The urgency of the rate and magnitude of climate change and the complexity of interactions across risks and responses mean that the next decade will require immediate investments in coordinated research to protect human systems and ecosystems from the risks described in Chapter 2. Research is required to support decision making that integrates climate risk-management strategies and policies. The primary strategies are (1) mitigation, reducing global emissions and removing CO2 from the atmosphere; and (2) adaptation, preparing for and managing the harmful effects of global change. These strategies can be reinforcing or have unintended, and potentially negative, consequences. Solar geoengineering—the deliberate large-scale manipulation of an environmental process that modifies the amount of solar heating of the Earth—is another strategy that requires further research to better understand its technical and social feasibility, as well as how such measures could interact with mitigation and adaptation in ways that may introduce additional risk.
Because adaptation was extensively covered in Chapter 2, the primary focus of this chapter is on mitigation and solar geoengineering. In addition, Chapter 3 introduced important social science needs required to understand how to achieve emissions reductions for policy design and through behavior change that include considerations of ethics, equity, technical potential, adoption, and path dependencies.
Many strategies for reducing emissions or removing carbon from the atmosphere have implications for the kinds of risks noted in Chapter 2, underscoring the need for an integrated research approach. In some cases, a technological solution may affect natural systems, such as the potential for solar geoengineering to change the levels of
ultraviolet light received by plants, with potential implications for agricultural productivity and ecosystem health (NRC, 2015). In other cases, there may be opportunities to make natural systems more resilient while also limiting the overall impact of climate change, for example strategies to enhance storage of carbon in natural systems are often similar or identical to strategies that improve soil health and water retention in the landscape (NASEM, 2019a).
Although one objective of the 2012 Strategic Plan recognized the need to “enhance the usability of scientific knowledge in supporting responses to global change” (USGCRP, 2012, Objective 1.2: Science for Adaptation and Mitigation), to date the program has not included a major emphasis on understanding the effectiveness of these risk-management strategies or associated benefits, costs, and equity impacts. Yet, such an understanding is an essential input into decision making at multiple levels.
The ultimate requirement to avoid additional climate change risk involves reducing net anthropogenic emissions of the forcing gases to zero. In 2030, the United States is projected to emit only 11 percent to 12 percent of global emissions of fossil and industrial CO2, the dominant greenhouse gas (GHG), with this share projected to decrease over time (IEA, 2020). Thus, in addition to understanding the effectiveness of emissions reduction strategies within the United States, it is critical for the U.S. Global Change Research Program’s (USGCRP’s or “Program’s”) research efforts to consider how U.S. actions and decisions can most beneficially affect those of other countries. This influence comes from active U.S. participation in the cooperative programs referenced in Chapter 1, which is usefully supplemented by additional effort to develop techniques to measure GHGs on national and smaller scales to build confidence in national emissions pledges. Difficult-to-measure emissions from soils deserve special attention. Other crucial channels of influence include leadership in the global institutions that coordinate discussions on the control of GHG emissions, formulate international climate developments, and marshal financial and technical aid for developing regions. Climate action within the private sector is a vital part of this engagement, because supply chains span the globe, and standards and practices adopted by firms in one nation often influence those employed elsewhere.
Here, the committee focuses on USGCRP’s mitigation research in three areas: setting science-based mitigation goals, improving emissions measurement and monitoring, and exploring a range of CO2 removal and sequestration techniques. Many mitigation
measures provide a joint benefit in increasing the security of particular U.S. sectors through a simultaneous contribution to efforts to adapt to a changing climate. However, also important to consider is the range of risks associated with different mitigation approaches. For example, CO2 removal and sequestration technologies themselves pose various and substantial risks and uncertainties, with respect to water, energy demand, land-use and costs that require research to better understand their efficacy and potential to reduce net emissions in a changing climate (NASEM, 2019a).
Enhance the Scientific Basis for Mitigation Goals
The choice among widely discussed global climate mitigation goals (e.g., limiting global warming to 1.5 or 2°C) needs to be strongly informed by science (IPCC, 2018). For example, recent emphasis on limiting global warming to 1.5 rather than 2°C arose in part from improved understanding of how much sea level is likely to rise at 2°C of warming over what timescales, particularly from the contributions of large land ice sheets in Greenland and the Antarctic. That understanding, however, is far from complete, and as it is refined, policy goals may be altered.
Informing top-line mitigation goals (e.g., limiting warming to 1.5 or 2°C) requires understanding the sensitivity of climate to human forcing and the physical manifestations of different levels of emissions; the environmental and socioeconomic consequences of climate change under different levels of mitigation; and the socioeconomic consequences of the mitigation (and adaptation) strategies for different populations and regions, including implications for equity. In turn, the effects of social change on GHG emission and land use, including the effectiveness of programs and policies intended to reduce emission, need to be considered in scenarios used for modeling. Acknowledging there is sufficient information to take urgent action now (Gilbert and Sovacool, 2016; Wara, 2015; Wara et al., 2015), this fuller understanding of the global societal consequences of different levels of warming could inform additional actions to refine and meet mitigation targets. Achieving fuller understanding of the socioeconomic consequences of climate change is a major motivation for greater integration of multidisciplinary research, particularly natural and social sciences. Some consequences are amenable to sector-by sector treatment, whereas others, such as migration pressure and possible political instability, are more crosscutting.
Understanding the physical and socioeconomic implications of different levels of global warming is also foundational to adaptation planning. For that purpose, this information needs to be produced at the local spatial scale.
Improve Emissions Measurement and Monitoring
Accurate measurement and reporting of anthropogenic emissions of GHGs at the national scale is foundational to controlling global GHG emissions. This means measuring emissions from fossil fuel burning and from direct human intervention in the land sector (land use and land-use changes), such as deforestation.
In the context of the United Nations Framework Convention on Climate Change (UNFCCC) reporting, nations are encouraged to use GHG emissions-measurement methods issued by the IPCC (2006, 2019c). For many sectors, a hierarchy of methods (of increasing complexity and accuracy) is presented. These methods emphasize “bottom-up” approaches based on knowledge of human activities. For example, fossil fuel emissions are estimated based on reported fuel usage together with information about the carbon content of the fuel. These are distinct from “top-down” approaches that are based on measured changes in concentrations of CO2 in the atmosphere. Both approaches are needed.
Emissions are estimated by the emitting nations themselves and reported to the UNFCCC. The current international agreement provides for independent review by technical experts of self-reported emissions. Even so, confidence in self-reported emissions is limited by a general lack of methods and data to independently verify them. The accuracy of reported emissions is limited by factors including lack of capacity for making estimates (particularly in the developing world) and data gaps, and by incentives to report inaccurate emissions for political, financial, or economic purposes.
Research on scientific measurement of GHG emissions should identify methods that will be effective in the context of likely policy approaches to emissions verification. Many of the recommendations in previous National Academies reports (NASEM, 2018; NRC, 2010c) on characterizing and verifying emissions are still relevant today, including: maintaining essential surface and satellite observations networks, supporting data assimilation systems, expanding gridded inventories, and coupling top-down and bottom-up approaches.
Explore CO2 Removal, Reliable Sequestration, and Utilization
Mitigating GHG concentrations necessarily involves cutting global GHG emissions. This response may be supplemented, however, by activities that remove CO2 from the atmosphere and either store it or convert it to some other form (NASEM, 2019a). Research on the mitigation of domestic U.S. emissions—including the development of technologies to aid replacement of fossil fuels, and federal, state, local, and tribal
control measures—is ongoing in agencies outside the normal scope of USGCRP activities. CO2 removal, on the other hand, falls outside purely domestic efforts, and merits treatment within a wider USGCRP concern with issues of global scope. Applications of direct removal technology may involve similar multination efforts. As mentioned above, different carbon removal and storage approaches come with different associated risks to the systems identified in Chapter 2 (e.g., food, water, and energy), which also require attention and research in the context of other approaches.
Additionally, only a small fraction of the CO2 and methane emitted each year is currently being captured and used, and most technologies to utilize captured carbon are in their infancy. However, these technologies have a role to play in future carbon management and the overall portfolio of mitigation strategies. A recent National Academies report (NASEM, 2019b) found that carbon utilization needs to be done at scale, which will depend on the pace of technology development and future energy, market, and regulatory landscapes. The report also found that, like all technologies, “a comprehensive evaluation of carbon utilization technologies would include evaluation at various maturity levels based on economic, market, regulatory, and environmental factors” (NASEM, 2019b, p. 4). There are other integrating factors across human and natural systems of global change to be considered in further technology development that may involve social or regulatory barriers and incentives as well as disruptive change to energy and material manufacturers. Better integration of current research efforts is needed to advance progress in this space (NASEM, 2019b).
Climate change currently affects the security of the American people and the nation across many systems including human health, food, water and energy, with projections concluding that, without considering adaptation, each additional unit of warming would further increase nearly all risks with the risks differentially affecting different ecosystems, regions, and human populations. Adapting to these risks has been on USGCRP’s research agenda for the past two decades. However, new research, enhanced coordination, and expanded communication efforts are needed to advance society’s ability to adapt to risks arising sooner and more intensely than projected, within the context of increasingly complex interactions among these security risks (Janetos, 2020). Further, longer-term evaluation is needed to monitor the effectiveness of adaptation options over time to identify adjustments needed to enhance resilience.
Advancing an integrated understanding of security risks was the focus of Chapter 2. This integrated understanding is an important component of research needed to
inform efforts to adapt to climate change. In addition, the research of USGCRP and participating agencies will increasingly require engaging in ongoing discussions with decision makers to support specific adaptation decision needs. Examples of these sorts of research questions are provided in Box 4.1 for coastal communities.
“Solar Geoengineering” approaches aim to limit climate change through a variety of climate interventions that modify the amount of solar heating of the Earth. Not enough is known about these approaches and their potential impacts to consider deploying them today, but concerns that mitigation and adaptation efforts will be insufficient to avoid the worst consequences of climate change have motivated a call for increased research on solar geoengineering in case it is needed in the future (NRC, 2015).
Possible solar geoengineering approaches include widespread distribution of small reflective particles in the stratosphere, augmentation of reflective cloud cover in the lower atmosphere, or reduction of cirrus clouds in the upper troposphere that trap outgoing radiation. While these approaches could potentially reduce global atmospheric temperature and reduce some near-term risks of climate change, they could also introduce new risks—such as reduction in stratospheric ozone, shifts in precipitation patterns, or impacts on ecosystems—with potential implications for geopolitical instability (NASEM, 2021b). Indeed, even research on the feasibility of solar geoengineering has raised concerns about the “moral hazard” involved—specifically the notion that holding out the promise of these options in the future might forestall efforts to mitigate and adapt to climate change now (NASEM, 2021b).
A 2015 National Academies report anticipated several scenarios in which it would be beneficial to understand the risks and opportunities involved with sunlight reflection strategies. That report recommended that research on these strategies be expanded and that a serious deliberative process be undertaken to examine what sort of research governance is needed—emphasizing that open conversations, with civil society engagement, should be part of the process of oversight for any research efforts undertaken. However, investments in this research are still very modest.1
The National Academies launched a consensus study in 20192 to develop a detailed transdisciplinary research agenda and recommend research governance approaches for solar geoengineering. The study committee was tasked to identify a wide range of research needs spanning feasibility, efficacy, and risks; to provide detailed guidance on research design and research governance; and to discuss mechanisms to ensure
transparency, accountability, and legitimacy of the research outcomes. The recommendations from the National Academies consensus report on this topic (NASEM, 2021b) are relevant to USGCRP’s mission and mandate and should be carefully considered by the Program.
Research on solar geoengineering spans the range of physical, ecological, and social sciences that contribute to global change research. To be successful, such research will also need to coordinate a number of stakeholders in the U.S. scientific community, including USGCRP participating agencies, as well as to foster collaboration and consideration of relevant international programs and activities. As such, the committee sees the potential for USGCRP to play a pivotal role in advancing this research, particularly if the Program takes steps to improve both its disciplinary representation and its efforts to engage stakeholders in defining research priorities.
Integrated systems-based research is urgently needed to describe and quantify the complexities of interactions across sectors, regions, and decision-making entities, considering the interdependence, synergies, and trade-offs among mitigation, adaptation, solar geoengineering, and strategies to address other societal priorities. For example, many risk-reducing actions decrease both the human activities driving change and the damage from climate change that cannot be stopped.