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October-December Issue

Dealing With Global Warming:
The Need for Long-Term Actions

The signing of the Berlin Mandate in 1995 initiated intense international negotiations to develop a response to potential climate change. Under the mandate, diplomats were instructed to devise a set of national ceilings for greenhouse gas emissions for the early years of the next century. To make agreement more likely, developing countries were not to be asked to control emissions, although they account for roughly half the greenhouse emissions now and will emit a larger share in coming decades. The near-term focus is on emissions of carbon dioxide (CO2), recognized as the most important human contributor to potential global warming. Results of the negotiations were the focus of the international conference on climate change that was held in Kyoto, Japan, in December 1997.

As a result of the Berlin Mandate, climate change debate during the past two years has focused on a single question: how much will each of the developed nations promise to cut CO
2 emissions by 2010? Preoccupation with that question worries researchers in the MIT Joint Program on the Science and Policy of Global Change. Achieving near-term limits on CO2 emissions is important, agree Professors Henry D. Jacoby, Ronald G. Prinn, and Richard L. Schmalensee. But negotiations toward that goal may be counterproductive if they delay actions necessary to mount and sustain a broader and longer-term global effort to deal with the threat of potential climate change.

The researchers' concern arises in part from their ongoing investigations into uncertainties that plague predictions of human influences on climate. Experts agree that concentrations of CO
2 and other greenhouse gases in the atmosphere have increased substantially over the past century and that the presence of those gases will tend to trap the sun's infrared energy, raising temperatures at the Earth's surface. But other aspects are controversial. The impact of changes in temperature on our climate depends on complicated, interacting phenomena in the atmosphere, the oceans, and land ecosystems, all of which are poorly understood. Long-term emissions of greenhouse gases are themselves highly uncertain because they depend on economic, technological, and political forces that are hard to predict. And least of all is known about how changes in climate may affect people, society, and natural systems.

To help analyze and quantify the uncertainty associated with climate forecasts, a group of MIT scientists and economists including Professors Jacoby, Prinn, and Schmalensee have formulated a computer model that couples global economic development, climate processes, and ecosystem behavior. Unlike other models in this field, the Integrated Global System Model (IGSM) combines detailed treatments of the relevant natural and economic processes (see e-lab, January-March 1997). Using the model, the researchers have explored the consequences of a range of "reasonable" assumptions about future economic development and fundamental climate processes. Their results provide guidance for both policymaking and future research directions.

One important conclusion is that the range of plausible outcomes is enormous. The figure below shows how using various sets of assumptions about future human activities and about natural processes affects predictions of the change in global average surface temperature between 1990 and 2100. (The predictions assume that future greenhouse gas emissions are not restricted by regulation.) The assumptions are all reasonable, but they produce widely varying results. For example, using the most optimistic assumptions, the predicted increase in temperature by the year 2100 is only 2 degrees F. However, using the "worst-case" assumptions, the predicted increase is fully 9 degrees F. Two thirds of the difference in those predictions is due to uncertainty about climate processes; the other third reflects uncertainty about emissions. The lowest predicted pathway in the figure would probably do little harm, but the highest predicted pathway would almost certainly threaten important natural processes as well as agriculture and other human activities.

Forecasts of Temperature Increase

Clearly, scientists must continue research to improve emissions forecasts, climate models, and impact estimates. In addition, they must continue to watch for evidence that human activities are indeed influencing climate. Many scientists now believe that it may be a decade or more before human effects can be discerned from natural variations in climate. Nevertheless, continued vigilance is critical, as demonstrated in the figure. The shaded region at the bottom represents an estimate of how much global mean temperatures vary naturally during the course of a century. An increase in actual temperatures greater than that natural variability provides evidence that human activities are affecting climate. Looking at the various forecasts, it is clear that the sooner the observed temperatures rise above that range of natural variability, the greater the eventual predicted warming, and the more important it will be to take quick and dramatic action to forestall large climate impacts.

If global warming does turn out to be a problem, IGSM analyses suggest that the emissions reductions agreed to at the Kyoto meeting will not--by themselves--do much to solve it. The researchers considered one of the toughest proposals that was considered at Kyoto: the call by the European Union (EU) to reduce CO
2 emissions from "Annex I" countries to 15% below 1990 levels by 2010--fully 9% more than in the final agreement. (Annex I countries are those subject to emissions limits, namely the members of the Organization for Economic Cooperation and Development as of 1990, plus Eastern Europe and most of the former Soviet Union.) Achieving such a large reduction in CO2 emissions in little more than a decade would be expensive, and maintaining the proposed 2010 level of emissions for the rest of the century would be even more difficult. Yet even under the assumptions of the mid-range MIT forecast in the first figure, IGSM analyses show that this effort by Annex I countries would reduce the projected warming in 2100 by only about 20%, largely because of projected emissions growth in developing countries--growth that is not restricted by the Kyoto agreement. If climate change turns out to be a serious threat, this response would be inadequate; if it turns out not to be a threat, it would be a large-scale waste of resources.

A longer-term goal involves stabilizing atmospheric concentrations of greenhouse gases. The EU and others have recommended stabilizing concentrations of CO
2 at 550 ppm (roughly twice pre-industrial levels), and the Intergovernmental Panel on Climate Change (IPCC) has outlined an emissions-reduction strategy for achieving that goal. Based on an IGSM analysis, the MIT researchers predict that following that strategy would lower the mid-range warming forecast by only about 30% in 2100. Moreover, the Annex I nations could not accomplish the called-for emissions reductions by themselves. The figure below shows the maximum Annex I emissions consistent with the EU's proposed target (based on assumptions corresponding to the mid-range of the forecasts in the figure above). The non-Annex I nations are assumed to continue emitting CO2 without restriction, and their forecasted emissions are simply subtracted from the global total that the EU proposal allows, as calculated by the IPCC. Without participation by the developing world, following the proposed emissions-reduction strategy would require that emissions by the Annex I nations somehow become negative around the middle of the next century!

Allowed Carbon Emissions from Developed Nations Under Proposed Plan to Stabilize Atmospheric Carbon Dioxide

One conclusion seems clear: unless scientists discover soon that greenhouse warming is definitely not a threat, the struggle to devise a global response will occupy not just our generation but future generations as well. The MIT researchers identify three actions that should be taken now to help future generations cope. The first is to develop better technical options that could, if necessary, permit us to control greenhouse gas emissions while maintaining economic growth. A serious attempt to produce important new technological options would be cheap relative to the cost of controlling emissions resulting from the use of current technologies. The best route to achieving such advances is not clear. Marketplace incentives appear important for stimulating private sector R&D, while public expenditure may be needed on basic research and fundamental technologies. The latter will require a major turnabout of today's minimal commitment to developing greenhouse-friendly technology.

The second action is to begin developing institutions and policies that allow us to mount and sustain a very long term global effort to control climate change. We need to establish an institutional structure for managing global emissions agreements that can evolve easily over time. Useful insights can be gained from the international trade regime developed under the General Agreement on Tariffs and Trade (GATT), now the World Trade Organization. This organization has grown and evolved over time, adding countries and goods along the way, peacefully resolving substantial conflicts in national economic interests, and contributing to global economic growth. (Unfortunately, achieving that success required fifty years of hard work.) In addition, policies limiting CO
2 emissions should be just one part of a larger, carefully designed set of international agreements that address all the issues involved. For example, agreements must cover not just CO2 produced from fossil fuels but also all the important sources and sinks of significant greenhouse gases. They also need to provide for reliable emissions monitoring and for some system of sanctions for those who violate their obligations.

The third area that warrants attention concerns the inclusion of non-Annex I nations. Making significant reductions in global emissions will require global participation. Therefore, Annex I targets and timetables must be designed to facilitate the inclusion of non-Annex I nations. In many cases, these nations will not be able to afford voluntary abatement much before the end of the next century. Thus, if the rich countries want to stabilize greenhouse gas concentrations, they must not only control their own emissions but also pay poor countries to reduce their emissions. Rough estimates of the costs that would be involved imply international transfers of wealth on a scale well beyond anything in recorded history. We need to create an international system that can transfer substantial sums to developing countries to support their participation in an emissions-control effort.

Including the developing countries in that effort will affect another important financial factor: the global cost of controlling emissions. Many of the cheapest emissions-abatement opportunities are in developing countries, and exploiting those opportunities first would minimize the global cost of achieving a given reduction in emissions. To take advantage of those opportunities, some observers have proposed establishing a system of emissions trading--the approach that has dramatically reduced sulfur dioxide pollution in the United States (see e-lab, January-March 1997). Emissions trading is not included in the Kyoto agreement. But even if it is adopted in later agreements, it will work effectively only if all countries have agreed to emissions limits. If the developing countries do not participate, the advantages of trading are drastically reduced.

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Last updated: 01/25/98

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