The question the scientists, bloggers and media are asking is what is the magnitude of a so-called “climate sensitivity” to the human input of CO2 and a few other greenhouse gases? The more appropriate question, is why do we care?
What they are calling “climate sensitivity” is in fact the resultant change in the global average surface temperature anomaly to a change in the global average radiative forcing (e.g. see). Climate is so much more than this, as is documented in the figure below from NRC (2005) which I have presented on my weblog numerous times before.
The problem with focusing on the use of a so-called “climate sensitivity” as the holy grail of climate to communicate to policymakers is that it has essentially frozen the adoption of effective adaptation and mitigation responses to the real climate issues.
The real climate issues should be on how climate variability and longer term climate change (from both human and natural forcings) affect risks to our key resources of water, food, energy, human health and ecosystem function. The narrow definition of the so-called “climate sensitivity”, while of interest as a science question, is essentially worthless as a metric to use in order to reduce the threats faced by these key resources.
Instead of the vitriolic debates on weblogs and media on the Spencer and Braswell (2011) and Dessler (2011) papers, lets move towards a bottom-up, resource-based perspective such as we have proposed in our paper
Pielke Sr., R.A., R. Wilby, D. Niyogi, F. Hossain, K. Dairuku, J. Adegoke, G. Kallos, T. Seastedt, and K. Suding, 2011: Dealing with complexity and extreme events using a bottom-up, resource-based vulnerability perspective. AGU Monograph on Complexity and Extreme Events in Geosciences, in press.
The bottom line conclusion is that the assessment of risks to key resources, including threats from climate variability and climate change, based on the magnitude of a so-called “climate sensitivity“, is a fatally flawed framework for developing effective adaptation and mitigation policies to reduce those risks.
The reduction of risks using the bottom-up, resource-based framework, in contrast, is a much more valuable and inclusive approach. With this perspective policymakers can adopt effective mitigation and adaptation methodologies to deal with the diversity of complex threats to society and the environment that will occur in the coming decades, regardless of the extent that humans are altering the global average surface temperature.