West, T. O., N. P. Gurwick, M. E. Brown, R. Duren, S. Mooney, K. Paustian, E. McGlynn, E. L. Malone, A. Rosenblatt, N. Hultman, and I. B. Ocko, 2018: Chapter 18: Carbon cycle science in support of decision making. In Second State of the Carbon Cycle Report (SOCCR2): A Sustained Assessment Report [Cavallaro, N., G. Shrestha, R. Birdsey, M. A. Mayes, R. G. Najjar, S. C. Reed, P. Romero-Lankao, and Z. Zhu (eds.)]. U.S. Global Change Research Program, Washington, DC, USA, pp. 728-759, https://doi.org/10.7930/SOCCR2.2018.Ch18.
Carbon Cycle Science in Support of Decision Making
Carbon cycle science supports decisions in a number of national and international contexts. For example, decisions about managing ecosystems such as national or state forests require integrating stakeholder perspectives with scientific input on the consequences or alternative policy approaches for ecosystems, emissions, and climate (BLM 2016). At the international level, as countries establish goals to stabilize carbon and GHG concentrations in the atmosphere, the scientific community should play an important role in assessing carbon budgets and developing the technologies, methods, and practices for reducing net GHG emissions and managing carbon stocks. Global efforts to slow deforestation, improve human health, and decrease global GHG emissions will be aided by substantial input from the international scientific community and respective national agencies. In all of these examples, and many others, improvements in the quality and process of scientific input can help inform sound decision making. Recent research on CH4 emissions provides a notable example of fundamental carbon cycle science used in decision making. Reducing anthropogenic CH4 emissions has become a high priority for policymakers, given the potential for near-term climate benefits and the relative tractability1 of monitoring and mitigating emissions from many sectors. Concerted effort to develop relationships among scientists and decision makers has enabled progress in identifying information needs, developing technology to provide needed information, and establishing science questions that evaluate existing knowledge. With respect to policy drivers, new laws and rules have been enacted to mitigate and measure CH4 emissions in California and other key regions and sectors in the United States (Federal Register 2016a, 2016b). Atmospheric or “top-down” scientific methods for detecting, quantifying, and attributing CH4 fluxes have dramatically improved. For example, satellite observations have enabled scientists to identify concentrated regions of CH4 emissions, information relevant to policy and management that previously had not been well known or understood (Kort et al., 2014). Recent field studies have revealed evidence of a long-tail statistical distribution of emissions sources in the U.S. natural gas supply chain, where a relatively small number of superemitters dominate key regions and sectors (Brandt et al., 2014; Zavala-Araiza et al., 2015; Zimmerle et al., 2015). Some stakeholders (e.g., California Air Resources Board) already have applied the atmospheric and field research findings to make corrections to CH4 inventory estimates. Additionally, recent advances in remote sensing of CH4 point sources (Frankenberg et al., 2016; Thompson et al., 2016) demonstrate the potential to efficiently detect leaks from point sources.
Because the demand for tailored knowledge is often urgent, specific, and only weakly aligned with incentives that drive fundamental research, consulting firms and non-governmental organizations (NGOs) have often met this demand. These institutions have generated a great deal of user-driven science over the decades. For example, the World Wildlife Fund (WWF) and the Carbon Disclosure Project (CDP) partnered with multiple, large, U.S.-based corporations to produce The 3% Solution, an analysis of the business case for businesses to achieve net savings of up to $190 billion by 2020 through measures to reduce carbon emissions (WWF and CDP 2013). Woods Hole Research Center, in collaboration with the U.S. Agency for International Development (USAID), produced a map of aboveground carbon stocks in Mexico. The map built on information already assembled by Mexico’s government for its National Forest Inventory and met a clear need to advance the estimates of Mexico’s forest carbon stocks at both national and municipal levels (Cartus et al., 2014; WHRC 2014). As these examples illustrate, contract-driven science is sometimes made publicly available, such as when governmental agencies provide funding to support projects in the public interest or when private-sector entities and NGOs partner to develop analyses of common interest. However, the private contract model has limitations. Many products of contract research remain outside the public domain, and users without the resources to purchase these goods cannot easily access tailored information for their decision-making needs. User institutions that lack these resources are typically smaller and also have less influence than their larger counterparts in a variety of forums. This imbalance in access to information has profound implications because, as many chapters in this report demonstrate, carbon management has consequences for all of society, not only the entity making a particular decision. Because user-driven science that does not enter the public domain is difficult to access, further characterization of its contributions or extent are not included in this chapter. In spite of this, significant effort should be placed on accessing relevant science that is outside the public domain in order to determine whether this science has sufficient value to impact the decision-making process.
18.3.1. Use of Carbon Cycle Science for Land Management
The carbon research community performed a great deal of work in the past decade with the aim of improving decision making in agriculture, energy production and consumption, building infrastructure design and maintenance, transportation, and many other sectors that consume fossil fuels or generate land-based emissions. This research filled knowledge gaps that helped decision makers understand multiple impacts of land-management decisions. Research foci included, for example, ecosystem disturbance (e.g., fire and pest outbreaks), human health and risk, indirect land-use change, efficient production throughout commodity supply chains, full life cycle energy and emissions impacts of ecosystems and production systems, and how these analyses change under alternative land-management scenarios. Federal guidance to U.S. agencies documents how full GHG accounting has been incorporated into environmental impact analyses under current and alternative scenarios (Federal Register 2016b). Briefly illustrated here is the potential impact of scientific input on land management through examples of land-use policy and of terrestrial management on the carbon cycle.
The use of carbon cycle science for decisions on carbon emissions reductions in agriculture is relevant for a wide suite of societal and policy questions relating to the direct impacts of land-use decisions on energy, emissions, health, and ecosystems (see Ch. 5: Agriculture). For example, carbon cycle science from multiple disciplines informs dialogue and decisions about the role biofuels can play in the energy economy. Biofuels can include dedicated energy crops, agricultural wastes and residues, and CH4 from agricultural wastes. The use of biofuels can decrease GHG emissions, depending on net changes in biomass growth stocks across the landscape (e.g., harvest rates, deforestation, and indirect land-use change) and on the net efficiency of converting biomass to energy (see Ch. 3: Energy Systems). Biofuel policy options have complex and highly variable implications for carbon emissions that are a function of energy expended in production, processing, and use of biofuels; indirect land-use change; and ecological and economic costs and benefits of biofuels (Paustian et al., 2001). In seeking solutions to energy, environmental, and food challenges, biofuels can either contribute positively or negatively to existing societal issues (Tilman et al., 2009). Full carbon cycle analysis and modeling are key to ensuring that policies and resulting actions actually lower carbon emissions instead of raising them. Such analyses continue to be used to ascertain the benefit of biomass to reduce net emissions, including biomass burning (Cherubini et al., 2011; Johnson 2009; Khanna and Crago 2012; Miner et al., 2014; Mitchell et al., 2012; Tian et al., 2018) and forest thinning to reduce wildfire risks (Campbell et al., 2012; Mitchell et al., 2009). Analyses at different spatial scales (e.g., plot, national, and global) and temporal scales (e.g., years, decades, and centuries) can yield different conclusions for land-related carbon issues, indicating the need to synthesize or integrate approaches used across scales (i.e., plant growth models, land-use change models, integrated assessment models (IAMs), and natural resource supply models).
18.3.2 Carbon Management Strategies
While some carbon management strategies are still being debated within the science community, a number of strategies have been well documented and quantified. Some of them are summarized from results in preceding chapters of this report (see Table 18.1). Many land-based strategies are associated with changes in management. Humans have a long history of altering the landscape and associated carbon stocks around the world since initial settlement and population expansion (Sanderman et al., 2017; Köhl et al., 2015). People have changed forests to agricultural areas and vice versa; changed management of soils, forests, grasslands, and other ecosystems; and developed urban and suburban areas. There is a robust literature of observations and carbon stock comparisons under different land uses and management regimes that provides guidance for managing natural resources, fossil resources, and renewables with regard to carbon. Potential sequestration rates have been estimated by aggregating data from hundreds of paired plots, and the data have been used for national scale estimates (U.S. EPA 2016) and global default values for numerous management practices across land, energy, and transportation sectors (IPCC 2006). Research has moved beyond estimating the influence of management changes within a sector, to evaluating how change in one land or energy sector causes changes in other land or energy sectors.
Table 18.1. Summary of Options, Capacity, and Co-Effects for Reducing Greenhouse Gases (GHGs) in North Americaa Activity Impact on GHGs Potential Reductionb Co-Effects
|Activity||Impact on GHGs||Potential Reductionb||Co-Effects|
|Afforestation and improved forest management (Ch. 9, 12)c||Increase in net removals from the atmosphere.|
Reduction in emissions by avoiding the conversion of forests and grasslands to other cover types.
Increase in carbon removals from the atmosphere by promoting the conversion of other land covers to forests or grasslands.
|30 to 330 teragrams of carbon (Tg C) per year (U.S. only)||Potential impacts on food production, biodiversity, net forest resources, and counter harvesting elsewhere (i.e., leakage), resulting from increased forestland area.|
|Managing grasslands (Ch. 10)c||Increase in net removals from the atmosphere and in biomass and soil carbon storage by improving grazing practices and grasslands management.||Tens of Tg C per year (U.S. only)||Shifts in species composition.|
|Reducing methane (CH4) emissions from livestock (Ch. 5)c||Reduction in net agriculture emissions by controlling livestock CH4 emissions.||13 to 19 Tg C per year||Potential co-benefits such as improved feed efficiency or productivity in livestock.|
|Cropland management practices (Ch. 5, 12)c||Increase in organic residue inputs and soil carbon stocks by reducing tillage and summer fallow, implementing cover cropping, or managing nutrients to increase plant production.|
Reduction in CH4 and nitrous oxide (N2O) emissions by optimizing nitrogen fertilization and water management.
|Soil carbon stock increases of up to 3 megagrams of carbon per hectare; up to 80% reduction in CH4 (especially rice) and N2O, depending on crop, environment, and combination of practices.||Potential co-benefits such as improved soil productivity and lower costs for nitrogen fertilizers.|
Increased organic carbon for improved buffering capacity, water holding capacity, soil fertility, and tilth.
Reduced water use (especially rice).
|Reducing wetland and coastal ecosystem loss (Ch. 13, 15)c||Reduction in emissions by avoiding the loss of wetlands and coastal estuaries.|
Increase in carbon sequestration by restoring drained wetlands, though possibly increasing CH4 emissions.
|Based on the amount of wetlands converted to other land uses in Canada and the United States, restoring all wetland acreage, leading to a gross but highly unrealistic estimate of 43 Tg C per year.||Potential impacts on coastal zone development.|
Increased protection of property from storms.
Reduced export of nutrients to the ocean.
Restored wetlands via improved flood abatement and water quality, but with only about 21% functional compared to functionality of undisturbed sites.
|Urban mitigation (Ch. 4)c||Reduction in city carbon emissions by implementing or improving urban development pathways, building codes, transportation planning, electricity supply, or biotic planning (e.g., tree planting). |
Reduction in CH4 leakage, for example, by upgrading infrastructure.
|Data unavailable for a comprehensive assessment of mitigation potential.||Implications for air quality, urban heat island, and human health, among the many co-effects and priorities for consideration.|
|Increasing bioenergy (Ch. 3)c||Possible reduction or increase in net GHG emissions by substituting biofuel for fossil fuel. Impacts dependent on fuel source and effects on production and consumption cycles.||Estimates of mitigation potential based on life cycle analysis unavailable, though biofuel supply is potentially large.||Increased agricultural commodity prices and land-use changes in other regions, dependent on extent of land supplying the biofuel.|
Increased forest harvesting in response to higher demands for forest biomass, possibly followed by forest area expansion.
a Table includes GHG emissions reductions, carbon stock increases, and avoidance of carbon losses.
b Potential reductions are in addition to baseline.
c Chapter titles—3: Energy Systems; 4: Understanding Urban Carbon Fluxes; 5: Agriculture; 9: Forests; 10: Grasslands; 12: Soils; 13: Terrestrial Wetlands; 15: Tidal Wetlands and Estuaries.
The many land-management options available to reduce net GHG emissions or increase removal of GHGs from the atmosphere (see Table 18.1), taken together, could reduce net emissions by 100 to 500 teragrams of carbon (Tg C) per year, with co-effects becoming highly significant in the high end of this range. Therefore, decisions about land-management policies must take into account the co-effects, which may be positive or negative, along with the potential benefits in terms of reducing GHGs. One of the most significant negative impacts of altering land management to increase carbon storage is a potential reduction in land area devoted to food production if the amount of additional land required exceeds the area of “marginal” (i.e., not productive for crops) land available. On the other hand, positive co-effects may result from management practices that increase soil fertility along with carbon storage, or those that increase protection of water quality or damage from storms and floods.
Although traditionally considered the province of biophysical science, the demand for actionable results has increasingly drawn attention to the need for research from sociology, psychology, and human behavior to inform carbon management. Research in these fields has identified obstacles to effective carbon management, and the approaches to overcome them, at individual to institutional scales (Ross et al., 2016). In researching the interests and understandings held by different actors in Mexico’s program for monitoring, reporting, and verifying (MRV) REDD+, Deschamps Ramírez and Larson (2017) found tension arising from poor understanding of international reporting requirements and the roles and responsibilities of subnational institutions. Weaknesses in understanding and social relations among key institutions limit the effectiveness of carbon management even when decision makers possess and understand strong biophysical analyses (Deschamps Ramírez and Larson 2017). Individuals respond strongly to default options and associated social norms, as demonstrated in comparisons of decisions about whether or not to participate in organ donor programs among different countries. Default settings on furnaces and other appliances to conserve energy, with the option for owners or users to change that setting, could produce widespread behavior shifts and associated changes in carbon emissions (Ross et al., 2016). Efforts to support the capacity of businesses to manage carbon involves research but can fall outside traditional academic frameworks. For example, the Sustainable Purchasing Leadership Council (SPLC) evaluated third-party tools for estimating supplier sustainability across an entire supply base (SPLC 2018). Although these tools focus more broadly than carbon, SPLC’s work summarizing and evaluating them demonstrates the type of collaboration that spurs user-driven science and produces actionable recommendations.
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