Decisions about how to limit the magnitude of climate change, by how much, and by when demand input from research activities that span the physical, biological, and social science disciplines as well as engineering and public health. In addition to assessing the feasibility, costs, and potential consequences of different options and objectives, research is critical for developing new and improving existing technologies, policies, goals, and strategies for reducing GHG emissions. Scientific research, monitoring, and assessment activities can also assist in the ongoing evaluation of the effectiveness and unintended consequences of different actions or set of actions as they are taken—which is critical for supporting adaptive risk management and iterative decision making (see Box 3.1). This section highlights some pressing research needs related to efforts to limit the magnitude of future climate change.
Commonly discussed strategies for limiting climate change (see Figure 4.2) include reducing energy consumption, for instance by improving energy efficiency or by reducing demand for energy-intensive goods and services; reducing emissions of GHGs from energy production and use, industrial processes, agriculture, or other human activities; capturing CO2 from power plants and industrial processes, or directly from the atmosphere, and sequestering it in geological formations; and increasing CO2
uptake by the oceans and land surface. There is also increasing interest in solar radiation management and other geoengineering approaches (see Chapters 9, 14, and 15). While much is known about some of these strategies, others are not well understood, and there are many scientific research needs related to the development, improvement, implementation, and evaluation of virtually all technologies, policies, and other approaches for limiting climate change.
Setting goals for limiting the magnitude of climate change involves ethical and value questions that cannot be answered by scientific analysis. However, scientific research can help inform such efforts by providing information about the feasibility and potential implications of specific goals. The companion report Limiting the Magnitude of Future Climate Change (NRC, 2010c) suggests that the U.S. goal be framed in terms of a cumulative budget for GHG emissions over a set time period. The report does not recommend a specific budget goal, but it examines a "representative" budget in the range of 170 to 200 Gt CO2-eq2 for the period 2012 to 2050.3 As the Limiting report notes, reaching a goal in this range will be easier and less costly overall if actions to limit GHG emissions are undertaken sooner rather than later. It will also require pursuing multiple emissions-reduction strategies across a range of sectors, as well as continued research and development aimed at creating new emissions-reduction opportunities. Finally, to support adaptive risk management and iterative decision making with re
2 Gt CO2-eq indicates gigatons (or billion tons) of CO2 equivalent emissions; this metric converts emissions of other GHGs to an equivalent concentration of CO2.
3 This range was derived from recent integrated assessment modeling exercises carried out by the Energy Modeling Forum (http://emf.stanford.edu).
spect to emissions reductions or other climate goals, scientific research will be needed to monitor and improve implementation approaches and to evaluate the potential trade-offs, co-benefits, and unintended consequences of different strategies, as well as the interaction of multiple approaches working in concert. These and other examples of research needs for supporting actions to limit climate change are listed in Table 4.4.
The challenge of limiting climate change also engages many of the other research themes identified in this chapter. For example, understanding and comparing the full effects of various energy technologies or climate policies (including their comparative benefits, costs, risks, and distributional effects) typically requires an integration of climate models with energy and economic models (Theme 7), which in turn are based on fundamental understanding of the climate system (Theme 1) and human systems
TABLE 4.4 Examples of Research Needs Related to Limiting the Magnitude of Climate Change (from Part II)
• Advance the development, deployment, and adoption of energy and transportation technologies that reduce GHG emissions.
• Develop and evaluate strategies for promoting the use of less-emission-intensive modes of transportation.
• Characterize and quantify the contributions of urban areas to both local and global changes in climate, and develop and test approaches for limiting these contributions.
• Continue to support efforts to improve energy efficiency in all sectors and develop a better understanding of the obstacles to improved efficiency.
• Improve understanding of behavioral and sociological factors related to the adoption of new technologies, policies, and practices.
• Develop and improve integrated approaches for evaluating energy services in a systems context that accounts for a broad range of societal and environmental concerns, including climate change.
• Develop and improve technologies, management strategies, and institutions to reduce net GHG emissions from agriculture, while maintaining or enhancing food production potential.
• Assess the potential of land, freshwater, and ocean ecosystems to increase net uptake of CO2 (and other GHGs) and develop approaches that could take advantage of this potential without major adverse consequences.
• Improve understanding of links between air quality and climate change and develop strategies that can limit the magnitude of climate change while improving air quality.
• Improve understanding of the potential efficacy and unintended consequences of solar radiation management approaches and direct air capture of CO2, provided that this research does not detract from other important research areas.
• Establish and maintain monitoring systems capable of supporting evaluations of actions and strategies taken to limit the magnitude of future climate change, including systems that can verify compliance with international GHG emissions-reduction agreements.
(Theme 2), as well as the observations (Theme 6) that underpin such understanding. Similarly, setting and evaluating goals and policies for limiting the magnitude of future climate change involves decision-making processes at a variety of scales that would benefit from decision-support tools that aid in handling uncertainty and understanding complex value trade-offs (Theme 5). These decisions would similarly benefit from integrated analyses or linked "end-to-end" models (Theme 7) of how policies and other actions influence emissions, how the climate system and related environmental systems will respond to these changes in emissions, and how human and natural systems will be affected by all of these changes—all of which again depend critically on observations (Theme 6). Thus, while the following subsections describe a number of key research needs related to limiting the magnitude of future climate change, progress in many other research areas will also be needed.
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