A climate-change study by researchers from MIT and the Marine Biological Laboratory at Woods Hole shows that a strategy for controlling multiple gases associated with greenhouse warming could reduce control costs by more than 60 percent compared with controlling carbon dioxide (CO2) alone.
This first comprehensive assessment of economic, atmospheric, climatic and ecosystem effects of the Kyoto Protocol on Climate Change hit newsstands in the October 7 issue of Nature.
The study also indicates flaws in the "yardstick" by which gases are compared under the Kyoto Protocol, an agreement now signed by 84 countries including the United States that was negotiated in December 1997 with the intent of slowing global warming.
"The main finding is that including gases other than CO2 emissions from fossil fuels could greatly reduce costs of meeting the [Kyoto] Protocol," observed Dr. John Reilly, lead author of the paper and associate director for research at the MIT Joint Program on the Science and Policy of Global Change. "Economically efficient policies will be required that encourage reduction of these emissions -- not an easy task, as reductions must come from sources as diverse as landfills, aluminum production, livestock and electrical switchgear."
Added co-author Professor Ronald Prinn, head of the Department of Earth, Atmospheric, and Planetary Sciences and co-director of the Joint Program, "No other effort to date has comprehensively considered both the scientific and economic implications of the Protocol. The results are exciting and illuminating."
Much current analysis and policy discussion narrows climate issues to a debate about carbon emissions from fossil fuels. Most economic analyses likewise have considered only emissions of CO2 from fossil fuels. This situation has, according to the present study, led to an approximately 21 percent overestimation of annual costs in 2010 for meeting Kyoto Protocol emissions caps in industrialized regions.
In contrast, the present study analyzes climate policy as negotiated under the Kyoto agreement, including critical issues like forest "sinks" (repositories of CO2 absorbed from the atmosphere) and non-CO2 greenhouse gases. It also explicitly considers atmospheric interactions among these gases, climate feedbacks, the roles of carbon monoxide and nitrogen oxides (key components of smog), and aerosols' cooling effect.
Significantly for climate and ecosystems, the study shows that inclusion of non-CO2 gases in the Kyoto Protocol leads to greater reductions in the impact of greenhouse gas emissions than if only CO2 had been included. Achieving approximately the same reduction in warming by controlling only fossil CO2 could cost more than 60 percent more than an effort controlling other gases as well. Failure to consider non-CO2 greenhouse gases and sinks also has differential regional effects that could affect the pattern of emissions trading.
The Nature study also notes flaws in the yardstick used to compare greenhouse gases under the Kyoto Protocol. The protocol, which has not yet been ratified by the number of countries needed before it can enter into force, calls for reductions in emissions of several radiative (Earth-warming) gases to be credited against a CO2-equivalent emissions "cap." This cap is calculated in terms of Global Warming Potential (GWP), an index defining the contribution of each greenhouse gas to atmospheric warming relative to CO2.
The Nature article shows, however, that use of GWPs as applied in the Kyoto Protocol mitigates climate change considerably more for multi-gas strategies than for supposedly equivalent CO2-only control when emissions cuts are deep enough to stabilize the radiative effects of these gases.
"This result indicates significant weakness in the whole GWP approach, in that this approach does not 'level the playing field' for all possible strategies. Instead, an integrated systems approach appears necessary," said Professor Prinn.
In fact, predictions based on the present study (which employs an integrated global systems model) indicate that when Kyoto-specified GWPs are used, the choice of control strategy could determine whether or not the radiative effects of all gases are stabilized. Differences in effects between strategies would develop early in the 21st century, soon after the point at which the researchers hypothesized that the Protocol will be extended to include developing countries, in which emissions of non-CO2 greenhouse gases are substantial.
While many uncertainties remain in forecast efforts of this type, the bottom line of this study is that taking non-CO2 gases into account could contribute substantially to the mitigation of climate change.
Additional authors of the Nature paper are: Dr. Jochen Harnisch, a postdoctoral fellow with the Joint Program at the time of the study; Jean Fitzmaurice, research associate with the Joint Program during the study; Professor Henry Jacoby of the Sloan School and co-director of the Joint Program; David Kicklighter, senior research assistant; Dr. Jerry Melillo, co-director of the Ecosystems Center at the Marine Biological Laboratory, Woods Hole; Peter Stone, professor of climate dynamics and director of the Climate Modeling Initiative; and Drs. Andrei Sokolov and Chien Wang, research scientists in the Joint Program.
This research was funded by the Joint Program on the Science and Policy of Global Change.������
A version of this article appeared in MIT Tech Talk on October 27, 1999.
