Missed Opportunity By The IPCC

The International Panel on Climate Change (IPCC) released its 2007 Statement for Policymakers this month (see) However, rather than broadening out the assessment of the human role within the climate system, the report continues to focus narrowly on the global-average radiative forcing to discuss the role of human climate forcings (e.g. see Figure SPM-2 on page 4 of the IPCC Report)..

 This is not only misleading for policymakers and the public, but is scientifically flawed (see also).

 The need to broaden the assessment of human and natural climate forcings was clearly articulated in the 2005 National Research Council Report

 National Research Council, 2005: Radiative forcing of climate change: Expanding the concept and addressing uncertainties. Committee on Radiative Forcing Effects on Climate Change, Climate Research Committee, Board on Atmospheric Sciences and Climate, Division on Earth and Life Studies, The National Academies Press, Washington, D.C., 208 pp.

 Where key findings included the statements that,

“……the traditional global mean TOA [Top of the Atmosphere] radiative forcing concept has some important limitations, which have come increasingly to light over the past decade. The concept is inadequate for some forcing agents, such as absorbing aerosols and land-use changes,  that may have regional climate impacts much greater than would be predicted from TOA radiative forcing. Also, it diagnoses only one measure of climate change—global mean surface temperature response—while offering little information on regional climate change or precipitation. These limitations can be addressed by expanding the radiative forcing concept and through the introduction of additional forcing metrics. In particular, the concept needs to be extended to account for (1) the vertical structure of radiative forcing, (2) regional variability in radiative forcing, and (3) nonradiative forcing.”

The Executive Summary of the Report states with respect to the need to account for the vertical structure of the radiative forcings,

“The relationship between TOA radiative forcing and surface temperature is affected by the vertical distribution of radiative forcing within the atmosphere. This effect is dramatic for absorbing aerosols such as black carbon, which may have little TOA forcing but greatly reduce solar radiation reaching the surface. It can also be important for land-use driven changes in the evapotranspiration flux at the surface, which change the energy deposited in the atmosphere without necessarily affecting the surface radiative flux...”

The Executive Summary of the Report states with respect to the need to account for the regional variations of the radiative forcings,

 “Regional variations in radiative forcing may have important regional and global climatic implications that are not resolved by the concept of global mean radiative forcing. Tropospheric aerosols and landscape changes have particularly heterogeneous forcings. To date, there have been only limited studies of regional radiative forcing and response. Indeed, it is not clear how best to diagnose a regional forcing and response in the observational record; regional forcings can lead to global climate responses, while global forcings can be associated with regional climate responses. Regional diabatic heating can also cause atmospheric teleconnections that influence regional climate thousands of kilometers away from the point of forcing….”

The Executive Summary of the Report states with respect to the need to account for the importance of non-radiative forcings,

 “Several types of forcings—most notably aerosols, land-use and land-cover change, and modifications to biogeochemistry—impact the climate system in nonradiative ways, in particular by modifying the hydrological cycle and vegetation dynamics. Aerosols exert a forcing on the hydrological cycle by modifying cloud condensation nuclei, ice nuclei, precipitation efficiency, and the ratio between solar direct and diffuse radiation received. Other nonradiative forcings modify the biological components of the climate system by changing the fluxes of trace gases and heat between vegetation, soils, and the atmosphere and by modifying the amount and types of vegetation.”

The failure of the IPCC Report to broaden their perspective reinforces the conclusion that this document is intended to provide support for energy policy changes, rather than a comprehensive assessment of the role of humans within the climate system (e.g. see). This also explains the outcries for major immediate energy policy changes in order to prevent catastrophic climate change in the next few years, if, as is likely, the real world climate observations deviate significantly from the model predictions.