Control of sulfur and carbon emissions

David Bradford has been involved with two projects involving the economic of impacts of controlling gases other than CO2. In one study, Bradford and colleagues studied the outcome of including both health and climate damages related to sulfate aerosols in the DICE model. Reducing fossil fuel combustion to limit the health damages of sulfur emissions simultaneously reduces carbon emissions, but also acts to warm the atmosphere due to a decline in sulfate aerosols in the atmosphere.

The authors carried out multiple simulations designed to quantify the economic and climate impacts of sulfur emission control. They found that in a scenario that takes both health and climate damages into account, economically optimal carbon emissions decrease by ~16% relative to a scenario considering climate damages alone. The accompanying decrease in sulfur aerosols leads to a net warming of the climate by about 0.2 ºC in the short-term. In the long-term, however, the lower carbon emissions lead to lower temperatures than in a business-as-usual scenario, making a health-based strategy a promising motivator for early action on CO2 emissions control.


Ozone production and NOx controls

In a second paper, Bradford and colleagues combined an atmospheric model with economic and demographic information to estimate health damage costs from ozone formation due to nitrogen oxide emissions from large point sources. Using a regional atmospheric model of the eastern United States, the group examined how the amount of ozone produced from a fixed quantity of nitrogen oxides emitted from power plants varied depending on temperature variations and local biogenic hydrocarbon emissions. The results indicate that for the same NOx emission, ozone produced can vary by more than a factor of three. In addition, the simulations show that the variation in health damages caused by ozone depends strongly on the size of the exposed population. Combining both effects results in a factor of six difference in resulting mortalities for identical quantities of NOx emitted.

The work has implications for the emission cap-and-trade approach that has been successful in reducing total NOx emissions from large point sources. Because it does not control for the location or time during the summer that emissions take place, nor for the resulting damages, it is less successful at minimizing the damages that result from emissions permitted under the cap. The group’s simulations indicate that total damage might be more effectively reduced by providing incentives to reduce NOx emissions at times and in locations where health damages are greatest.


Policy Implications of Uncertain Climate Thresholds and Learning

Klaus Keller’s work over the past year has focused on analyzing the effects of uncertain climate thresholds and learning on economically efficient climate policies. Many optimal economic growth models suggest that uncertain climate damages justify only low levels of near-term CO2 abatement. However, these models have neglected the effects of potential climate thresholds, such as a widespread coral bleaching, a disintegration of the West Antarctic Ice Sheet, or a shutdown of the North Atlantic thermohaline circulation.

Keller and colleagues used economic optimal growth models to demonstrate that uncertain climate thresholds affect the choice of risk-management strategies considerably. Specifically, reducing the risk of a widespread coral bleaching implies drastic reductions in greenhouse gas emissions within decades. Virtually unchecked greenhouse gas emissions to date (combined with the inertia of the coupled natural and human systems) may have already committed future societies to a widespread demise of coral reefs. Their results show that strategies to reduce the risk of a West Antarctic ice sheet disintegration allow for a smoother decarbonization of the economy within a century and may well increase consumption in the long run (due to the concomitant reduction in other climate change impacts such as sea-level rise).

Keller will continue to expand his study of decision-making under uncertainty as a Co-Principal Investigator at a new NSF funded project. The project will center on fundamental research into two key questions relevant to climate change decision-making: (1) What are the best ways to represent uncertainty for decision-makers and (2) What tools and methods work best in practice in providing these representations to decisionmakers? Specifically, Dr. Keller will lead a project to analyze the design of scientific observation systems that could provide actionable warning of abrupt climate change.