Further Confirmation Of The Inadequacies Of A Global Average Radiative Forcing To Monitor Climate Change

In the 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

it is written

“Despite all these advantages, the traditional global mean TOA 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. A new metric to account for the vertical structure of radiative forcing is recommended below.”

and

“Although the traditional TOA radiative forcing concept remains very useful, it is limited in several ways. It is inadequate to describe fully the radiative effects of several anthropogenic influences including

  • absorbing aerosols, which lead to a positive radiative forcing of the troposphere with little net radiative effect at the top of the atmosphere;
  • effects of aerosols on cloud properties (including cloud fraction, cloud microphysical parameters, and precipitation efficiency), which may modify the hydrological cycle without significant radiative impacts;
  • perturbations of ozone in the upper troposphere and lower stratosphere, which challenge the manner in which the stratospheric temperature adjustment is done; and
  • surface modification due to deforestation, urbanization, and agricultural practices and surface biogeochemical effects.”

Unfortunately, the 2007 IPCC  inadequately considered this perspective that was presented in the 2005 NRC study.

There is a new article, however, that reaffirms the NRC conclusion and recommendations. It is

Don Wuebbles, Piers Forster, Helen Rogers, Redina Herman, 2010: Issues and Uncertainties Affecting Metrics for Aviation Impacts on Climate. Bulletin of the American Meteorological Society. Volume 91, Issue 4 (April 2010).

While the paper is specifically with respect to aircraft contrails, their findings and recommendations apply to all heterogeneous climate forcings. The article has a very effective summary table on page 494 that is titled “A comparison of the metrics and modeling tools that can be used for the evaluation of aviation’s climate impact”.

Extracts from this table list the disadvantages of several climate metrics including radiative forcing where it is reported that

“Without modification (efficacy factors) it does not account for differences in climate response between forcings (see Fuglestvedt et al. 2003; Berntsen et al. 2005); it is far removed from eventual climate impact; and it does not adequately account for regional variations of the climate effect.”

With respect to global warming potential, they write

“Far removed from climate impact and without modification, it does not account for differences in climate response; changing background atmosphere is not taken into account; does not account for regional variation in impact.”

This study illustrates the continued awakening by the climate research community of the diverse range of influences of humans within the climate system that we presented in our paper

Pielke Sr., R., K. Beven, G. Brasseur, J. Calvert, M. Chahine, R. Dickerson, D. Entekhabi, E. Foufoula-Georgiou, H. Gupta, V. Gupta, W. Krajewski, E. Philip Krider, W. K.M. Lau, J. McDonnell,  W. Rossow,  J. Schaake, J. Smith, S. Sorooshian,  and E. Wood, 2009: Climate change: The need to consider human forcings besides greenhouse gases. Eos, Vol. 90, No. 45, 10 November 2009, 413. Copyright (2009) American Geophysical Union,

as well as further evidence that the 2007 IPCC report failed to adequately consider the role of all of the first order human climate forcings.

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