Comment The Royal Society Report “On Climate Change: A Summary Of The Science”

The Royal Society has presented a new summary of their perspective on climate science in

Climate change: A Summary of the Science

This report is an addition to the literature on this subject. However, the report perpetuates the significant misconception that global warming and climate change are synonymous. They are NOT.

Their text

“Climate forcing (also known as radiative forcing) [is the] imbalance in the Earth’s energy budget resulting from, for example, changes in the energy received from the Sun, changes in the amounts or characteristics of greenhouse gases and particles, or changes in the nature of the Earth’s surface”

and

“Climate sensitivity…is the amount of climate change (as measured by the change in globally-averaged surface temperature) for a given amount of climate forcing.”

is not scientifically accurate. Radiative forcing is just a subset of a diversity of climate forcings. Climate sensitivity is much more than can be diagnosed by a change in the globally-averaged surface temperature.

The Royal Society has ignored this broader view. For example, the US 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

includes the text

“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……”

“Climate is conventionally defined as the long-term statistics of the weather (e.g., temperature, cloudiness, precipitation). This definition emphasizes the atmospheric and physical components of the climate system. These physical processes within the atmosphere are affected by ocean circulation, the reflectivity of the Earth.s surface, the chemical composition of the atmosphere, and vegetation patterns, among other factors. Improved understanding of how the atmosphere interacts with the oceans, the cryosphere (ice-covered regions of the world), and the terrestrial and marine biospheres has led scientists to expand the definition of climate to encompass the oceanic and terrestrial spheres as well as chemical components of the atmosphere (Figure 1-1). This expanded definition promotes an Earth system approach to studying how and why climate changes.”

and

“Global radiative forcing at the top of the atmosphere (TOA), as used in assessments by the Intergovernmental Panel on Climate Change (IPCC), is relatively easy to compute in climate models and has straightforward policy applications. However, it has important limitations when applied to radiative forcing agents not conventionally considered as such (e.g., aerosols, land-use change) or when used to measure climatic implications other than global mean temperature (e.g., regional precipitation). To address these limitations, the concept of radiative forcing needs to be expanded; that expansion is a major theme of this report.”

This perspective was not included adequately in the 2007 IPCC report nor in the Royal Society report.

A short summary of this broader perspective is 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

where we wrote

“In addition to greenhouse gas emissions, other first-order human climate forcings are important to understanding the future behavior of Earth’s climate. These forcings are spatially heterogeneous and include the effect of aerosols on clouds and associated precipitation [e.g., Rosenfeld et al., 2008], the influence of aerosol deposition (e.g., black carbon (soot) [Flanner et al. 2007] and reactive nitrogen [Galloway et al., 2004]), and the role of changes in land use/land cover [e.g., Takata et al., 2009]. Among their effects is their role in altering atmospheric and ocean circulation features away from what they would be in the natural climate system [NRC, 2005]. As with CO2, the lengths of time that they affect the climate are estimated to be on multidecadal time scales and longer.”

The Royal Society is making progress, but it still has more work to do in order to properly report on the current understanding of the role of humans and natural processes within the climate system.

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