People expect land to provide a solid and permanent footing for infrastructure, public safety, and the built environment. Climate change threatens this in numerous ways, including increases in erosion, permafrost thaw, slope failure, fire, flooding, and shoreline retreat. Land-use changes themselves can interact with these climate impacts in complex ways (KM 6.2).
As sea levels rise, coastal infrastructure is increasingly exposed to risks of flooding and wave action from storm surges and nuisance flooding during high tides, with low-income coastal communities facing greater risks due to fewer resources for response (KMs 9.2, 23.1). The Atlantic and Gulf Coasts are particularly vulnerable to high tide flooding.9 Decadal-scale variability in Great Lakes water levels drives shoreline erosion (KM 24.5). Increases in the magnitude and frequency of heavy rain in a warmer climate heighten the risk of damage from river flooding, especially where infrastructure for water storage, treatment, and transfer becomes overwhelmed. Increased storm rainfall puts roads and buildings at greater risk of damage by landslides.10 For example, Hurricane Maria, a Category 4 storm in 2017, caused substantial damage and fatalities in Puerto Rico, as well as more than 70,000 landslides.11
Warming of colder regions such as Alaska presents significant risks. Damage to roads and the Trans-Alaska Pipeline System is occurring due to ground destabilization as permafrost thaws.12,13 As steep, rocky terrain warms and thaws, rockfalls can increase,14 and as tidewater glaciers retreat, newly destabilized slopes in front of glaciers can collapse into water, causing potentially hazardous tsunamis.15,16
The USGS17 provides emergency assessment of postfire debris-flow hazards (Focus on Western Wildfires). Fire and postfire debris flows increasingly threaten infrastructure and public safety as a warming climate and increased drought raise the risk of large, intense fires.18,19,20,21 Notable among recent examples was the debris flow following the Thomas Fire in Southern California, which killed 23 people, damaged 558 structures, closed a major highway for 13 days, and caused more than $1.15 billion in damages (in 2022 dollars; Figure 6.5).22,23 Risks to water supply and quality continue for years after a fire, as erosion washes excess sediment and pollutants downstream,24 shortening the lifespan of water-storage reservoirs.24,25,26 Sediment production is projected to double in one-third of western US watersheds by 2050 due to increased fire and extreme rain.26
The Southwest faces additional challenges to infrastructure and public health and safety from increased airborne dust,27,28,29 which can carry human disease and result in traffic accidents.30,31 Vegetation loss during drought can cause marginally stable land to transition to actively migrating sand dunes, some of which damage buildings and roads.32,33
Land provides essential services by supporting the production of food for people, feed for animals, and forage for wildlife. Climate change has led to increased extremes of both temperature and precipitation, with increased risks to crop yield (KM 11.2) and associated impacts on land-cover and land-use change (LCLUC). Crop yields in the US continue to increase but are subject to large year-to-year fluctuations driven by environmental stresses34,35 and have become increasingly sensitive to water availability over the past two decades.36 Yield loss associated with warming has resulted primarily from drought, with heat stress playing a secondary role.37 Flooding also causes crop damage; during 1981–2016 in the US, inundation-induced yield loss was comparable in magnitude to that caused by extreme drought.38
In arid and semiarid lands of the Southwest, livestock overgrazing, oil and gas extraction, and off-road vehicle use amplify the effects of warming39 by damaging vegetation and biological soil crusts,40 further increasing dust production. The spread of invasive plants exacerbates this transition, leaving landscapes less adaptable to warming.41 Water extraction by humans lowers water tables, stressing plants, drying lakebeds, and increasing dust production. These factors, together with the warming-induced drought, reduce the productivity and carrying capacity of US rangelands (KM 28.3).
Forests provide critical value to society by supplying a wide range of wood products, protecting water quality, supporting biodiversity, and providing recreational opportunities and spiritual and cultural benefits. Forest land cover can reduce warming locally by providing increased evaporation and shade.42 The effects of land-use change on forest goods and services, including the value of biodiversity, are still being explored.43,44,45 In some cases, forest management can increase biodiversity and offset regional losses due to urbanization, but future losses of biodiversity due to climate change may be greater than reforestation offsets.46
Multiple interacting factors drive changes in goods and services from forest lands, including development, abandonment and expansion of agricultural land, and incentives for reforestation and conservation.47 Mixed land uses such as agroforestry are expected to increase soil water infiltration compared to agriculture alone, providing protection against warming, drought, and soil erosion due to overland flow during extreme precipitation events.48 Forest land-use transitions intended to mitigate climate change must be carefully assessed to prevent unintended consequences, such as net losses of carbon, biodiversity, habitat, soil quality, or other ecosystem services when converting mature forest to bioenergy crop cultivation (e.g., Harper et al. 201849).
Land ecosystems provide an important service to society by sequestering a fraction of the carbon emitted to the atmosphere through fossil fuel combustion and land use. The net carbon balance at any location is the result of multiple simultaneous losses and gains related to plant growth and organic matter decomposition (KM 8.1), historical and current LCLUC, and climate conditions including atmospheric carbon dioxide (CO2) concentration and local rates of nitrogen deposition (Figure 6.6).50 Northern Hemisphere forests are important carbon sinks (KM 7.1).51 Boreal and tropical forests are both globally important carbon sinks, and since 1992 the boreal forest sink has been increasing in importance relative to the tropical forest sink.52 Other ecosystems, such as grasslands,53 wetlands,54 and some agricultural systems (KM 11.1)55 also contribute to the carbon sink, with complex and uncertain interactions with management actions.
While highly variable from year to year, the fraction of emissions taken up by land ecosystems has remained relatively stable on decadal timescales (Box 7.2). Recent evidence suggests that plant response to increasing atmospheric CO2 is the dominant factor driving the land carbon sink at global scales.56,57 A significant part of the land sink is also attributed to recovery following natural disturbances and legacy effects of past LCLUC.58,59,60,61
Impacts of climate change are transforming landscapes in ways considered intrinsically detrimental. Communities with especially strong ties to place and local ecosystems, including but not limited to Tribal and Indigenous groups, may suffer declining cultural and spiritual connections with the land through these changes (KM 15.2),62 such as through the drying of formerly perennial springs and streams that have spiritual significance63 or through reduced opportunities for traditional harvesting of plants that decline as environmental conditions change. In central and northern Alaska, traditional methods of hunting on sea ice have become less feasible, and destabilization of thawing permafrost jeopardizes long-occupied communities (KM 29.3).64,65 Subsistence and recreational fishing are reduced by ecosystem changes, some of which are climate driven and will worsen with additional warming;66 for example, decreased salmon abundance has profound negative effects on many Tribes in the Northwest (KM 27.1).67 Other recreational land uses are limited by the changing seasonality of river flows, loss of ice and snow, and loss of access to areas recently burned.
Ecosystem resilience—defined here as the capacity of a land system to respond to disturbance by resisting damage and/or recovering quickly, maintaining its essential structure and function—determines the persistence of services amid LCLUC. Disturbance is defined here as any discrete event (e.g., fire, flooding, drought, wind, geological hazard, pathogen, insect infestation, etc.) that occurs outside the range of natural variability (e.g., vegetation phenology, climate interannual variability, etc.) of the land system.68 Management also impacts land systems, with the potential to both increase or decrease resilience. Resilience enables natural and built systems to maintain the continued delivery of goods and services in the face of changes. Climate change is affecting ecosystem resilience, triggering responses such as shifted distribution of species and reduced biodiversity (KM 8.2),69,70 changed timing of biological processes,71,72 altered success of existing land uses,73,74 and lowered ability of systems to resist and recover from land-use activities and natural disturbance.75 Ecosystems in the US have experienced increases in average temperature and extreme heat,76 increased drought,77 and increased intensity and frequency of extreme precipitation.78,79 Changes in precipitation characteristics and warming have driven an increase in aridity in much of the United States,80,81 with lasting impacts on ecosystems.82 Land use and management affect ecosystem resilience and interact with climate change to determine the structure and function of the land system (KM 20.3).83,84 The fact that human decisions can influence resilience provides opportunities for climate mitigation (Ch. 31) and adaptation (KM 6.3; Ch. 32) and is a foundation for nature-based solutions to climate change,85 as well as an opportunity to improve resilience through management actions informed by Indigenous Knowledge (KM 16.2).86
Climate change and land use individually and interactively affect land systems, the services they provide to humans, and the resilience of ecosystems. Climate change alters landscape characteristics and management outcomes, which drive changes in land use and/or land cover (Figure 6.7). Land use itself impacts the land system, with potential to both increase and decrease resilience. Land use and land cover help determine climate via effects on carbon, water, and energy exchange with the atmosphere.
Climate change affects ecosystem resilience, structure, and function. For example, tree mortality events have resulted from drought and/or high temperatures in the temperate and boreal forests of western North America,87,88 and widespread death of many tree species has been linked to climate change through wildfire and insect attack.89,90 Warming-induced drought is causing widespread mortality of forests in the Southwest US.91 Increased tree mortality and impaired regeneration decrease the resilience of forests (KM 7.1).92,93
Increases in average temperature and altered precipitation patterns cause changes in species composition,92,93 such as encroachment of shrubs into grasslands94 and invasion by exotic grasses into rangelands, drylands, and forests.41,95 Exotic grass invasion increases fuel loads and the ability of fire to move across the landscape, often resulting in large increases in fire risk.41,96,97 By reducing fuel moisture, hotter and drier climates lengthen the wildfire season and lead to larger, more severe fires.20,21 Increased wildfire frequency and severity can result in the loss of soil organic carbon through combustion98 and postfire erosion.24 In boreal systems, increased fire frequency may lead to changes in forest type,99 while streamflow changes and permafrost thaw may trigger transition from peatland to forest.100,101 Interactions between fire, climate change, and human development are multifaceted and include not only warming-induced increases in wildfire but also management actions to reduce wildfire fuel, the effects of fire on human populations, postfire recovery, and fire-induced changes in forest type (KM 8.1). Drought, wildfire, and unsustainable land-use practices cause land to lose productivity, which may trigger desertification in arid and semiarid regions.
Changes in land cover influence local and regional climate through both biogeochemical and biophysical pathways. The biogeochemical effects of vegetation loss, including both immediate CO2 emissions and missed capacity for carbon sequestration (KM 6.1), have a warming impact at the planetary scale.102 Vegetation loss causes immediate changes to local and regional climate through biophysical effects (e.g., Jiang et al. 2021; Wang et al. 2016103,104), including exposed ground or snow (cooling the surface by reflecting more sunlight), reduced evapotranspiration (warming the surface and reducing moisture supply for rainfall), and a smoother surface (warming the surface by reducing heat loss to the atmosphere). The net impact of land-cover change on local climate depends on season, background climate, and vegetation type. Across the United States, forest disturbance or forest loss during the 2000s and 2010s caused a net local warming at both evergreen and deciduous sites in arid/semiarid, tropical, temperate, and boreal zones.105,106 This occurred because warming from the loss of transpiration more than compensated for the cooling effects of the more reflective land surface following forest loss; exceptions were found during boreal winter at high latitudes where strong cooling resulted from high albedo of exposed snow.105,107 Similarly, climate over forests is cooler than the surrounding croplands and urban areas, and the increase of forest cover following agricultural abandonment during 1920–1990 is connected to the observed cooling trend in the Southeast US.108
Indirect interactions also have impacts on US ecosystem resilience.1,109 Land-use decisions that consider the interactions of climate change and management can maintain and promote ecosystem resilience.83,110 For example, the thinning of some western forests that are experiencing drought increases the resilience of the forests to future trends of warming and drying.111
Changes in climate and land use offer opportunities for mitigation and adaptation, such as post-disturbance restoration of lands using climate-adapted species, which could increase biodiversity and resilience to climate change.112 Increasing land-based carbon storage may be achieved by shifts in land management (KM 6.3), for example by afforestation (Ch. 7), altered grazing practices (Ch. 11),53 modified crop management (Ch. 11), conserved agricultural lands,113 active restoration of disturbed lands,114 and the use of prescribed fire to avoid wildfire.115
Among all classes of land-cover change in the contiguous United States between 1985 and 2016, the largest net change in any class was an estimated gain of 50,660 square miles (131,209 km2) of developed lands, at an average rate of 1,634 square miles (4,233 km2) per year, primarily at the expense of forest and agricultural land,116 a trend that continues to the present (Figure 6.4). Urban heat island effects exacerbate the impacts of warming on heat hazards, which disproportionately harm low-income communities (KM 12.2; Figure 12.6; App. 4). Warming-induced increases in precipitation extremes lead to higher flash flood risks, with especially devastating effects in urban regions where impervious surfaces cannot absorb rainwater. Although widespread increases in intense rain are evident,117 river flooding trends are not consistently apparent across the US at present (KM 4.2);118 however, in urbanized basins, as urban development expands, the size of flood peaks increases.117,119,120 A resilient urban infrastructure, therefore, must be able to accommodate increased runoff from extreme storms (KM 12.2). Urbanization, through both urban land cover and increases in human-caused fine particulate matter, can alter atmospheric convection and precipitation, leading to stronger storms and more intense precipitation.121,122,123,124 Urban heat islands reduce low clouds, which can increase plant water stress and possibly play a role in increasing wildfire risk, particularly in the wildland–urban interface.125,126
The adverse effects of urbanization on climate and ecosystems can be partly alleviated through sustainable practices designed to improve urban resilience. Urban greenspace (e.g., urban forest, farming, gardening) can mitigate the urban heat island effects and flooding risks127,128,129 with varying degrees of effectiveness. While urban vegetation sequesters carbon during the growing season, the annual net carbon flux is uncertain.130,131,132 Additionally, urban farming brings food security benefits, with yields comparable to conventional agricultural yields.133
Increasing energy demand, combined with new extraction technologies, has resulted in an average of 50,000 new oil and gas wells established per year throughout central North America since 2000.134 Infrastructure for horizontal drilling and high-volume hydraulic fracturing has transformed millions of acres into industrialized landscapes, with reductions in ecosystem resilience, biodiversity, and the land carbon sink (e.g., Allred et al. 2015134). Reclamation of wells could become less successful with climate change.135 The efficacy and resilience of renewable energy systems are expected to be affected by climate change in ways that will vary with generation type and location 136 and may strain the energy system (KMs 5.1, 5.2, 5.3).
After declining for multiple decades, cropland area in the United States increased at a rate of approximately 1,500 square miles (approximately 4,000 km2) per year during 2008–2016 (Figure 6.4),137 attributable to increased domestic demand for corn ethanol and global demand for agricultural commodities as well as changes to conservation and crop insurance programs, interest rates, and possibly climate change–driven crop migration.138,139 New croplands tend to occupy areas with marginal biophysical characteristics (e.g., erosive soils, nutrient deficiency, climatic stress) but displace grasslands and conservation easements that are higher-quality wildlife habitat than the remaining natural lands.137 Expansion of agricultural area in the north-central United States has led to fragmentation of the remaining grassland, which limits the dispersal and population of native species (e.g., Wimberly et al. 2018140) and is expected to reduce ecosystem resilience. Conversion of grassland to cropland also contributes to carbon emissions from loss of soil organic carbon (KM 11.1).141 The recovery of plant biodiversity, productivity, and soil carbon following agricultural abandonment is slow,142 but the potential recovery of carbon in lands released from agricultural use is substantial, as has been shown by the large soil carbon gains made in land under the Conservation Reserve Program (KM 11.1).113 Soil carbon increases, as well as increases in other ecosystem services, can be accelerated through activities such as deliberate revegetation with woody and herbaceous perennials.143
Agricultural extensification influences precipitation, with the direction of change depending on the region and the type of natural land cover prior to its conversion to cropland. For example, replacing grassland with cropland over the Great Plains can cause summer precipitation to increase.144 Studies suggest that, in addition to increased area, intensification and irrigation are major causes of the observed increases in precipitation and decreases in temperature in the central US and Midwest145,146,147,148—changes that provide potentially more favorable conditions for crops and surrounding ecosystems. Land conversion to cropland without intensification was not associated with the observed cooling.146
People value the ability to choose among multiple land-use options, although the ability to make these choices is not always experienced equitably across society (KM 20.3). There are increasing and competing demands for future land-use changes to support agriculture, housing, and infrastructure; to contribute to climate change mitigation and adaptation; and to conserve and possibly restore natural lands for biodiversity, resilience, and spiritual or recreational use. Scenario analysis is used to explore different climate mitigation “storylines,” known as Shared Socioeconomic Pathways (SSPs; Table 3 in Guide to the Report), for how global land use, energy systems, and greenhouse gas emissions might evolve together under a set of standardized background driving forces such as changes in population, technology, and governance.149,150 Land-use representation within the range of SSPs includes differences in land-use regulation, land productivity, trade, land-based mitigation and adaptation (Figure 6.8), and food/diet choices, along with a corresponding range of land-use trends that result from these drivers (Figure 6.9).
Future land uses in the United States have been explored under several SSPs and at multiple spatial scales.151 Future land use within the SSPs (Figure 6.9) is projected to involve substantial departures from historic trends (Figure 6.4), with determinants of change and resulting land-use patterns varying spatially and with time, based on multiple drivers including land management, demographic change, and ecological shifts (e.g., Richter and Bixler 2022 152). Many scenarios assume continued agricultural productivity increases, allowing the total area of cropland for food production to remain stable or decline despite the increasing global population.150 Future land-use changes that limit global warming include reductions in grazing land associated with lower-animal-calorie diets and climate mitigation via reforestation or forest expansion. In addition, to offset fossil fuel use in other sectors, an often-dramatic expansion of bioenergy crops (producing nonedible plant material) is included in many scenarios. Large increases in urban area and reductions in forest area often accompany scenarios that involve greater levels of climate change.153 Although these scenarios are useful for exploring different possible land-use futures at the aggregate scale, they do not quantify the likelihood of different land-use changes.
Flexibility in future land-use decision-making may be limited by agricultural land needs. Climate change is estimated to be slowing the rate of crop yield increases globally;154,155 future land use will depend on the ability of the agricultural sector to adapt. Modeling results indicate that climate change–driven regional crop disruptions may emerge within 2–3 decades,156 although such disruptions would be minimized with the adoption of adaptation and intensification measures such as supplemental irrigation and updated crop varieties.157,158 There is also evidence of agricultural system adaptation through migration of crop cultivation ranges into more favorable climates in the United States and globally.159
Individual farmers and landowners experience these changes in the context of increased variability in yields and income. As much as one-fifth of recent US crop insurance losses can be attributed to climate change.160 Over time, adverse climate trends might affect the financial viability of current cropping practices and create pressure for individual producers to adopt adaptation practices (e.g., earlier planting dates, new crop varieties, modified tillage practices)161 or switch crops. Such impacts will disproportionately affect small rural landholders (KM 11.3). Some regions are expected to see opportunities for new cropping systems159,162 or for increasing the frequency of cropping on a given field.163
Future agricultural land requirements and associated climate feedbacks are sensitive to dietary choices and food waste.164 American diets are high in meat consumption, a land-intensive food source, and universal adoption of USDA dietary guidelines would lead to a net reduction in the total biophysical land requirement for US agriculture.165 Shifting toward diets even lower in animal products—potentially via novel plant-based meat substitutes166—could spare additional land and enable restoration of natural ecosystems.167,168 US agricultural land futures could also be influenced by a continuation of the reduced household food waste observed during the COVID-19 period.169,170
Mitigation scenarios that limit global warming to 1.5° or 2°C (2.7° or 3.6°F) above preindustrial levels imply large expansions of renewable energy production, electricity transmission, and land-based carbon mitigation (Ch. 32).171 In scenarios of net-zero emissions by 2050, wind turbines may be visible across more than 130 million acres, an area greater than Colorado and Wyoming combined (Figure 6.10).172 However, individual wind turbines have a small physical footprint, and can be sited in areas of intensive agriculture (Figure 6.11).173 While solar farms are more land-intensive than wind- and fossil-derived electricity sources,174 it may be possible to integrate them into agricultural landscapes in ways that preserve or even enhance agricultural production.175 Decarbonizing energy systems will require a multifold expansion in global production of key metals and minerals,176 although proposals to build new mines or expand existing mines in the United States have often faced intense local opposition.177
The purposeful use of vegetation to capture or store additional carbon is one of the largest but most uncertain elements in future land-use projections. Many scenarios rely on land-based mitigation measures,178 including land-intensive reforestation or carbon-negative bioenergy production to achieve carbon dioxide removal (CDR) from the atmosphere,172,179,180 often implying unprecedented rates of land-use change.181 Bioenergy is the most land-intensive form of renewable energy,174 although it is valued in integrated assessment models for providing fuels for long-haul aviation and freight transport in addition to CDR (KM 32.3). Future bioenergy expansion may rely on dedicated cellulosic biomass crops cultivated on low-value land to minimize conflicts with existing agricultural production,182,183 with positive or negative effects on ecosystem carbon storage depending on previous land use.184
Existing experience with land-based mitigation measures is limited, and the efficacy of forest carbon offsets, agricultural soil carbon enhancement, and first-generation biofuel programs remains controversial.185,186,187,188 Most of the limited CDR achieved to date has come from forest restoration and management, and current CDR deployment plans fall far short of the scale envisioned in many decarbonization scenarios.189 In the absence of such land-based mitigation measures, limiting global warming to below 1.5°C (2.7°F) will require even more aggressive emissions reductions190 or breakthroughs in competing technologies such as direct air capture of CO2.191
These mitigation trends imply new opportunities for landowners to generate additional revenues from leasing land for renewable energy generation or transmission, from government-run conservation payment programs, or from private carbon markets. However, these new opportunities also carry risks of conflict around conservation and the best use of public lands.
Future land-use choices also include adaptations to climate change such as locating infrastructure away from potential hazards, strengthening natural ecosystems as buffers to climate extremes (e.g., coastal forests and wetlands), and planting trees in urban areas to reduce heat stress.192 Many of these activities have mitigation co-benefits (e.g., urban trees also store carbon).193 Efforts to reduce land use–driven habitat fragmentation are also expected to decrease the risks of disease transmission from animals or insects to humans, as well as pandemics.194,195,196 All components of the food supply system are expected to be impacted by future land-use choices and climate change,194 which will be felt unequally across society (KM 11.2). Land-use planning in the United States will be determined by many decision-makers, including land managers at federal, state, and local levels, as well as private and Tribal landowners, and achieving consensus over future land-use decisions is expected to be challenging.197
The chapter lead (CL) and coordinating lead author (CLA) developed a list of relevant topics and the expertise needed to represent those topics in the assessment process. The CL and CLA reviewed a list of nominated authors, which included information about affiliation and expertise. The CL and CLA identified potential chapter authors from that list based on their knowledge of the field, their expertise in the topical areas, and their contribution to the diversity of the author team in terms of affiliations, gender, and race. Invitations were sent and updated as necessary to adequately cover the needed expertise.
All meetings of the author team were virtual, except for the all-author meeting held in Washington, DC, in April 2023. Consensus was built during weekly meetings of the full author team, with candidate content developed by author sub-teams through additional weekly meetings. All authors participated in developing and conducting a public stakeholder engagement workshop, and all authors participated in reviewing and responding to public comments.
For development of candidate text for each Key Message, the authors discussed the key topics that should be addressed based on their assessment of the literature, expert knowledge, and input from agency and stakeholder meetings. The authors then assigned topics according to expertise and performed a literature review to evaluate and synthesize information regarding land use and land-cover change, climate change, and related ecosystem controls. Based on this review, they developed Key Messages, central points, and examples to communicate the issues, challenges, and opportunities related to land system goods and services, land system resilience, and future land-use options.
Climate change has increased regional intensity and frequency of extreme rain, droughts, temperature highs, fires, and urban floods , posing increased risks for roads and other infrastructure, agricultural production, forests, biodiversity, carbon sinks, and human health . Climate-driven increases in wildfire extent and intensity are threatening the ability of some western forests to provide valued goods and services . Climate change has disrupted the ways that people interact with the landscape for spiritual practices, recreation, and subsistence .
Read about Confidence and Likelihood
Land-cover and land-use datasets for the US are detailed and reliable when considering a relatively small number of land-cover types and land-cover or land-use transitions, although the best available data for different regions (contiguous US, Alaska, Hawaiʻi, and Puerto Rico) cover slightly different time periods and use different though related methods.
There is consensus that more extreme rain will cause more landslides in a warmer climate, but the spatial distribution of anticipated future effects has not been resolved with much certainty; Gariano and Guzzetti (2016)10 provided a synthesis of many studies that, in total, support these interpretations. Some individual mass-movement events have been attributed directly to climate change, but many landslides are caused more directly by factors without a clear link to a warming climate, such as slope oversteepening (by human construction) or local soil, bedrock, and hydrologic conditions. A broad literature base supports these inferences. The link between climate and slope-failure hazards, including the characteristics of rainfall, terrain, and burn severity that contribute to postfire debris flows (e.g., Kean et al. 201922), is a rapidly growing research area.
The literature examining agricultural land practice and connections to climate change is broad and deep, covering many cropping and forestry practices in many regions across the US. There is a tendency for studies to focus more on small regions than on broad spatial patterns.
There is a long history of research into the connections between forest land cover and biodiversity, and this assessment drew on an extensive body of literature. These systems are complex, and the literature examines these connections from many perspectives.
While the topic of natural and managed carbon sinks on land is addressed by a large body of research, predictive understanding of interactions of the land carbon sink with land-use and land-cover change under a changing climate is still evolving (e.g., Zhu et al. 201861).
Land-use and land-cover datasets with good temporal coverage and detailed spatial information are still lacking or highly uncertain for high-latitude regions such as Alaska. Additional observations and synthesis of ground-based and remotely sensed data would be required to fill these gaps.
Geographic variation in the two-way interactions between climate change and agricultural practice points to gaps in understanding of the detailed mechanisms connecting agricultural practices to long-term climate variation.
Relationships between agricultural practice, forestry practice, and climate change in mixed-management agroforestry systems have received less attention than traditional cropping or forestry practices. To the extent that strong mitigation measures place higher demand on mixed-use systems for both production and carbon sequestration, additional effort would be required to fill these research gaps.
Comprehensive assessment of the many component fluxes and processes contributing to net greenhouse gas fluxes due to land-use and land-cover change is still an important gap at scales larger than a few tens of square miles. Regional and continental-scale studies continue to rely on sparse observations and relatively simple assumptions about how different disturbance types, frequencies, and intensities interact with ecological communities of vegetation and soil biota to drive long-term net fluxes between land and atmosphere.
Based on strong and abundant empirical evidence, there is high confidence that climate change is increasing the regional intensity and frequency of extreme events, including rain, droughts, temperature highs, and fire. There is likewise a strong theoretical foundation for the attribution of these effects to human-caused climate change at present and further evidence that these effects will increase in the future as greenhouse gas concentrations rise. The empirical and theoretical basis for attributing changes in flood frequency and intensity is also robust, but not as strong as for extreme precipitation, droughts, and fire.21,77 Based on abundant documentation, there is high confidence that these changes in weather and climate extremes cause risks to infrastructure, agriculture, ecosystems, and human health.
Broad empirical and theoretical understanding provides high confidence that wildfire is a major risk to the permanence of land carbon sinks, especially in woody ecosystems that have the potential to transition to savanna or grassland under increased fire frequency and/or severity. Other aspects of the net storage of carbon on land due to disturbances such as rotational forest harvest, windthrow, insect damage, and shifting agriculture are commonly identified as significant sources of uncertainty in estimating global or regional-scale carbon budgets.
Based on abundant documentation of climate change impacts on human–ecosystem interactions, there is high confidence that these impacts have negative consequences for subsistence, recreation, and spiritual practice. Some geographies and communities are more impacted than others, and fine-grained or predictive understanding of which communities and practices are most at risk is still being developed.
Changes in climate and land use affect the resilience of land ecosystems and thus the fate of the services they provide ; for example, increasing drought reduces the ability of forests to store carbon. Climate and land-use change interact, and these interactions present challenges as well as opportunities for maintaining ecosystem resilience .
Read about Confidence and Likelihood
The adverse impact of climate change (e.g., increased mean temperature, extreme heat, drought) on the resilience of land systems is supported by theory and observational studies involving a wide array of ecosystems, with overwhelming evidence in the United States coming from ecosystems that are increasingly influenced by drought, wildfire, and pests (e.g., Williams et al. 201921). There is also strong evidence for how the loss of natural lands leads to degradation of ecosystem services that are slow to recover (e.g., Isbell et al. 2019142). However, the extent to which different ecosystems may recover or management choices are able to maintain or rebuild ecosystem resilience is not well known.
Globally, there is a large body of literature on how land-use and land-cover changes might influence local and regional climate, and findings are often region- and scale-dependent. This assessment focuses on studies over subregions of the United States, some based on observational data analysis and others based on numerical model experiments. Of the observation-based studies, some took a space-for-time approach by comparing climate trends over different land types (e.g., irrigated versus rainfed cropland, forest versus cropland; e.g., Mueller et al. 2016146) while others were based on observations before and after sudden land-cover changes (e.g., Li et al. 2022106). In numerical modeling studies, land-use or land-cover changes were imposed over a corresponding subregion (e.g., intensification or irrigation over cropland in the central US or Midwest, converting cropland to forest in the Southeast) with experiments designed to distinguish the impact of land-use change from the impact of greenhouse gas warming. These studies compared model results with observed climate trends to enable the attribution of observed climate phenomena to land-use practice or land-cover changes (e.g., Alter et al. 2018145). Findings from these studies are mostly consistent.
Warming-induced intensification of rainfall increases the nitrate leaching from cropping systems to surface water and groundwater, which exacerbates the environmental effects of increased fertilizer application. Different land-use practices (e.g., no-tillage management versus conventional tillage) may influence nitrate leaching, but the impact remains uncertain based on recent literature, which limits the extent of this chapter’s assessment on this aspect.
A rich literature base supports the idea that while interactions between climate change, land use, land-cover change, and disturbance increase the risks of adverse impacts, they also provide multiple opportunities to reduce or lessen those impacts and ensure resilience.
The impact of urbanization on precipitation and other storms has been a topic of increasing research interest. Studies based on numerical modeling found a clear signal related to the enhancement of storm severity and precipitation (e.g., Debbage and Shepherd 2018119). However, observational data show a large degree of uncertainty and regional dependence. This is an important research gap.
Although geographically widespread increases in intense rain are evident, flooding trends are not consistently apparent at present.118 Whether intense rain leads to flooding depends on soil type and land use, urban water-conveyance capacity, and how well the urban storm drainage system is maintained.
There are important uncertainties related to interactions between invasive species, disease, and natural disturbance. There is some evidence that changes in temperature and precipitation, as well as altered fire regimes, may negatively impact the competitive ability of native species, facilitating invasion by pests and pathogens (e.g., Ravi et al. 202241). However, the outcomes are variable and seem to depend on multiple factors.
Research gaps and uncertainties also exist for the interactions of climate change with land-based renewable energy. Current research provides inconclusive results across the United States for all technologies.136
Based on a large literature base (e.g., Holden et al. 2018; Stephens et al. 201887,93), there is high confidence that climate change and climate change–related amplification of disturbance effects have a negative impact on ecosystem resilience.
Studies based on different methodologies (including observational data analyses and numerical model experiments) are consistent in suggesting that agricultural intensification and/or irrigation cause cooling and the increase of precipitation and atmospheric humidity in the central US during summer; similar climate effects were found in fall and winter resulting from the increase of forest cover in the southeastern US due to agricultural abandonment. Increased flooding was observed in urbanized basins (e.g., Hodgkins et al. 2019120); elsewhere, there is no clear signal of increased flooding risks despite the strong increase in extreme precipitation (frequency and intensity). Based on this understanding, there is high confidence that climate and land-use change interact and that these interactions present challenges as well as opportunities for maintaining ecosystem resilience.
The future of land use in the United States will depend on how energy and agricultural technology evolves, how the climate changes, and the degree to which we prioritize climate mitigation and adaptation in land-use decisions . US cropland area had been declining but has rebounded somewhat over the last 1–2 decades . Future cropland needs will depend on uncertain factors such as agricultural technology improvements, dietary shifts, and climate change impacts . Decarbonization will require a continued expansion of solar and wind energy generation and transmission infrastructure and may involve large land-use changes toward land-based mitigation measures, including reforestation, other natural climate solutions, and bioenergy crops .
Read about Confidence and Likelihood
The evidence base describing Shared Socioeconomic Pathway (SSP) scenarios is large and well developed, having already been used in multiple international studies by the Intergovernmental Panel on Climate Change (e.g., IPCC 2022180) and the Coupled Model Intercomparison Project simulations. The “storylines” from the SSPs are developed by integrated assessment models (IAMs) into modeled projections of societal changes across multiple sectors. These scenarios provide alternative realizations of future societal pathways that are consistent with specified climate targets.149,150 As such, they are useful for examining the range of possible challenges and changes facing our society over the rest of this century, although they do not provide predictions or probabilities of future trends.198
The Land-Use Harmonization 2 (LUH2) dataset provides a spatially explicit downscaling of the subset of SSP results used for the Scenario Model Intercomparison Project,199 harmonizes them with historical land-use reconstructions, and provides a consistent data input for Earth system model simulations.151 The LUH2 data provide global annual gridded (0.25° resolution) data of the fractional area occupied by 12 different land-use states, all transitions between those states, and land management data. The Land Change Monitoring, Assessment, and Projection (LCMAP) product described in the Introduction is a high-resolution annual land-cover dataset. That product complements the National Land Cover Database (NLCD),200 which has greater thematic detail but is updated less frequently.
US agricultural land use in particular is tracked by a variety of surveys (e.g., the Census of Agriculture [CoA]) and longitudinal methods (e.g., the National Resources Inventory [NRI]), producing data that can be used to calibrate and validate the previously described remote sensing–based datasets.8,137,201 Agricultural production is tracked through government statistics (e.g., the USDA National Agricultural Statistics Service), and crop yields are evaluated at finer spatial scales through crop insurance programs and combine yield monitors. The annual Inventory of US Greenhouse Gas Emissions and Sinks55 estimates emissions from US land-use change, using agricultural area data from NRI and other sources.
Understanding of mitigation-driven land-use changes draws on the large IAM scenario evidence base described previously. Additionally, the Princeton Net-Zero America Project172 is among the first to project where renewable electricity generation infrastructure might be sited at relatively fine spatial resolution.
Although human land-use activities have historically resulted in a net source of carbon emissions to the atmosphere, there is considerable uncertainty in these, and future, estimates.202
The SSP scenarios and harmonized land-use datasets are generated with a global focus. Although they can be analyzed and used for specific regional and national impacts, they are not likely to have US-specific levels of detail. In addition, the national-to-regional focus of these scenarios prevents the consideration of many societal equity and justice issues. Inequality and governance are included as drivers of land-use change in the SSPs, where they are used primarily to address inequality between countries and regions.203 The SSP datasets used by LUH2 were each produced by a single IAM; it is possible that alternative IAMs would represent land-use differently within each SSP, and those potential differences were not explored here. There are also very few studies that provide short-term predictive forecasts of national-level land-use changes over the next 1–2 decades.204 SSP scenario analyses do not include climate feedbacks to the future scenarios, but other studies using coupled human–climate models205 show that climate change is expected to modify the future land-use choices society is able to, or desires to, make.
Future agricultural land requirements will depend on various difficult-to-assess factors such as changing dietary preferences and climate change effects on crop yields. While IAM studies typically assume that historically observed rates of crop yield increase will continue into the future, more detailed modeling efforts such as the Agricultural Model Intercomparison Project (AgMIP)156 suggest that climate-driven reductions in corn yield in the western US may be clearly observable in as little as two decades under pessimistic emissions scenarios (SSP5-8.5), for example. The potential of in situ adaptation practices (e.g., adoption of different crop varieties or planting dates) to mitigate the severity of climate-driven disruptions is an active area of study, but the literature base on climate-driven shifts in crop cultivation range is still very limited.159 Studies show that dietary shifts away from animal products toward plant products have a large biophysical potential for reducing total agricultural land use and supporting natural ecosystem restoration and land-based mitigation.165,167,168 The SSP scenarios cover a range of dietary shift assumptions, including a shift toward low-meat diets in SSP1 and associated market and trade implications.150
The efficacy of existing land-based mitigation measures is often debated. For example, estimates of the mitigation value of US corn ethanol production diverge significantly187,188 depending on assumed counterfactual land use in the absence of ethanol production and the degree to which diversion of finite arable land might lead to unintended agricultural expansion elsewhere. While remote sensing provides an invaluable tool for tracking deforestation, it can struggle to differentiate more subtle land-use changes with similar land cover (for example, unmanaged native grasslands, rangeland, pastureland, hay land, cropland–pasture, idled cropland, and conservation reserves), making it difficult to distinguish between permanent agricultural expansion versus transient agricultural intensification.206 This ambiguity contributes to the debate around the viability and desirability of wide-scale land-based mitigation and carbon dioxide removal (CDR) measures in future decarbonization scenarios.
The land-use consequences of agricultural technology improvement (e.g., per-area crop yields, management intensity) and demand for land-based mitigation (including bioenergy and various CDR measures) are well explored in SSP scenario analyses.150,205 Other collaborations (e.g., AgMIP) have explored the interaction between crop productivity and future climate change beyond what has been possible in integrated assessment modeling. Together, these literatures point to the influences of technology, mitigation needs, and climate change on land-use futures, hence the high confidence rating.
Primary data on cultivated cropland area and/or total cropland area are available via remote-sensing datasets (NLCD and LCMAP), longitudinal studies (NRI), and surveys (CoA). The longer-duration NRI and LCMAP datasets support a net decline in US cropland area over the last three and a half decades for which data are available, consistent with longer-term land-use records showing a mid-20th-century peak in US cropland area.151 All four of these primary datasets are consistent with partial rebound of cropland area more recently, although with some disagreement around the starting year (as early as 2001 in NLCD or as late as 2012 in CoA) and magnitude of that rebound. Based on the agreement of these different primary data sources, there is high confidence of a long-term decline in US cropland area followed by a more recent rebound.
The LUH2 future scenarios all show stable or declining cropland use across the range of population growth and dietary shifts represented in the SSPs, although these scenario comparisons are not designed to represent the likelihood of different futures. Other literature suggests ongoing challenges in maintaining agricultural system resilience155 in the face of a changing climate. Thus, continuation of the trend of declining land use is given a medium confidence rating, since there is not only evidence for multiple enabling preconditions but also key risks that are not captured in most scenario assessments.
The scenario assessment literature is consistent in identifying expanded electricity generation from renewable sources (i.e., wind and solar) and more widespread electrification of energy end use as preconditions for decarbonization of the energy sector.171 This is consistent with recent trends of accelerating wind and energy deployment driven by the comparatively low cost of these energy sources, as well as policy support (e.g., through the Inflation Reduction Act), hence the very likely, high confidence rating. However, decarbonization scenarios have been widely criticized for over-reliance on land-intensive, technologically immature, or potentially unsustainable land-based mitigation and CDR measures,207,208,209 and a variety of alternative scenarios that avoid land-intensive CDR have been developed.190 Considering this, the statement about widespread land-use change for land-based mitigation is assigned a low confidence rating.
Virtually Certain | Very Likely | Likely | As Likely as Not | Unlikely | Very Unikely | Exceptionally Unlikely |
---|---|---|---|---|---|---|
99%–100% | 90%–100% | 66%–100% | 33%–66% | 0%–33% | 0%–10% | 0%–1% |
Very High | High | Medium | Low |
---|---|---|---|
|
|
|
|