceans.
Even over the ocean, the surface air temperature (marine air) is only a small part of this heat accumulation, and then only if it is well correlated with temperatures over at least a few meters of depth.
Second, over land, there is another issue, heat is not only contained in the temperature but also the moisture content of the air. The moist enthalpy [CA * ΔT + L Δq] is the appropriate measure of atmospheric heat content; e.g. see
Pielke Sr., R.A., C. Davey, and J. Morgan, 2004: Assessing “global warming” with surface heat content. Eos, 85, No. 21, 210-211.
Thus, in using the global annual average surface air temperature trend to diagnose global warming and co0ling, the contribution to heat changes of the air by concurrent water vapor changes [L Δq], an important fraction of the heating/cooling is missed.
Third, there is issue of the height at the air temperature measured? As we have shown in
Steeneveld, G.J., A.A.M. Holtslag, R.T. McNider, and R.A Pielke Sr, 2011: Screen level temperature increase due to higher atmospheric carbon dioxide in calm and windy nights revisited. J. Geophys. Res., 116, D02122, doi:10.1029/2010JD014612.
Lin, X., R.A. Pielke Sr., K.G. Hubbard, K.C. Crawford, M. A. Shafer, and T. Matsui, 2007: An examination of 1997-2007 surface layer temperature trends at two heights in Oklahoma. Geophys. Res. Letts., 34, L24705, doi:10.1029/2007GL031652. [see correction also]
air temperature trends are a function of height above the surface.
Fourth is the complex spatial and temporal heterogeneity of surface air temperatures. The assumption that a single trend value can characterize the heating and cooling of the climate system is based on an oversimplistic assumption based on an object with a uniform mass and temperature change (such as a metal sphere of a few centimeters in size). I discuss this issue in my post
Below are the latest anomaly plots (for February 2011) from http://earthobservatory.nasa.gov/GlobalMaps/view.php?d1=MOD_LSTAD_M&d2=AMSRE_SSTAn_M#