The western North American forestland carbon sink: will our climate commitments go up in smoke?

Climate change is a complex and contentious public issue, but the risk-management options available to us are straightforward and have well-characterized strengths and weaknesses.

Operationalizing marketable blue carbon

We review science‐based adaptation strategies for western North American (wNA) forests that include restoring active fire regimes and fostering resilient structure and composition of forested landscapes. As part of the review, we address common questions associated with climate adaptation and realignment treatments that run counter to a broad consensus in the literature. These include the following: (1) Are the effects of fire exclusion overstated? If so, are treatments unwarranted and even counterproductive? (2) Is forest thinning alone sufficient to mitigate wildfire hazard? (3) Can forest thinning and prescribed burning solve the problem? (4) Should active forest management, including forest thinning, be concentrated in the wildland urban interface (WUI)? (5) Can wildfires on their own do the work of fuel treatments? (6) Is the primary objective of fuel reduction treatments to assist in future firefighting response and containment? (7) Do fuel treatments work under extreme fire weather? (8) Is the scale of the problem too great? Can we ever catch up? (9) Will planting more trees mitigate climate change in wNA forests? And (10) is post‐fire management needed or even ecologically justified? Based on our review of the scientific evidence, a range of proactive management actions are justified and necessary to keep pace with changing climatic and wildfire regimes and declining forest heterogeneity after severe wildfires. Science‐based adaptation options include the use of managed wildfire, prescribed burning, and coupled mechanical thinning and prescribed burning as is consistent with land management allocations and forest conditions. Although some current models of fire management in wNA are averse to short‐term risks and uncertainties, the long‐term environmental, social, and cultural consequences of wildfire management primarily grounded in fire suppression are well documented, highlighting an urgency to invest in intentional forest management and restoration of active fire regimes.

BackgroundHistorically, reburn dynamics from cultural and lightning ignitions were central to the ecology of fire in the western United States (wUS), whereby past fire effects limited future fire growth and severity. Over millennia, reburns created heterogenous patchworks of vegetation and fuels that provided avenues and impediments to the flow of future fires, and feedbacks to future fire event sizes and their severity patterns. These dynamics have been significantly altered after more than a century of settler colonization, fire exclusion, and past forest management, now compounded by rapid climatic warming. Under climate change, the area impacted by large and severe wildfires will likely increase — with further implications for self-regulating properties of affected systems. An in-depth understanding of the ecology of reburns and their influence on system-level dynamics provides a baseline for understanding current and future landscape fire-vegetation interactions.ResultsHere, we present a detailed characterization of REBURN — a geospatial modeling framework designed to simulate reburn dynamics over large areas and long time frames. We interpret fire-vegetation dynamics for a large testbed landscape in eastern Washington State, USA. The landscape is comprised of common temperate forest and nonforest vegetation types distributed along broad topo-edaphic gradients. Each pixel in a vegetation type is represented by a pathway group (PWG), which assigns a specific state-transition model (STM) based on that pixel’s biophysical setting. STMs represent daily simulated and annually summarized vegetation and fuel succession, and wildfire effects on forest and nonforest succession. Wildfire dynamics are driven by annual ignitions, fire weather and topographic conditions, and annual vegetation and fuel successional states of burned and unburned pixels.ConclusionsOur simulation study is the first to evaluate how fire exclusion and forest management altered the active fire regime of this landscape, its surface and canopy fuel patterns, forest and nonforest structural conditions, and the dynamics of forest reburning. The REBURN framework is now being used in related studies to evaluate future climate change scenarios and compare the efficacy of fire and fuel management strategies that either enable the return of active fire regimes or depend on fire suppression and wildfire effects on forest burning.

IntroductionGlobal climate change, increase in human activities, and prominence of ecological issues have led to uneven quantitative and spatial distributions of carbon emission and sequestration of terrestrial ecosystems. Such uneven distributions can lead to more negative impacts on the natural environment and human living conditions.MethodsTherefore, based on the carbon neutralization policy, we conducted geographically weighted regression (GWR) modeling in this study using panel data from 352 Chinese prefectural administrative districts in 2000, 2005, 2010, and 2017 to analyze and determine the impact factors and their spatial distribution for carbon emission and sequestration of terrestrial ecosystems.ResultsOur results showed that total population (TP), per capita gross domestic product (GDP) (PCG), proportion of secondary industry output (PSIO), scale of urban built-up area (SUB), green space proportion in city areas (GSP), normalized difference vegetation index (NDVI), and temperature (TEM) are factors driving carbon sequestration and carbon emission. The spatial distribution of these driving factors in mainland China is: (1) TP showed a negative correlation to carbon emission in most areas, while it exhibited a positive correlation to carbon sequestration in the southern, southwestern, and western parts of northwest China; however, in all other areas, TP showed a negative correlation with carbon sequestration; (2) PCG was positively correlated to carbon emission in most areas of China and to carbon sequestration in southwest, south, central, and northeast China; however, PCG demonstrated a negative correlation to carbon sequestration in the remaining areas; (3) PSIO and SUB presented a positive correlation to carbon emission and a negative correlation to carbon sequestration in most areas; (3) In contrast, GSP showed a negative correlation to carbon emission and a positive correlation to carbon sequestration in most areas; (5)NDVI showed a negative correlation to carbon emission and carbon sequestration in most areas toward the east of the “Heihe-Tengchong Line”; NDVI was positively correlated to both carbon emission and sequestration toward the west of this line; (6)TEM was positively correlated to carbon emission and sequestration in most parts of China.DiscussionBased on these results, we further divided the Chinese cities into 6 groups: (1) Groups 1, 2, 3, and 6 are areas where carbon emission and sequestration are governed by both socioeconomic and natural ecological factors. The major driving factors of carbon emission and carbon sequestration in group 1 are PSIO, GSP, and NDVI; the driving factors of group 2 are SUB and NDVI. Meanwhile, carbon emission and sequestration in group 3 are governed by PCG, GSP, and NDVI; for group 6, carbon emission and sequestration are controlled by PCG, SUB, GSP, and NDVI; (2) Group 4 represents areas where carbon emission and sequestration are majorly impacted by PCG and SUB, thereby rendering socioeconomic factors as the major driving forces. Group 5 represents areas where carbon emission and sequestration are sensitive to the natural environment, with GSP and NDVI being the driving factors. Considering the uneven distribution of carbon sequestration and emission and the diverse driving factors in different areas of China, we provided guidance for future environmental policies aimed at reducing the uneven distribution of carbon sequestration and emission in different areas to achieve carbon neutralization.

Urban and peri-urban agriculture under climate change: A review on carbon emissions and sequestration

The scientific community agrees that climate change is happening, is largely human induced, and will have serious consequences for human health (Field and others 2014). The health consequences of climate variability and change are diverse, potentially affecting the burden of a wide range of health outcomes. Changing weather patterns can affect the magnitude and pattern of morbidity and mortality from extreme weather and climate events, and from changing concentrations of ozone, particulate matter, and aeroallergens (Smith and others 2014). Changing weather patterns and climatic shifts may also create environmental conditions that facilitate alterations in the geographic range, seasonality, and incidence of some infectious diseases in some regions, such as the spread of malaria into highland areas in parts of Sub-Saharan Africa. Changes in water availability and agricultural productivity could affect undernutrition, particularly in some parts of Africa and Asia (Lloyd, Kovats, and Chalabi 2011). Although climate change will likely increase positive health outcomes in some regions, the overall balance will be detrimental for health and well-being, especially in low- and lower-middle-income countries that experience higher burdens of climate-sensitive health outcomes (Smith and others 2014).The pathways between climate change and health outcomes are often complex and indirect, making attribution challenging. Climate change may not be the most important driver of climate-sensitive health outcomes over the next few decades but could be significant past the middle of this century. Climate change is a stress multiplier, putting pressure on vulnerable systems, populations, and regions. For example, temperature is associated with the incidence of some food- and water-borne diseases that are significant sources of childhood mortality (Smith and others 2014). Reducing the burden of these diseases requires improved access to safe water and improved sanitation. Poverty is a primary driver underlying the health risks of climate change (Smith and others 2014). Poverty alleviation programs could improve the capacity of health systems to manage risks and reduce the overall costs of a changing climate.Climate change entails other unique challenges:Significant reductions in greenhouse gas emissions (mitigation) in the next few years will be critical to preventing more severe climate change later in the century, but they will have limited effects on weather patterns in the short term. In terms of costing, another complexity is that these policies and technologies are associated with short-term health benefits (Garcia-Menendez and others 2015).Reducing and managing health risks over the next few decades will require modifying health systems to prepare for, cope with, and recover from the health consequences of climate variability and change; these changes are part of what is termed adaptation. Adaptation will be required across the century, with the extent of mitigation being a key determinant of health systems’ ability to manage risks projected later in the century (Smith and others 2014). No matter the success of adaptation and mitigation, residual risks from climate change will burden health systems, particularly in low- and middle-income countries (LMICs).Given these complexities, estimating the costs of managing the health risks of climate variability and change is not straightforward. The wide range of health outcomes potentially affected means counting (1) costs associated with increased health care and public health interventions for morbidity and mortality from a long list of climate-sensitive health outcomes; (2) costs associated with lost work days and lower productivity; and (3) costs associated with well-being. Costs could also accrue from repeated episodes of malaria, diarrhea, or other infectious diseases that affect childhood development and health in later life. Costs associated with actions taken in other sectors are also important for health, such as access to safe water and improved sanitation. A portion of the costs of managing the health risks associated with migrants and environmental refugees could be, but has not been, counted.Further, costs and benefits will be displaced over time, with costs associated with increased health burdens occurring now because of past greenhouse gas emissions and benefits occurring later in the century because of mitigation implemented in the next few years. A few preliminary estimates have been made of the costs of adaptation. However, more work is needed to understand how climate variability and change could affect the ability of health systems to manage risks over long temporal scales.This chapter reviews the health risks of climate variability and change, discusses key components of those risks, summarizes the attributes of climate-resilient health systems, provides an overview of the costs of increasing health resilience that arise from other sectors, reviews temporal and spatial scale issues, and summarizes key conclusions regarding the costs of the health risks of climate change.

Better information on greenhouse gas (GHG) emissions and mitigation potential in the agricultural sector is necessary to manage these emissions and identify responses that are consistent with the food security and economic development priorities of countries. Critical activity data (what crops or livestock are managed in what way) are poor or lacking for many agricultural systems, especially in developing countries. In addition, the currently available methods for quantifying emissions and mitigation are often too expensive or complex or not sufficiently user friendly for widespread use.The purpose of this focus issue is to capture the state of the art in quantifying greenhouse gases from agricultural systems, with the goal of better understanding our current capabilities and near-term potential for improvement, with particular attention to quantification issues relevant to smallholders in developing countries. This work is timely in light of international discussions and negotiations around how agriculture should be included in efforts to reduce and adapt to climate change impacts, and considering that significant climate financing to developing countries in post-2012 agreements may be linked to their increased ability to identify and report GHG emissions (Murphy et al 2010, CCAFS 2011, FAO 2011).

Taking Stock of Strategies on Climate Change and the Way Forward: A Strategic Climate Change Framework for Australia

We investigated how climate change affects the diameter growth of boreal Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies (L.) H. Karst.), and silver birch (Betula pendula Roth) at varying temporal and spatial scales. We generated data with a gap-type ecosystem model for selected locations and sites throughout Finland. In simulations, we used the current climate and recent-generation (CMIP5) global climate model projections under three representative concentration pathways (RCPs) forcing scenarios for the period 2010–2099. Based on this data, we developed diameter growth response functions to identify the growth responses of forests under mild (RCP2.6), moderate (RCP4.5), and severe (RCP8.5) climate change at varying temporal and spatial scales. Climate change may increase growth primarily in the north, with a clearly larger effect on birch and Scots pine than Norway spruce. In the south, the growth of Norway spruce may decrease largely under moderate and severe climate change, in contrast to that of birch. The growth of Scots pine may also decrease slightly under severe climate change. The degree of differences between tree species and regions may increase along with the severity of climate change. Appropriate site-specific use of tree species may sustain forest productivity under climate change. Growth response functions, like we developed, provide novel means to take account of climate change in empirical growth and yield models, which as such include no climate change for forest calculations.

The Parties to the United Nations Framework Convention on Climate Change (UNFCCC) continue their efforts to forge a new binding international agreement by 2015. The negotiations face daunting odds, but the 2009 Copenhagen Accord's shift towards heterogeneous national commitments was a positive step forward for climate policy. The prior presumption that binding commitments could only take the form of a percentage reduction relative to historical levels alienated rapidly industrializing countries and led to unproductive disputes over base years and other issues of target formulation. However, the disparate approaches now under discussion complicate comparing the likely emissions reductions and economic efforts required to achieve the commitments. This paper makes two points. First, we offer good reasons and ways to adapt international negotiations to allow for price-based commitments. The economic uncertainty surrounding target-only commitments is enormous. Combining a clear cumulative emissions target with limits on the cost associated with achieving the target would balance the environmental objective with the need to ensure that commitments remain feasible. This economic insurance could foster greater participation in the agreement and more ambitious commitments. Specifically, we suggest that in addition to their cumulative emissions targets for the 2013 to 2020 period, major economies could agree to a price collar on greenhouse gas emissions in their domestic economies. This would include starting floor and ceiling prices on a ton of CO2 and a schedule for real increases in those prices. All major parties would need to show at least a minimum level of effort regardless of whether they achieve their emissions target, and they would be allowed to exceed their target if they are unable to achieve it in spite of undertaking a high level of effort. The paper provides an example of how a price collar would work in the US context under a cap-and-trade system. Second, analyzing proposed climate commitments in terms of their implied economic stringency, as measured by the implied price on carbon necessary to achieve the targets, offers transparent and verifiable assurance of the comparability of effort across countries. It possible to calculate carbon price equivalents of climate commitments in a conceptually similar way to the tariff equivalents used in international trade negotiations. In sum, the lack of transparency in the level of effort involved in achieving particular emissions targets highlights the potential value of allowing for price-based commitments and argues for greater economic transparency in the international negotiation process.

Climate Resilient Villages for Sustainable Food Security in Tropical India: Concept, Process, Technologies, Institutions, and Impacts

Nature‐based Solutions to tackle climate change and restore biodiversity

Greenhouse gas reduction and carbon sequestration are crucial strategies for addressing climate change. However, extreme weather events such as heavy rainfall and typhoons trigger soil erosion and landslides that severely impact the environment. These events not only release substantial greenhouse gases into the atmosphere and water bodies through large-scale collapses but also significantly delay ecosystem recovery and carbon sequestration processes. As climate change intensifies, the potential benefits of soil and water conservation engineering in mitigating greenhouse gas emissions and enhancing carbon sinks have gained increasing attention. Check dams, as one of the key engineering structures for stabilizing sediment and preventing slope disasters, play a vital role in preventing large-scale landslides. While research on sediment stabilization mechanisms of check dams is well-established, studies on their organic carbon sequestration benefits remain limited. In particular, the temporal dynamics of carbon mechanisms are not well understood, making it difficult to provide solid scientific evidence for the carbon sequestration benefits of check dams.This study uses precipitation events as a baseline to investigate the effects of check dam engineering on soil carbon sequestration and explores the mechanisms of carbon flow and sequestration from watershed soil erosion to sediment deposition within check dams. The research methodology involves selecting watersheds with fragile geology susceptible to erosion for sample collection and analysis. By examining changes in sediment organic carbon content before and after precipitation events, we analyze the transformation and sequestration mechanisms of organic carbon during erosion and deposition processes. Furthermore, through precipitation event simulations, we quantify soil erosion rates in watersheds and assess carbon loss and retention during sediment deposition in check dams to establish a simple and feasible method for sampling and carbon sequestration calculation.The study aims to reveal the carbon sequestration benefits of check dams during sediment stabilization processes and, through baseline establishment, develop an economical and scientific method for estimating carbon sequestration capacity. This method can be applied to large-scale assessments of carbon sequestration benefits of check dam projects across different regions, providing new scientific perspectives and empirical evidence for the role of soil and water conservation engineering in climate change mitigation. This research not only helps deepen our understanding of the carbon sequestration benefits of check dams but also provides crucial references for policy formulation and engineering planning, further promoting the integration and implementation of climate change adaptation and mitigation strategies.Keywords: Check dam, Carbon sequestration, Watershed management, Soil erosion

Forests have a prominent role in carbon sequestration and storage. Climate change and anthropogenic forcing have altered the dominant characteristics of some forested ecosystems through changes to their disturbance regimes, particularly fire. Ecosystems that historically burned frequently, like pinelands in the southeastern United States, risk changes in their structure and function when the fire regime they require is altered. Although the carbon storage potential in an unburned southeastern U.S. forest would be larger, this scenario is unrealistic due to the likelihood of wildfire. Additionally, fire exclusion can have negative consequences on these forests health, biodiversity, and species endemism. There is a need, specifically for the southeast, to estimate carbon and species dynamics based on the differences between various fire regimes, and particularly the differences between prescribed fire and wildfire. These are important factors to consider given that prescribed fire is a common tool used in the southeast, and wildfires are ever more present. Field data from an experimentalPinus palustris(longleaf pine) forest of southwest Georgia were used to parametrize the forest landscape modelLANDIS‐II. The model simulated how carbon and species dynamics differ under a fire exclusion, a prescribed fire, and multiple wildfire scenarios. All scenarios except fire exclusion resulted in net emissions to the atmosphere, but prescribed fire produced the least carbon emissions from fire and maintained the most stable aboveground biomass compared to wildfire scenarios. Removing fire for approximately a century was necessary to obtain an average stand‐level biomass greater than that of prescribed fire and net emissions less than that of prescribed fire. The prescribed fire scenario produced a longleaf pine‐dominated forest, the exclusion scenario converted to predominantly oak speciesQuercus virginiana(live oak),Q. stellata(post oak), andQ. margaretta(sand post oak), while scenarios with intermediate wildfire regimes supported a mix of other fire‐facilitator hardwoods and pine species, such asQ. incana(bluejack oak) andPinus elliotti(slash pine). Overall, this study supports prescribed fire regimes in southeastern U.S. pinelands to both minimize carbon emissions and preserve native biodiversity.