In its analysis, the panel that wrote Limiting the Magnitude focused on a range of global atmospheric GHG concentrations between 450 and 550 ppm CO₂-eq. The resulting budget range corresponds roughly to a reduction of emissions from 1990 levels by 80 to 50 percent, respectively. This budget range is based on “global least cost” economic efficiency criteria for allocating global emissions among countries, the panel noted.

...meeting an emissions budget in the range suggested above, especially the more stringent budget of 170 GtCO₂-eq, will require a major departure from business-as-usual emission trends (in which US emissions have been rising at a rate of ~one percent per year for the past three decades). The main drivers of GHG emissions are population growth and economic activity, coupled with energy use per capita and per unit of economic output (“energy intensity”). Although the energy intensity of the US economy has been improving for the past two decades, total emissions will continue to rise without a significant change from business as usual. Our analyses thus indicate that without prompt action, the current rate of GHG emissions from the energy sector would consume the domestic emissions budget well before 2050.

—“Limiting the Magnitude”

The report notes that with the exception of the recent economic downtown, domestic emissions have been rising for most of the past three decades. The US emitted approximately 7 gigatons of CO₂ equivalent in 2008 (the most current year for which such data were available).

A carbon-pricing system is the most cost-effective way to reduce emissions. Either cap-and-trade, a system of taxing emissions, or a combination of the two could provide the needed incentives. While the report does not specifically recommend a cap-and-trade system, it notes that cap-and-trade is generally more compatible with the concept of an emissions budget.

Carbon pricing alone, however, is not enough to sufficiently reduce domestic emissions, the report warns. Strategically chosen, complementary policies are necessary to assure rapid progress in key areas such as: increasing energy efficiency; accelerating the development of renewable energy sources; advancing full-scale development of new-generation nuclear power and carbon capture and storage systems; and retrofitting, retiring, or replacing existing emissions-intensive energy infrastructure.

According to the report, key near-term opportunities for emission reductions include:

• Increase energy efficiency. Enhancing efficiency in the production and use of electricity and fuels offers some of the largest near-term opportunities for GHG reductions. These opportunities can be realized at a relatively low marginal cost, thus leading to an overall lowering of the cost of meeting the 2050 emissions budget.

• Accelerate the use of renewable energy sources. Renewable energy sources offer both near-term opportunities for GHG emission reductions and potential long-term opportunities to meet global energy demand. Some renewable technologies are at and others are approaching economic parity with conventional power sources (even without a carbon-pricing system in place); but continued policy impetus is needed to encourage their development and adoption.

• Address and resolve key barriers to the full-scale testing and commercial-scale demonstration of new-generation nuclear power. Improvements in nuclear technology are commercially available, but power plants using this technology have not yet been built in the United States. The risks of nuclear power such as waste disposal and security/proliferation issues remain as significant concerns and must be successfully resolved.

• Develop and demonstrate power plants equipped with carbon capture and storage technology. Carbon capture and storage needs to be commercially demonstrated in a variety of full-scale power plant applications, to better understand the costs involved and the technological, social, and regulatory barriers that may arise and require resolution.

• Advance low GHG-emitting transportation options. Near-term opportunities exist to reduce GHGs from the transportation sector through increasing vehicle efficiency, supporting shifts to energy efficient modes of passenger and freight transport, and advancing low-GHG fuels (such as cellulosic ethanol).

Research and development of new technologies that could help reduce emissions more cost effectively than current options also should be strongly supported.

Ultimately, however, limiting the magnitude of climate change requires looking beyond these near-term technological opportunities. One reason for having a broader focus is that we know additional technology choices will ultimately be required. As explained earlier, even if the existing “high-impact” technologies were to meet their full technical potential, they themselves are not likely to be adequate to meet the stringent demands of the emissions budgets discussed in Chapter 2. Our current energy system is largely based on R&D that was done two or more decades ago. Basic research could lead to advanced energy efficiency and supply technologies with greatly improved performance, environmental, and economic characteristics.

Another, perhaps more important reason to consider a broader suite of strategies is that many barriers inhibit the deployment of even well-known technologies. For example, the adoption of many energy efficiency technologies and practices requires significant changes in human behavior, lifestyle, and consumer spending practices. New technologies such as CCS are unfamiliar both to the public and to environmental regulators; and if experience is any guide, building the required levels of acceptance for such technologies can be an elusive task. Also inertias in supply chains and interdependent infrastructure systems contribute to slow rates of social and technical change. For these reasons, there is a pressing need for greater understanding of individual and institutional responses to the deployment of new technology.

—“Limiting the Magnitude”

The report recommends seven specific overarching strategies:

1. Adopt an economy-wide carbon pricing system. A system that places a price on greenhouse gas emissions creates incentives for emission reduction efforts and markets for low-emission technologies.

2. Complement the carbon pricing system. Because political realities may inhibit an optimally designed carbon pricing system, and because some emission sources may be relatively insensitive to pricing signals, major emission reductions will also require a portfolio of complementary policies aimed at ensuring rapid progress.

3. Create new technology choices by investing heavily in research and crafting policies to stimulate innovation. US policies to facilitate technological innovation need to be strengthened on a number of fronts. This includes efforts to significantly increase both government and private-sector funding for energy R&D, establish and expand markets for low greenhouse gas technologies and more rapidly bring new technologies to commercial scale, foster workforce development and training, and improve understanding of how social and behavioral dynamics interact with technology.

4. Consider potential equity implications when designing and implementing climate change limiting policies, with special attention to disadvantaged populations. Some low-income/ disadvantaged groups are likely to suffer disproportionately from adverse impacts of climate change, and may also be adversely affected by policies to limit climate change. It will be important to monitor, and to consider options for minimizing, adverse impacts upon these groups. Further, major changes to the energy system will inevitably lead to job gains in some sectors and regions, and losses in others.

5. Establish the United States as a leader to stimulate other countries to adopt greenhouse gas emissions reduction targets.

6. Enable flexibility and experimentation with emission reduction policies at regional, state, and local levels. Considerable state and local-level action to reduce emissions is already underway, and offers a valuable laboratory for policy experimentation and learning. In some instances, it may be appropriate for state/local efforts to be preempted by new federal programs, but this must be balanced against the need to allow for flexibility and innovation.

7. Design policies that balance durability and consistency with flexibility and capacity for modification as we learn from experience. Policies for limiting climate change must remain durable for decades. Durability is enhanced if key constituencies benefit from the policies and therefore have a vested interest in maintaining them. At the same time, policies must be sufficiently flexible to allow for evolution in response to new developments (e.g., in climate change science, in socioeconomic trends, in technological innovation, in our understanding of climate policy impacts). It will be an ongoing challenge to find a balance between these goals of durability and flexibility, the report concludes.

Advancing the Science of Climate Change. The compelling case that climate change is occurring and is caused in large part by human activities is based on a strong, credible body of evidence, says the report Advancing the Science of Climate Change. While noting that there is always more to learn and that the scientific process is never closed, the report emphasizes that multiple lines of evidence support scientific understanding of climate change. The core phenomenon, scientific questions, and hypotheses have been examined thoroughly and have stood firm in the face of serious debate and careful evaluation of alternative explanations.

The report calls for a new era of climate change science where an emphasis is placed on “fundamental, use-inspired” research, which not only improves understanding of the causes and consequences of climate change but also is useful to decision makers at the local, regional, national, and international levels acting to limit and adapt to climate change. Seven cross-cutting research themes are identified to support this more comprehensive and integrative scientific enterprise:

1. Climate Forcings, Responses, Feedbacks and Thresholds in the Earth System
2. Climate-Related Human Behaviors and Institutions
3. Vulnerability and Adaptation Analyses of Coupled Human- Environment Systems
4. Research to Support Strategies for Limiting Climate Change
5. Effective Information and Decision Support Systems Tools and Approaches to Improve Both Understanding and Responses
6. Integrated Climate Observing Systems
7. Improved Projections, Analyses, and Assessments

The report recommends that a single federal entity or program be given the authority and resources to coordinate a national, multidisciplinary research effort aimed at improving both understanding and responses to climate change. The US Global Change Research Program, established in 1990, could fulfill this role, but it would need to form partnerships with action-oriented programs and address weaknesses that in the past have led to research gaps, particularly in the critical area of research that supports decisions about responding to climate change. Leaders of federal climate research should also redouble efforts to deploy a comprehensive climate observing system.

Adapting to the Impacts of Climate Change. Reducing vulnerabilities to impacts of climate change that the nation cannot, or does not, avoid is a highly desirable strategy to manage and minimize the risks, says the third report, Adapting to the Impacts of Climate Change. Some impacts—such as rising sea levels, disappearing sea ice, and the frequency and intensity of some extreme weather events like heavy precipitation and heat waves—are already being observed across the country.

The report notes that policymakers need to anticipate a range of possible climate conditions and that uncertainty about the exact timing and magnitude of impacts is not a reason to wait to act. In fact, it says, boosting US adaptive capacity now can be viewed as “an insurance policy against an uncertain future,” while inaction could increase risks, especially if the rate of climate change is particularly large.

Although much of the response to climate change will occur at local and regional levels, a national adaptation strategy is needed to facilitate cooperation and collaboration across all lines of government and between government and other key parties, including the private sector, community organizations, and nongovernmental organizations. As part of this strategy, the federal government should provide technical and scientific resources that are lacking at the local or regional scale, incentives for local and state authorities to begin adaptation planning, guidance across jurisdictions, and support of scientific research to expand knowledge of impacts and adaptation.

Adapting to climate change will be an ongoing, iterative process, the report says, and will involve decision makers at every scale of government and all parts of society. A first step is to identify vulnerabilities to climate change impacts and begin to examine adaptation options that will improve resilience. To build the scientific knowledge base and provide a basis for increasingly effective action in the future, adaptation efforts should be monitored and analyzed to judge successes, problems, and unintended consequences. The report also calls for research to develop new adaptation options and a better understanding of vulnerabilities and impacts on smaller spatial scales.

Adaptation to climate change should not be seen as an alternative to attempts to limit it, the report emphasizes. Rather, the two approaches should be seen as partners, given that society’s ability to cope with the impacts of climate change decreases as the severity of climate change increases. At moderate rates and levels of climate change, adaptation can be effective, but at severe rates, adapting to disturbances caused by climate change may not be possible, the report says.

Two additional reports. America's Climate Choices also includes two additional reports that will be released later this year: Informing an Effective Response to Climate Change will examine how to best provide decision makers information on climate change, and an overarching report will build on each of the previous reports and other work to offer a scientific framework for shaping the policy choices underlying the nation’s efforts to confront climate change.

The project was requested by Congress and is funded by the National Oceanic and Atmospheric Administration.

Resources

• Panel roster for Advancing the Science of Climate Change

• Panel roster for Limiting the Magnitude of Future Climate Change

• Panel roster for Adapting to the Impacts of Climate Change

• America’s Climate Choices

• Advancing the Science of Climate Change

• Limiting the Magnitude of Climate Change

• Adapting to the Impacts of Climate Change