The optimal choice of residue management, crop rotations, and cost of carbon sequestration: empirical results in the Midwest US

This study investigates the cost of soil carbon sequestration in the Midwest US. The model addresses several missing components in earlier analyses: the link between the residue level choice and carbon payments, crop rotations, carbon loss when shifting from conservation to conventional tillage and the spatial pattern of carbon sequestration across different soil types. The results suggest that for $100 per metric ton of carbon, 1.5 million metric tons of carbon could be sequestered per year on the 19.9 million hectares of cropland in the study region. These estimates suggest less carbon potential than existing studies because the opportunity costs associated with conservation tillage are fairly high. Annual carbon rental payments are found to be more efficient, as expected, but for smaller programs, per hectare rental payments are not substantially more costly.     

The leaky sink: persistent obstacles to a forest carbon sequestration program based on individual projects

One strategy for mitigating the increase in atmospheric carbon dioxide is to expand the size of the terrestrial carbon sink, particularly forests, essentially using trees as biological scrubbers. Within relevant ranges of carbon abatement targets, augmenting carbon sequestration by protecting and expanding biomass sinks can potentially make large contributions at costs that are comparable or lower than for emission source controls. The Kyoto protocol to the framework convention on climate change includes many provisions for forest and land use carbon sequestration projects and activities in its signatories’ overall greenhouse gas mitigation plans. In particular, the protocol provides a joint implementation provision and a clean development mechanism that would allow nations to claim credit for carbon sequestration projects undertaken in cooperation with other countries. However, there are many obstacles for implementing an effective program of land use change and forestry carbon credits, especially measurement challenges. This paper explains the difficulty that even impartial analysts have in assessing the carbon offset benefits of projects. When these measurement challenges are combined with self-interest, asymmetries of information, and large numbers, it prevents to a project-based forest and land use carbon credit program may be insurmountable.     

The leaky sink: persistent obstacles to a forest carbon sequestration program based on individual projects

Abstract

One strategy for mitigating the increase in atmospheric carbon dioxide is to expand the size of the terrestrial carbon sink, particularly forests, essentially using trees as biological scrubbers. Within relevant ranges of carbon abatement targets, augmenting carbon sequestration by protecting and expanding biomass sinks can potentially make large contributions at costs that are comparable or lower than for emission source controls. The Kyoto protocol to the framework convention on climate change includes many provisions for forest and land use carbon sequestration projects and activities in its signatories' overall greenhouse gas mitigation plans. In particular, the protocol provides a joint implementation provision and a clean development mechanism that would allow nations to claim credit for carbon sequestration projects undertaken in cooperation with other countries. However, there are many obstacles for implementing an effective program of land use change and forestry carbon credits, especially measurement challenges. This paper explains the difficulty that even impartial analysts have in assessing the carbon offset benefits of projects. When these measurement challenges are combined with self-interest, asymmetries of information, and large numbers, it prevents to a project-based forest and land use carbon credit program may be insurmountable.     

Extending timber rotations: carbon and cost implications

A number of studies have suggested that incentives for carbon sequestration could lead to longer rotation periods for even-aged managed forests. In this article we examine the potential costs and quantity of sequestered carbon from extending rotation ages in softwood forests of the southern and western USA. A model of optimal rotations when carbon is a valued asset was developed to show how optimal rotations adjust when carbon is priced. Data on 324 types and site classes of softwood forests in southern and western states of the USA were used to examine the costs of extending rotations. The results were then aggregated by applying the marginal cost curves to inventory data within each county in these states. The results indicate that in these 12 states, about 15 million tCO₂ could be sequestered for less than $7/tCO₂ (1 tCO₂ = 1,000 kg CO₂), although for substantially higher carbon prices of $55/tCO₂, up to 209 million tCO₂ could be sequestered. Timber prices were found to have an important influence on the marginal costs of carbon sequestration, with site quality being of secondary importance. The results also showed that at $55/tCO₂ potentially 1 million ha of softwood forests could be set aside, mostly in the western states.     

Estimating the economic potential for agricultural soil carbon sequestration in the Central United States using an aggregate econometric-process simulation model

The purpose of this paper is to develop and apply a new method to assess economic potential for agricultural greenhouse gas mitigation. This method uses secondary economic data and conventional econometric production models, combined with estimates of soil carbon stocks derived from biophysical simulation models such as Century, to construct economic simulation models that estimate economic potential for carbon sequestration. Using this method, simulations for the central United States show that reduction in fallow and conservation tillage adoption in the wheat-pasture system could generate up to about 1.7 million MgC/yr, whereas increased adoption of conservation tillage in the corn–soy–feed system could generate up to about 6.2 million MgC/yr at a price of $200/MgC. About half of this potential could be achieved at relatively low carbon prices (in the range of $50 per ton). The model used in this analysis produced estimates of economic potential for soil carbon sequestration potential similar to results produced by much more data-intensive, field-scale models, suggesting that this simpler, aggregate modeling approach can produce credible estimates of soil carbon sequestration potential. Carbon rates were found to vary substantially over the region. Using average carbon rates for the region, the model produced carbon sequestration estimates within about 10% of those based on county-specific carbon rates, suggesting that effects of spatial heterogeneity in carbon rates may average out over a large region such as the central United States. However, the average carbon rates produced large prediction errors for individual counties, showing that estimates of carbon rates do need to be matched to the spatial scale of analysis. Transaction costs were found to have a potentially important impact on soil carbon supply at low carbon prices, particularly when carbon rates are low, but this effect diminishes as carbon prices increase. This research was supported in part by the Montana State Agricultural Experiment Station, by the EPA STAR Climate Change program and by the Consortium for the Agricultural Mitigation of Greenhouse Gases. Although the research described in this article has been funded wholly or in part by the United States Environmental Protection Agency through grant R-82874501-0 to Montana State University, it has not been subjected to the Agency’s required peer and policy review and therefore does not necessarily reflect the views of the Agency and no official endorsement should be inferred.     

Cost benefits of forest restoration in a tropical grazing landscape: Thiaki rainforest restoration project

Global forest restoration is vital to mitigate climate change. Tropical forests are under the greatest threat from clearing while offering significant potential for restoration. Forest carbon credits through trading schemes have the potential to enable restoration, providing landholders with incentives to restore forests. Impediments to restoration are numerous, with one of the main ones being the unknown costs of forest restoration and uncertain returns from payment schemes, such as carbon trading programs. Many research and modeling papers on the potential of carbon markets to stimulate reforestation in agricultural landscapes rely on general estimates of reforestation. The reality, though, is that the benefits, returns, and break-even points of the reforestation costs and carbon price are highly sensitive to actual costs. Few papers actually investigate the real costs of farm-level restoration. Nearly all recent papers have used modeled scenarios in calculating Net Present Value (NPV), and so estimates of restoration cost and a return from carbon vary widely depending on modeled assumptions. Real data from a demonstration project in the Wet Tropics of Australia are provided in this paper. Three land use scenarios are compared: carbon only, cattle only, and a combination of carbon and cattle using on-ground data for restoration. Not surprisingly, scenarios of the highest carbon prices generate the highest net benefits in both carbon only and mixed carbon and cattle scenarios. A minimum carbon price of AUD$37 per ton of carbon dioxide equivalent is required to match income derived from cattle. The current policy environment that rewards the lowest cost abatement runs counter to Australia playing its role in the urgent need to limit global temperature rise to 2 degrees Celsius and preferably 1.5 degrees Celsius.     

Potential for forest carbon plantings to offset greenhouse emissions in Australia: economics and constraints to implementation

The theoretical potential for carbon forests to off-set greenhouse gas emissions may be high but the achievable rate is influenced by a range of economic and social factors. Economic returns (net present value, NPV) were calculated spatially across the cleared land area in Australia for ‘environmental carbon plantings’. A total of 105 scenarios were run by varying discount rate, carbon price, rate of carbon sequestration and costs for plantation establishment licenses for water interception. The area for which NPV was positive ranged from zero ha for tightly constrained scenarios to almost the whole of the cleared land (104 M ha) for lower discount rate and highest carbon price. For the most plausible assumptions for cost of establishment and commercial discount rate, no areas were identified as profitable until a carbon price of AUD$40 t CO₂ ^?1 was reached. The many practical constraints to plantation establishment mean that it will likely take decades to have significant impact on emission reductions. Every 1 M ha of carbon forests established would offset about 1.4 % of Australia’s year 2000 emissions (or 7.4 Mt CO₂ year^?1) when an average rate of sequestration per ha was reached. All studies that predict large areas of potentially profitable land for carbon forestry need to be tempered by the realities that constrain land use change. In Australia and globally, carbon plantings can be a useful activity to help mitigate emissions and restore landscapes but it should be viewed as a long-term project in which co-benefits such as biodiversity enhancement can be realised.     

Risk mitigation and the social cost of carbon

The social cost of carbon – i.e., the marginal present-value cost imposed by greenhouse gas emissions – is determined by a complex interaction between factual assumptions, modeling methods, and value judgments. Among the most crucial factors is society's willingness to tolerate potentially catastrophic environmental risks. To explore this issue, the present analysis employs a stochastic climate–economy model that accounts for uncertainties in baseline economic growth, baseline emissions, greenhouse gas mitigation costs, carbon cycling, climate sensitivity, and climate change damages. In this model, preferences are specified to reflect the high degree of risk aversion revealed by private investment decisions, signaled by the large observed gap between the average rates of return paid by safe and risky financial instruments. In contrast, most climate–economy models assume much lower risk aversion. Given high risk aversion, the analysis finds that investment in climate stabilization yields especially large net benefits by forestalling low-probability threats to long-run human well-being. Accordingly, the social cost of carbon attains the markedly high value of $25,700 per metric ton of carbon dioxide in a baseline scenario in which emissions are unregulated. This value falls to just $4 per ton as the stringency of control measures is successively increased. These results cast doubt on the idea that the social cost of carbon takes on a uniquely defined, objective value that is independent of policy decisions. This does not, however, rule out the use of carbon prices to achieve the benefits of climate stabilization using least-cost mitigation measures.     

Soil Carbon Sequestration and the CDM: Opportunities and Challenges for Africa

This paper examines soil carbon sequestration in developing countries in sub-Saharan Africa as part of regional and global attempts to mitigate greenhouse gas emissions and the possibility that the development of greenhouse gas mitigation projects will offer local ancillary benefits. The paper documents the improvements in agricultural practices and land-use management in sub-Saharan Africa that could increase agricultural productivity and sequester soil carbon. During the first five-year commitment period of the Kyoto Protocol, only afforestation and reforestation projects will be eligible for crediting under the Clean Development Mechanism, but soil carbon sequestration and broader sink activities could become eligible during subsequent commitment periods. However, very few cost estimates of soil carbon sequestration strategies exist, and available data are not readily comparable. It is uncertain how large amounts of carbon could be sequestered, and it is unclear how well site-specific studies represent wider areas. It is concluded that there presently is a need to launch long-term (>10 years) field experiments and demonstration and pilot projects for soil carbon sequestration in Africa. It will be important to monitor all environmental effects and carbon `costs' as well as estimate all economic benefits and costs of projects.     

Set-asides for carbon sequestration: implications for permanence and leakage

This paper examines the potential role of forest set-asides in global carbon sequestration policy. While set asides that protect forests from timber harvests and land-use conversion may alleviate concerns with permanence, and they may provide large ancillary environmental benefits, they may also lead to large leakage. This paper uses a global land use and forestry model to examine the efficiency of three crediting schemes for set-asides. The results show that if set-asides are integrated into a global forestry carbon sequestration program that includes a wide range of other management options, then 300 million hectares of land would be set-aside, and up to 128 Pg C could be sequestered in global forests by 2105. Under alternative policies that focus exclusively on set-asides, more forestland can be set-asides, up to 3.2 billion hectare, but these policies invite large leakage in the near-term, and in the long-run, they less net carbon is removed from the atmosphere. Specifically, leakage is estimated to be 47–52%, depending on the policy, and by the end of the century, up to 17% less carbon will be sequestered in all forests.     

Creating Carbon Offsets in Agriculture through No-Till Cultivation: A Meta-Analysis of Costs and Carbon Benefits

Carbon terrestrial sinks are often seen as a low-cost alternative to fuel switching and reduced fossil fuel use for lowering atmospheric CO₂. To determine whether this is true for agriculture, one meta-regression analysis (52 studies, 536 observations) examines the costs of switching from conventional tillage to no-till, while another (51 studies, 374 observations) compares carbon accumulation under the two practices. Costs per ton of carbon uptake are determined by combining the two results. The viability of agricultural carbon sinks is found to vary by region and crop, with no-till representing a low-cost option in some regions (costs of less than $10 per tC), but a high-cost option in others (costs of 100–$400 per tC). A particularly important finding is that no-till cultivation may store no carbon at all if measurements are taken at sufficient depth. In some circumstances no-till cultivation may yield a triple dividend of carbon storage, increased returns and reduced soil erosion, but in many others creating carbon offset credits in agricultural soils is not cost effective because reduced tillage practices store little or no carbon.     

The feasibility of carbon incentives to private forest management in Korea

Forest management is regarded as one possible approach to reducing greenhouse gases by absorbing carbon at a relatively low cost. In Korea, the forest comprises 64% of the total land area, so forests are expected to play a key role in mitigating climate change on the one hand. On the other hand, since 70% of the forest area is owned by the private sector, there is considerable uncertainty about managing forests for the national carbon sink strategy. The objective of this study is to examine the levels of carbon incentives to private forest management for the purpose of maximizing forests’ carbon absorption. First, in the context of present forest management policies, this study discusses applicable measures for the promotion of carbon sequestration in private forests. Next, considering the implications of policies related to forestry, the study develops a hypothetical carbon incentive scheme to compensate for economic revenue loss derived from accepting a rotation period that maximizes carbon sequestration. Carbon incentive levels are estimated by assessing the difference of financial revenue between a financially optimal rotation plan and a carbon-sink maximizing rotation plan. This study found that for red pine forests, the levels of the carbon incentives vary US$2–6 at 5% discount rate and US$ 34–88 at 7% discount rate while the values for oak forests are differing US$2–22 at 5% discount rate and US$ 20–52 at 7% discount rate. The study concludes that the carbon incentive scheme could be effective for increasing the carbon sink. However, given related governmental policies, it may not be desirable to employ the scheme without considering changes in government policy toward land use and regional development.     

Competitiveness of terrestrial greenhouse gas offsets: are they a bridge to the future?

Activities to reduce net greenhouse gas emissions by biological soil or forest carbon sequestration predominantly utilize currently known, readily implementable technologies. Many other greenhouse gas emission reduction options require future technological development or must wait for turnover of capital stock. Carbon sequestration options in soils and forests, while ready to go now, generally have a finite life, allowing use until other strategies are developed. This paper reports on an investigation of the competitiveness of biological carbon sequestration from a dynamic and multiple strategy viewpoint. Key factors affecting the competitiveness of terrestrial mitigation options are land availability and cost effectiveness relative to other options including CO₂ capture and storage, energy efficiency improvements, fuel switching, and non-CO₂ greenhouse gas emission reductions. The analysis results show that, at lower CO₂ prices and in the near term, soil carbon and other agricultural/forestry options can be important bridges to the future, initially providing a substantial portion of attainable reductions in net greenhouse gas emissions, but with a limited role in later years. At higher CO₂ prices, afforestation and biofuels are more dominant among terrestrial options to offset greenhouse gas emissions. But in the longer run, allowing for capital stock turnover, options to reduce greenhouse gas emissions from the energy system and biofuels provide an increasing share of potential reductions in total US greenhouse gas emissions.     

Estimating the value of carbon sequestration ecosystem services in the Mediterranean Sea: An ecological economics approach

Ocean and marine ecosystems provide a range of valuable services to humans, including benefits such as carbon sequestration, whose economic value are as yet poorly understood. This paper presents a novel contribution to the valuation of carbon sequestration services in marine ecosystems with an application to the Mediterranean Sea. We combine a state-of-the-art biogeochemical model with various estimates of the social cost of carbon emissions to provide a spatially explicit characterization of the current flow of values that are attributable to the various sequestration processes, including the biological component. Using conservative estimates of the social cost of carbon, we evaluate the carbon sequestration value flows over the entire basin to range between 127 and 1722 million €/year. Values per unit area range from −135 to 1000 €/km² year, with the exclusive economic zone of some countries acting as net carbon sources. Whereas the contribution of physical processes can be either positive or negative, also depending on the properties of incoming Atlantic water, the contribution of biological processes to the marine “blue carbon” sequestration is always positive, and found to range between 100 to 1500 million €/year for the whole basin.     

Forestry Projects under the Clean Development Mechanism?

Afforestation is considered an important option for mitigation of greenhousegas emissions. Recently, plantation projects have been suggested for inclusionunder the Clean Development Mechanism. While considered a cheap option,significant uncertainties make it difficult to determine the (net) carbonbenefits and profitability of forestry projects. The current uncertaintiesabout the regulatory framework of the CDM and the environmental and economicperformance of plantation forestry could create uncertainties with respect tothe additionality of such projects and thus their acceptance under themechanism.Six plantation forestry projects that were proposed in Brazil have been usedas cases to study sources of uncertainty for carbon benefits and economics forsuch projects. These cases vary widely in terms of productivity and productsdelivered. A quantitative model for calculating greenhouse gas balances andfinancial benefits and costs, taking a broad range of variables into account,was developed. Data from the developers of the proposed projects was used asmain source material. Subsequently, scenario's were evaluated, containingdifferent and realistic options for baseline vegetation, carbon creditingsystems and CDM modalities, fluctuations in product prices, discount rates andcarbon prices.The real cost of combined carbon sequestration and substitution for the caseprojects was below $3 per ton of carbon avoided, when based exclusivelyon data supplied by project developers. However, potential variations incarbon impact and costs based on scenario options were very large. Differentbaseline vegetation or adopting a different discount rate cause carbon creditsto vary by as much as an order of magnitude. Different carbon crediting systemsor fluctuations in (commodity) product prices cause variations up to200% in carbon credits and NPV. This makes the additionality of suchprojects difficult to determine. Five of the six case projects seem uneligiblefor development under the CDM. A critical attitude towards the use ofplantation projects under the CDM seems justified.     

An Overview of Terrestrial Sequestration of Carbon Dioxide: the United States Department of Energy's Fossil Energy R&D Program

Increasing concentrations of CO₂ and other greenhouse gases (GHG) in the Earth's atmosphere have the potential to enhance the natural greenhouse effect, which may result in climatic changes. The main anthropogenic contributors to this increase are fossil fuel combustion, land use conversion, and soil cultivation. It is clear that overcoming the challenge of global climate change will require a combination of approaches, including increased energy efficiency, energy conservation, alternative energy sources, and carbon (C) capture and sequestration. The United States Department of Energy (DOE) is sponsoring the development of new technologies that can provide energy and promote economic prosperity while reducing GHG emissions. One option that can contribute to achieving this goal is the capture and sequestration of CO₂ in geologic formations. An alternative approach is C sequestration in terrestrial ecosystsems through natural processes. Enhancing such natural pools (known as natural sequestration) can make a significant contribution to CO₂ management strategies with the potential to sequester about 290 Tg C/y in U.S. soils. In addition to soils, there is also a large potential for C sequestration in above and belowground biomass in forest ecosystems.A major area of interest to DOE's fossil energy program is reclaimed mined lands, of which there may be 0.63 ×10⁶ ha in the U.S. These areas are essentially devoid of soil C; therefore, they provide an excellent opportunity to sequester C in both soils and vegetation. Measurement of C in these ecosystems requires the development of new technology and protocols that are accurate and economically viable. Field demonstrations are needed to accurately determine C sequestration potential and to demonstrate the ecological and aesthetic benefits in improved soil and water quality, increased biodiversity, and restored ecosystems.The DOE's research program in natural sequestration highlights fundamental and applied studies, such as the development of measurement, monitoring, and verification technologies and protocols and field tests aimed at developing techniques for maximizing the productivity of hitherto infertile soils and degraded ecosystems.     

Designing policies to mitigate the agricultural contribution to climate change: an assessment of soil based carbon sequestration and its ancillary effects

Soil carbon sequestration has been regarded as a cheap and cost-effective way to sequester carbon until other technologies to tackle climate change become available or more cost-effective. An assessment of the social desirability of a soil carbon sequestration policy requires the consideration of all associated social costs and benefits. Measures to re-accumulate carbon in soils have ancillary or co-effects on the environment that can be beneficial or detrimental to social welfare and few of which are traded in markets. This paper discusses issues related to the development of soil carbon sequestration policies into agri-environmental schemes and reports findings from an application of a choice experiment to elicit preferences and estimate benefits of a soil carbon programme in Scotland under consideration of co-effects on biodiversity and rural viability. Preferences for soil carbon based mitigation are found to be heterogeneous and related to beliefs about climate change and attitudes towards its mitigation. Benefit estimates suggest that including co-effects can significantly change the outcome of cost?Cbenefit tests. Implications for the development of climate change policies are discussed.     

Greenhouse gas taxes on animal food products: rationale, tax scheme and climate mitigation effects

Agriculture is responsible for 25?C30% of global anthropogenic greenhouse gas (GHG) emissions but has thus far been largely exempted from climate policies. Because of high monitoring costs and comparatively low technical potential for emission reductions in the agricultural sector, output taxes on emission-intensive agricultural goods may be an efficient policy instrument to deal with agricultural GHG emissions. In this study we assess the emission mitigation potential of GHG weighted consumption taxes on animal food products in the EU. We also estimate the decrease in agricultural land area through the related changes in food production and the additional mitigation potential in devoting this land to bioenergy production. Estimates are based on a model of food consumption and the related land use and GHG emissions in the EU. Results indicate that agricultural emissions in the EU27 can be reduced by approximately 32 million tons of CO₂-eq with a GHG weighted tax on animal food products corresponding to ?60 per ton CO₂-eq. The effect of the tax is estimated to be six times higher if lignocellulosic crops are grown on the land made available and used to substitute for coal in power generation. Most of the effect of a GHG weighted tax on animal food can be captured by taxing the consumption of ruminant meat alone.     

Incorporating blue carbon sequestration benefits into sub-national climate policies

The emissions reduction pledges made by individual countries through the 2015 Paris Agreement represent the current global commitment to mitigate greenhouse gas emissions in the face of the enduring climate crisis. Natural lands carbon sequestration and storage are critical for successful pathways to global decarbonization (i.e., as a negative emissions technology). Coastal vegetated habitats maintain carbon sequestration rates exceeding forest sequestration rates on a per unit area basis by nearly two orders of magnitude. These blue carbon habitats and their associated carbon sequestration benefits are vulnerable to losses from land-use change and sea-level rise. Incorporation of blue carbon habitats in climate change policy is one strategy for both maintaining these habitats and conserving significant carbon sequestration capabilities. Previous policy assessments have found the potential for incorporation of coastal carbon sequestration in national-level policies, yet there has – to date – been little inclusion of blue carbon in the national-scale implementation of Paris commitments. Recently, sub-national jurisdictions have gained attention as models for pathways to decarbonization. However, few previous studies have examined sub-national level policy opportunities for operationalizing blue carbon into climate decision-making. California is uniquely poised to integrate benefits from blue carbon into its coastal planning and management and its suite of climate mitigation policies. Here, we evaluated legal authorities and policy contexts addressing sequestration specifically from blue carbon habitats. We synthesized the progressive action in California’s approaches to mitigate carbon emissions including statutory, regulatory, and non-regulatory opportunities to incorporate blue carbon ecosystem service information into state- and local-level management decisions. To illustrate how actionable blue carbon information can be produced for use in decision-making, we conducted a spatial analysis of blue carbon sequestration in several locations in California across multiple agencies and management contexts. We found that the average market values of carbon sequestration services in 2100 ranged from $7,730 to $44,000 per hectare and that the social cost of carbon sequestration value was 1.3 to 2.7 times the market value. We also demonstrated that restoration of small areas with high sequestration rates can be comparable to the sequestration of existing marshes. Our results illustrate how accessible information about carbon sequestration in coastal habitats can be directly incorporated into existing policy frameworks at the sub-national scale. The incorporation of blue carbon sequestration benefits into sub-national climate policies can serve as a model for the development of future policy approaches for negative emissions technologies, with consequences for the success of the Paris Agreement and science-based decarbonization by mid-century.     

Climate change adaptation cost in the US: what do we know?

Researchers and policy makers increasingly recognize the need to adapt to future changes in climate, given that past emissions of greenhouse gases have already committed the world to some level of climate change. However, the current understanding of the costs and benefits of adaptation measures is still fairly rudimentary, and far from comprehensive. An assessment is presented of the current state of knowledge on the magnitude of adaptation costs in the United States. While incomplete, the studies suggest that adaptation cost could be as high as tens or hundreds of billions of dollars per year by the middle of this century. Key studies are identified in each sector, and the cost estimates and approaches to cost estimation are surveyed. Methodological issues are highlighted in interpreting, comparing, and aggregating adaptation cost estimates. Policy recommendations are made along with appropriate steps to make future adaptation cost studies more comparable within and across sectors and more accessible and relevant to policy and decision makers.

Policy relevance

Designing and implementing climate change adaptation policy requires good information about the effectiveness and cost of available adaptive options. The current state of knowledge on adaptation costs in the United States is assessed and significant gaps in the literature are highlighted – particularly in terms of sectoral and geographic coverage – as well as inconsistencies in methodologies and assumptions that hamper comparison across studies. Critical steps are identified that can be taken to make adaptation cost studies more accessible and useful to decision makers. The findings and recommendations are relevant to adaptation cost studies globally, not just in the United States.