Further Evidence On The Breadth Of The Role Of Humans With Respect To Climate Change

On Friday October 30 2009 my son posted “Roger Pielke Sr. is Sure Going to Like This

He is correct!  There is an growing acceptance that the first order human climate forcings are more diverse than was communicated in the 2007 IPCC report.

The new papers that he mentions in his post include

Drew T. Shindell, Greg Faluvegi, Dorothy M. Koch, Gavin A. Schmidt, Nadine Unger, Susanne E. Bauer, 2009: Improved Attribution of Climate Forcing to Emissions.  Science 30 October 2009: Vol. 326. no. 5953, pp. 716 – 718 DOI: 10.1126/science.1174760

in which the abstract reads

“Evaluating multicomponent climate change mitigation strategies requires knowledge of the diverse direct and indirect effects of emissions. Methane, ozone, and aerosols are linked through atmospheric chemistry so that emissions of a single pollutant can affect several species. We calculated atmospheric composition changes, historical radiative forcing, and forcing per unit of emission due to aerosol and tropospheric ozone precursor emissions in a coupled composition climate model. We found that gas-aerosol interactions substantially alter the relative importance of the various emissions. In particular, methane emissions have a larger impact than that used in current carbon-trading schemes or in the Kyoto Protocol. Thus, assessments of multigas mitigation policies, as well as any separate efforts to mitigate warming from short-lived pollutants, should include gas-aerosol interactions.”

A second paper is

Arneth, Almut , Nadine Unger, Markku Kulmala, Meinrat O. Andreae, 2009: Clean the Air, Heat the Planet? Science 30 October 2009: Vol. 326. no. 5953, pp. 672 – 673 DOI: 10.1126/science.1181568

Text from this paper includes

“The push toward cleaner air in Beijing before the 2008 Olympic Games was a vivid reminder of the need to control air pollution, not only in Asia but in many regions of the world …. There is mounting evidence for particle- and ozone-related health effects …. Furthermore, ozone and aerosol particles affect Earth’s radiation balance …: Many aerosols cool the atmosphere (a negative forcing), whereas ozone and black carbon aerosol have a warming effect (a positive forcing). There is thus a strong motivation for treating air pollution control and climate change in common policy frameworks … However, recent model studies … have shown that changes in pollutant and precursor emissions, atmospheric burden, and radiative forcing are not necessarily proportional. Furthermore, as Shindell et al. report on page 716 of this issue, current models do not capture many of the complex atmospheric processes involving aerosols and reactive trace gases.”


“How will the geographically inhomogeneous changes in emissions translate into the metric that dominates the political debate— the global and local surface temperature?”

“Direct and indirect interactions between climate change, land ecosystems, and chemistry can amplify or dampen the climate effects of air pollutants, but are poorly represented in models……..Furthermore, land use and land cover change may alter biogenic and pyrogenic emissions of short-lived species as strongly as, if not more than, climate change. These interactions are increasingly being studied …..but are not yet well understood…”

The need for a broader view was summarized in

National Research Council (NRC), 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.

In the Executive Summary of this NRC (2005) report, excerpts read

“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. These effects can be addressed by considering surface as well as TOA radiative forcing as a metric of energy imbalance. The net radiative forcing of the atmosphere can be deduced from the difference between TOA and surface radiative forcing and may be able to provide information on expected changes in precipitation and vertical mixing. Adoption of surface radiative forcing as a new metric will require research to test the ability of climate models to reproduce the observed vertical distribution of forcing (e.g., from aircraft campaigns) and to investigate the response of climate to the vertical structure of the radiative forcing.”

“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. Improving societally relevant projections of regional climate impacts will require a better understanding of the magnitudes of regional forcings and the associated climate responses.”

“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. No metrics for quantifying such nonradiative nonradiative “>forcings have been accepted. Nonradiative forcings have eventual radiative impacts, so one option would be to quantify these radiative impacts. However, this approach may not convey appropriately the impacts of nonradiative forcings on societally relevant climate variables such as precipitation or ecosystem function. Any new metrics must also be able to characterize the regional structure in nonradiative forcing and climate response.”

The new Shindell et al 2009 and  Arneth et al 2009 papers, while still too narrowly focused on global average radiative forcing as the appropriate metric to diagnose climate change, nevertheless,  support the NRC (2005) findings that global climate syatem heat changes involve much more than just  “a buildup of greenhouse gases in the atmosphere from the burning of fossil fuels“.

The authors of the Shindell et al and  Arneth et al papers are starting to move in the direction of a broader viewpoint of how humans are affecting the climate system. They still need to reject, however,  the scientifically (and policy) inadequate focus on “the global and local surface temperature” as “the metric that dominates the political debate” .

The human role in the climate system needs to be also assessed using the resource-based, bottom-up approach that is discussed, for instance, in our paper

 Pielke Sr., R.A., J.O. Adegoke, T.N. Chase, C.H. Marshall, T. Matsui, and D. Niyogi, 2007: A new paradigm for assessing the role of agriculture in the climate system and in climate change. Agric. Forest Meteor., Special Issue, 132, 234-254

and in my post

Further Comments On The Vulnerability Perspective

As my son discussed, “Once reconceptualized, climate policy can proceed upon multiple, parallel tracks, and thus have a greater chance to keep in step with evolving science and actually have a chance to make progress with respect to policy goals”.  The use of the vulernability framework, summarized below, can assist in this reconceptualization.

The Vulnerability Framework

There are 5 broad areas that we can use to define the need for vulnerability assessments : water, food, energy, health and ecosystem function. Each area has societally critical resources. The vulnerability concept requires the determination of the major threats to these resources from climate, but also from other social and environmental issues. After these threats are identified for each resource, then the relative risk from natural- and human-caused climate change (estimated from the GCM projections, but also the historical, paleo-record and worst case sequences of events) can be compared with other risks in order to adopt the optimal mitigation/adaptation strategy.

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