Monthly Archives: November 2005

More on the Limitations of Radiative Forcing as an Indicator of Climate Change

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.

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Filed under Climate Change Forcings & Feedbacks

More Evidence On The Spatial Complexity Of Climate Forcings

A new paper provides more evidence on the complexity of climate forcings. The paper, entitled “Radiative effect of surface albedo change from biomass burning” by Myhre et al. has the following abstract,

“The radiative impact of burn scars from biomass is investigated. Changes in surface albedo derived from satellite observations over the African continent are used as a first order indication of this impact. Because the direct radiative effect of aerosols from biomass burning is dependent on the underlying surface albedo, we investigate the interaction of the direct radiative effect due to biomass burning aerosols with the change in surface reflection due to the burn scars. The radiative effect of reduced surface albedo from burn scars is estimated to be close to 0.1 W m−2 over a region covering the African continent.”

This paper is important, since not only does it show that biomass burning alters the surface albedo, the vertical profile of radiative heating and temperature are changed as a result. The paper also quantifies the magnitude of this effect for Africa where biomass burning is extensive.

Figure 2 of their paper shows significant spatial variations in the annual mean radiative effect which further illustrates that climate forcings often have large spatial heterogeneity that result in heterogeneous spatial trends in weather patterns, as has been discussed on this weblog (see, for example, the weblog of July 28, 2005 What is the Importance to Climate of Heterogeneous Spatial Trends in Tropospheric Temperatures? ).

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Filed under Climate Change Forcings & Feedbacks

Reponse to a November 4, 2005 post on RealClimate

RealClimate posted a comment today on Chaos and Climate.

My response, which I also submitted to RealClimate, is as follows:

James and William- your post, unfortunately, perpetuates the use of climate to refer to long term weather statistics. You state that

“The chaotic nature of atmospheric solutions of the Navier-Stokes equations for fluid flow has great impact on weather forecasting (which we discuss first), but the evidence suggests that it has much less importance for climate prediction.”

This is incorrect.

First, the more appropriate scientific definition of climate is that it is a system involving the oceans, land, atmosphere and continental ice sheets with interfacial fluxes between these components, as we concluded in the 2005 National Research Council report . Observations show chaotic behavior of the climate system on all time scales, including sudden regime transitions, as we documented in Rial, J., R.A. Pielke Sr., M. Beniston, M. Claussen, J. Canadell, P. Cox, H. Held, N. de Noblet-Ducoudre, R. Prinn, J. Reynolds, and J.D. Salas, 2004: Nonlinearities, feedbacks and critical thresholds within the Earth’s climate system. Climatic Change, 65, 11-38.

That the model simulations that you discuss in your weblog do not simulate rapid climate transitions such as we document in our paper illustrates that the models do not skillfully create chaotic behavior over long time periods as clearly occurs in the real world.

That climate is an integrated system and is sensitive to initial conditions is overviewed in Pielke, R.A., 1998: Climate prediction as an initial value problem. Bull. Amer. Meteor. Soc., 79, 2743-2746. Even within the atmospheric portion of the climate system, and applying a simple nonlinear model, based on the work of Lorenz, a chaotic response can be generated which is not evident in the model results you refer to (see Pielke, R.A. and X. Zeng, 1994: Long-term variability of climate. J. Atmos. Sci., 51, 155-159). We show in this study that even short-periodic natural variations of climate forcing can lead to significant long-term variability in the climate system.

We need to move the discussion to studying climate as a complex, nonlinear system which displays chaotic behavior if we are going to provide scientifically robust understanding to policymakers. Readers of your weblog are invited to read my postings at http://www.climatesci.org if they would like to read a different perspective on climate science.

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Filed under Definition of Climate

Revisiting Microclimate Exposure of Surface Air Temperature Monitoring Sites

As a follow-on to the posting of October 31, 2005 on our new paper in Geophysical Research Letters, the paper that was published earlier this year entitled

Davey, C.A., and R.A. Pielke Sr., 2005: Microclimate exposures of surface-based weather stations – implications for the assessment of long-term temperature trends. Bull. Amer. Meteor. Soc., Vol. 86, No. 4, 497–504.

is again listed in this weblog. This paper clearly shows why we need photographic documentation of each surface climate observing site. In response to this study, there has been some limited progress with resources provided to the Colorado Climate Center by the National Climate Data Center (NCDC) to photograph more locations in Colorado (and we will post these photographs as soon as summarized). We also now have photographic documentation of all Global Historical Climate Network (GHCN) sites in Mongolia which will soon be prepared for electronic dissemination.

Such studies show that long-term surface temperature trends have major unresolved issues (see our July 11, 2005 posting The Globally-Averaged Surface Temperature Trend – Incompletely Assessed? Is It Even Relevant?).

To further assess the issue of microclimate exposure, I invite readers of this weblog to submit photographs of GHCN sites using the protocol that is described in the Davey and Pielke paper.

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Filed under Climate Change Metrics

What is Meant by the “Global Surface-Averaged Temperature?”

The AMS Glossary defines “surface temperature” as

“1. In meteorology, the temperature of the air near the surface of the earth; almost invariably determined by a thermometer in an instrument shelter. 2. In oceanography, the temperature of the layer of seawater nearest the atmosphere.”

The term “global-averaged surface temperature” is not defined by the Glossary.

This climate metric is important since it is the basis for so much of the discussion of climate change as discussed in the 2005 National Research Council report (e.g., see the text that begins at http://www.nap.edu/books/0309095069/html/19.html). As stated there,

“The concept of radiative forcing is based on the hypothesis that the change in global annual mean surface temperature is proportional to the imposed global annual mean forcing, independent of the nature of the applied forcing.”

Figure 1-4 of the National Research Council report shows that surface temperature change is central to the climate policy framework.

This temperature, of course, is actually a derived concept based on the global mean radiative forcing. However, in seeking to determine the change of this surface temperature over time, the procedure has been to use surface air and sea surface temperatures to measure this quantity. As shown most recently in our paper, Pielke Sr., and Matsui, 2005: Should light wind and windy nights have the same temperature trends at individual levels even if the boundary layer averaged heat content change is the same?, temperature trends are often a function of height near the surface. Which near surface or surface temperature change, if any of them, should be used? No single level is adequate.

Clearly, the concept of basing climate policy on such an ambiguously measured climate metric as a globally-averaged surface temperature change is inadequate with respect to actual human- and natural-caused climate change. We cannot actually measure such an average directly. Despite its extensive use and long pedigree in the literature and it use in assessments such as in the IPCC reports, a global-averaged surface temperature change based on surface air measurements is not a quantitatively accurate way to communicate climate science to policymakers.

A more appropriate metric for policymakers, for global warming, for instance, would be the global-averaged and regional-averaged patterns of changes in heat content in units of Joules as discussed in the weblogs of September 25th entitled “Is Global Warming Spatially Complex?” and of October 20th “Is Global Warming the Same as Climate Change?.” As recommended in the 2005 National Research Council report, we need to develop new climate metrics to accurately communicate to policymakers and move the science community beyond globally-averaged surface temperature change.

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Filed under Climate Change Metrics