26 October 2009

How Much Future Hurricane Damage Can Stopping Global Warming Achieve?

In the Huffington Post Senator Barbara Boxer (D-CA) makes a familiar argument:
Whether or not it was caused or worsened by climate change, the devastating effects of Hurricane Katrina provide a window into the kind of world we can expect if global warming continues unabated.

Earlier this month, President Obama visited New Orleans. In 2005, Hurricane Katrina took an estimated 1,700 lives and displaced 1 million people. The total cost of the storm is estimated at well over $100 billion, with some estimates much higher. Four years later, the people of the region are still suffering, and it will take billions more to rebuild the Gulf Coast and protect coastal communities from future storms. And that's just what one storm cost us. How many of these disasters can we withstand? We must take action to address these real and costly threats. . .

Comprehensive clean energy legislation like the Clean Energy Jobs and American Power Act that Senator Kerry and I have introduced in the Senate is not only the right choice to transform our economy, create jobs, and make America more secure. It is also our most effective insurance policy against a dangerous future.
In a 2007 paper (peer-reviewed, and subsequently replicated/confirmed) I looked at the relative roles of climate change and societal change on future tropical cyclone losses. In the paper I simply assumed a very large anthropogenic climate change effect of a 36% increase in the intensity of every storm from what it would have been otherwise. I also assumed that efforts to reduce emissions have an instantaneous and proportional effect on storm intensity. No one in the scientific community that I am aware of believes either of these assumptions to be the case in the real world, so I have clearly erred on the side of overstating both the magnitude of potential changes in storm intensity and the efficacy of emissions reductions to reduce that intensity.
Pielke, Jr., R. A., 2007. Future Economic Damage from Tropical Cyclones: Sensitivities to Societal and Climate Changes, Philosophical Transactions of the Royal Society, Vol. 365, No. 1860, pp. 1-13.
Here is what I found in the paper:
. . . the analysis in this paper, consistent with that in earlier studies, suggests that any practically or politically conceivable energy policies can have at best a very small and perhaps imperceptible effect on future tropical cyclone damage. Consequently, policy action should focus on reducing vulnerabilities, at least in the short term. This finding should not diminish the importance of mitigation policies in response to climate change, but can help to better align political advocacy with potential policy effectiveness.
It is misleading, at best, to sell emissions reduction policies on the basis of their potential "to address these real and costly threats" and to assert that "clean energy legislation" now being considered in the U.S. Congress "is also our most effective insurance policy against a dangerous future."

To be absolutely clear, here is what my paper concluded:
To emphasize, the analysis presented here should not be interpreted as an argument against mitigation of greenhouse gases. And there is no suggestion here that human-caused climate change is not real or should not be of concern. Instead, this simple analysis under the most favourable assumptions for mitigation indicates that in the coming decades any realistically achievable mitigation policies can have at best only a very small and perhaps imperceptible effect on global tropical cyclone damage, whatever the costs of those policies might happen to be. This reality explains why adaptation necessarily must be at the centre of climate policy discussions and viewed as a complement to mitigation policies. It also helps to explain why mitigation policies in the short term necessarily must be focused on their non-climate benefits.

Most importantly, these results show how misleading it is to use tropical cyclone damage as a reason for greenhouse gas mitigation when other actions have far more potential effectiveness. The images of storm-spawned death and destruction are no doubt compelling, but it is misleading or disingenuous to suggest that energy policies can have an appreciable effect on future damages. The only way to arrive at tropical cyclone damages that exceed the societal factors is to hold societal change constant and focus only on the climate component, which is in fact what some studies have done in the past.12 Climate change is an important issue and policy action on mitigation makes sense, but when compared with available alternatives for addressing the escalating costs of tropical cyclones, ameliorating damage from tropical cyclones should not be conflated with other justifications for changing energy policies. Those interested in honest advocacy and effective policy should keep these issues separate.
The fact that reducing emissions will do little to address the growing toll of disasters is an example of what my colleague Steve Rayner from Oxford calls "uncomfortable knowledge." This is especially the case for those who continue to misjustify policies that are better justified for other reasons. In the long run climate policy will be better served by making honest arguments. A step in that direction would be to stop the pattern of using the specter of future Hurricane Katrinas (and disasters like it) as a basis for changing energy policies.