The climate system is highly complex as are the human institutions that are affected by and that must respond to climate change

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The difficulty of developing sound strategies for responding to climate change, and of building public support for such strategies, stems in part from the inherent complexity of the issue. Some of this complexity relates to the physical science of climate change; but understanding and responding to climate change also raises many social, economic, ethical, and political challenges. The chapter highlights some of the unique challenges posed by climate change that must be considered in designing the nation's response strategies.

There are complex linkages among emissions, concentrations, climate changes, and impacts. Projecting future climate change requires understanding numerous linkages among human activities, greenhouse gas (GHG) emissions, changes in atmospheric composition, the response of the climate system, and impacts on human and natural systems. The basic links in this chain are well understood, but some elements (in particular, projecting specific impacts at specific times and places) are much less so. As a result, the outcomes of actions to reduce emissions or to reduce the vulnerabilities of human and natural systems must often be presented in probabilistic or qualitative terms, rather than as certain predictions.

Lack of certainty about the details of future climate change is not, however, a justification for inaction. People routinely take actions despite imperfect or incomplete knowledge about the future in situations such as buying home insurance, saving for retirement, or planning business strategies. Likewise, people use probability data from weather forecasts to decide if they should take an umbrella to work, move a scheduled outdoor event indoors, or cancel a ball game. Indeed, it could be argued that uncertainty about future climate risks is a compelling reason for taking proactive steps to reduce the likelihood of adverse consequences.

There are significant time lags in the climate system. It takes very long time periods (decades to millennia) for some aspects of the climate system to respond fully to



changes in atmospheric GHG concentrations.1 This is because the world's oceans can store a large amount of heat—so it takes a long time for the climate system to warm up in response to changes in GHG concentrations2—and because impacts such as sea level rise and the melting of ice sheets can take several centuries or even millennia to be fully expressed. Some GHGs (such as methane) are removed from the atmosphere within about a decade, but CO2 persists much longer—approximately 20 percent of the CO2 emitted today will remain in the atmosphere more than a millennium from now.3 Thus, a failure to reduce GHG emissions in the near-term will "lock in" a certain amount of future climate change for decades, if not centuries, to come.

There are also significant time lags in human response systems. GHG emissions are to a large extent built into societal infrastructure (e.g., buildings, power plants, settlement and transportation patterns) and into human habits and organizational routines, few of which change quickly. Market incentives affecting capital investments leave little room for considering consequences on century or longer time scale. Nevertheless, making major reductions in GHG emissions and preparing to adapt to the effects of climate change will require transformative changes, for instance, in how the country produces and uses energy (see Box 3.1), builds buildings and transportation infrastructure, and manages water and other natural resources. It will likewise require significant changes in consumer choices, travel behavior, and other individual and household-level decisions. Overcoming the inertia of the status quo in advancing these sorts of transformations will pose challenges for government, industry, agriculture, and individual citizens alike.

An issue of particular concern is that much of the equipment and infrastructure that leads to GHG emissions (e.g., roads, vehicles, buildings, power plants) have lifetimes of decades. There are often strong economic pressures to continue use of such equipment and infrastructure, rather than retrofitting or replacing with a lower-emitting option. Making substantial emission reductions within the next few decades will require accelerating this turnover faster than projected business-as-usual rates.4

Risks, judgments about risk, and adaptation needs are highly variable across different contexts. Different regions, economic and resource sectors, and populations will experience different impacts from climate change, will vary in their ability to tolerate and adapt to such impacts, and will hence differ in their judgments about the potential risks posed by climate change. For instance, coastal communities that are vulnerable to serious disruptions could be expected to view the risks of climate change as quite serious. Actions that are taken in response to climate change will also pose differing types of risks to different regions, sectors, and populations. For instance, f N

BOX 3.1 The U.S. Energy System

The U.S. energy system includes a vast and complex set of interlocking technologies for the production, distribution, and use of fuels and electricity.0 This includes technologies that convert primary energy resources (e.g., nuclear energy, renewable sources such as solar and wind, and the fossil fuels coal, oil, and natural gas) into useful forms such as gasoline and electricity; technologies that transmit this energy to consumers (e.g., electrical transmission and distribution systems, gas pipelines); technologies that store or utilize this energy (e.g., batteries, motors, lights, home appliances); and associated demand-side technologies that control energy use (e.g., advanced electricity metering systems). Another key component of this system is the people that use the energy—their behaviors and preferences play a major role in shaping energy technologies.

Currently, the United States relies on carbon-based fossil fuels for more than 85 percent of its energy needs. This dependence evolved not only because fossil fuels were available at low market costs but also because their physical and chemical properties are well suited to particular uses: petroleum for transportation; natural gas as an industrial feedstock, for residential and commercial space heating, and more recently as a fuel for electric power generation; and coal for the generation of electricity and as a feedstock for some industrial processes. Indeed, almost all consumer-based, industrial, and governmental activities require the consumption of fossil fuels, either directly or indirectly.

Absent strong and sustained policy intervention, fossil fuels are projected to remain the nation's primary source of energy for the foreseeable future. Compared with alternative sources of energy, fossil fuels would likely remain relatively inexpensive to produce, and they would continue to benefit from past investments in vast existing infrastructure—investments that would need to be duplicated (in whole or in part) to enable wide-scale displacement by alternative energy sources. The nation's reliance on carbon-based fossil fuels would only be significantly reduced in the near-term if the prices of those fuels were increased to reflect the full social costs of their extraction, transformation, distribution, and use; and only if there are incentives to encourage research and development aimed at reducing the cost and promoting the commercialization of alternative energy sources.

a The material in this box was adapted from NRC, America's Energy Future: Technology and Transformation: Summary Edition (Washington, D.C.: National Academies Press, 2009).

individuals and organizations that are heavily invested in carbon-intensive industries may prefer to face the risks of climate change impacts rather than face the potential costs of policies to limit GHG emissions. Decision makers will thus inevitably face some difficult choices and trade-offs in seeking to protect the interests of different constituencies.


Decisions affecting climate change are made at all levels of society. The federal government can play a critical leadership role in setting policies that affect the actions of all parts of society. But much of the responsibility and opportunity for responding to climate change rests with state and local governments and with the private sector (which accounts for most of the nation's capital investments, industrial production, and employment). Decisions made at the individual and household level also play a major role in driving GHG emissions, and of course, public support is critical for motivating political leaders to take actions in response to climate change. A U.S. strategy for responding to climate change must therefore include careful consideration of which information, incentives, and regulations (provided by which level of government) will most effectively engage and facilitate wise decision making by these multiple actors. In some cases, the appropriate federal role may be limited to decision support, while in other contexts, more active policy guidance and coordination power are needed.

Limiting climate change requires global-scale efforts. A molecule of CO2 emitted in India or China has the same effect on the climate system as a molecule emitted in the United States. There is wide agreement that limiting the magnitude of climate change will require substantial action on the part of all major GHG-emitting nations, including both the industrialized nations and the rapidly developing countries whose relative share of global emissions is rapidly increasing (see Figure 3.1). Yet there are many different perspectives on how to define each country's responsibilities for contributing to the global effort.5 Some argue that U.S. action must be conditioned on actions by other nations, given the economic disadvantages that the country might face if it committed to significant emission reductions without similar commitments from other nations. Others argue that the United States, as the country with largest historical share of GHG emissions and with one of the highest per capita GHG emission rates, has an ethical obligation to substantially reduce domestic emissions, even in the absence of commitments from other nations. Still others suggest that there will be substantial economic advantages in leading the development of new technologies to deal with climate change. There is no simple way to reconcile these different views, but it is clear that strong, credible U.S. policies for reducing domestic emissions will help advance international-level efforts to do the same.

Climate change is one of multiple, interconnected challenges. Climate change is just one of many interacting factors affecting humans and their environment. Coastal environments, for example, are being affected not only by GHG-driven changes such as sea level rise, ocean acidification, changes in air and water temperature, and precipitation and storm patterns, but also by pollution runoff, invasive species, coastal development,

2007 2015 2020 2025 2030 2035

FIGURE 3.1 World energy-related CO2 emission projections (in billion metric tons CO2), by OECD (Organization for Economic Cooperation and Development) and non-OECD countries over the period 2007-2035. Non-OECD countries include developing, newly industrialized, and Eastern European and former Soviet countries. For a list of OECD and non-OECD countries, see: SOURCE: Energy Information Administration / International Energy Outlook. 2010.

2007 2015 2020 2025 2030 2035

FIGURE 3.1 World energy-related CO2 emission projections (in billion metric tons CO2), by OECD (Organization for Economic Cooperation and Development) and non-OECD countries over the period 2007-2035. Non-OECD countries include developing, newly industrialized, and Eastern European and former Soviet countries. For a list of OECD and non-OECD countries, see: SOURCE: Energy Information Administration / International Energy Outlook. 2010.

and overfishing. These different issues are often studied and managed as isolated matters, without recognizing and accounting for interconnected causes and interactive effects. Likewise on a broader global scale, many different issues affect and are affected by climate change—such as food production, water supplies, human health, energy production and use, economic development, security concerns—but these are seldom addressed in an integrated manner.

These sorts of inter-linkages not only pose difficult challenges, but also offer important opportunities for alleviating multiple problems simultaneously. For instance, integrated management plans for protection of coastal zones can help alleviate many of the climate-related and non-climate-related concerns listed above. Actions taken to reduce fossil fuel use can offer substantial benefits for human health (by reducing emissions of conventional air pollutants) and for national security (by reducing dependence on imported energy sources).6

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