Gavin Schmidt in his Comment #1 on November 21 2006 introduced a link to very useful data that has been analyzed from the GISS model. The analyses are available under the heading “Datasets and Images – Efficacy of Climate Forcings”“.
Their summary illustrates the spatial structure of the climate forcings from their model simulations. The forcing Fa [“âFaâ, the adjusted forcing, is the flux change at the top of the atmosphere (and throughout the stratosphere) after the stratosphere is allowed to adjust radiatively to the presence of the forcing agentâ?], can be used to illustrate the need to incorporate the spatial structure of climate forcings in any assessment of the role of humans in altering the climate system.
Spatial maps of Fa from the GISS model include, for example, the forcings due to:
1. 2 X CO2
A critically important research question is
How important is the spatial gradient of the diabatic heating and cooling from such climate forcings on climate patterns including atmospheric and ocean circulations?
In the paper
Matsui, T., and R.A. Pielke Sr., 2006: Measurement-based estimation of the spatial gradient of aerosol radiative forcing. Geophys. Res. Letts., 33, L11813, doi:10.1029/2006GL025974
we proposed a metric to assess the relative importance of different climate forcings. We concluded that
“This paper diagnoses the spatial mean and the spatial gradient of the aerosol radiative forcing in comparison with those of well-mixed green-house gases (GHG). Unlike GHG, aerosols have much greater spatial heterogeneity in their radiative forcing. The heterogeneous diabatic heating can modulate the gradient in horizontal pressure field and atmospheric circulations, thus altering the regional climate. For this, we diagnose the Normalized Gradient of Radiative Forcing (NGoRF), as a fraction of the present global heterogeneous insolation attributed to human activity.”
Figure 1 in the Matsui and Pielke article presents a spatial map of shortwave aerosol direct radiative forcing in the atmosphere equatorward of 37 degrees, with Figure 5 comparing the aerosol forcings to that of the GHG in this latitude band.
The GISS analyses can and should be analyzed using this diagnostic metric of climate change.
An important conclusion with respect to the evidence of such significant spatial structure in the diabatic heating from human climate forcings is that the IPCC assessment needs to include this climate system analysis. Such an approach, as presented in the Matsui and Pielke paper, was recommended by the 2005 National Research Council Report “Radiative Forcing of Climate Change: Expanding the Concept and Addressing Uncertainties“.
We look forward to seeing the IPCC discussion of relative importance of the spatial structure of climate forcings. They would be derelict in their responsibility to present the spectrum of information on climate change if they do not include this analysis in their upcoming report.