As discussed on this weblog (e.g., see the August 1, 2005 posting Is There a Human Effect on the Climate System? ) and documented in the 2005 National Research Council Report , we need to move beyond global radiative forcing as the primary metric to define climate change. A new paper provides additional support for this view.
The paper in Climate Dynamics by Stuber et al. entitled “Why radiative forcing might fail as a predictor of climate change” (subscription required). Their paper states,
“A series of climate model simulations involving ozone changes of different spatial structure reveals that the climate sensitivity parameter λ is highly variable: for an ozone increase in the northern hemisphere lower stratosphere, it is more than twice as large as for a homogeneous CO2 perturbation. A global ozone perturbation in the upper troposphere, however, causes a significantly smaller surface temperature response than CO2. The variability of the climate sensitivity parameter is shown to be mostly due to the varying strength of the stratospheric water vapour feedback.”
The climate sensitivity parameter λ is defined by the equation ΔTsurf = λ times RF where RF is the radiative forcing. The term ΔTsurf is the global mean surface temperature and RF is the global mean radiative forcing. This paper further shows the inadequacies of using the concept of a climate sensitivity, as defined by λ, as well as the overly simplistic concept of a global averaged surface temperature and a global mean radiative forcing (e.g., see the weblog of September 25, 2005 Is Global Warming Spatially Complex? and July 28th What is the Importance to Climate of Heterogeneous Spatial Trends in Tropospheric Temperatures?). The climate system is much more complex and spatially heterogeneous than represented by this simple relationship. The IPCC and other climate assessments need to move beyond a narrow perspective of the climate system.