Climate can drive changes in land cover and land use in several ways, including changes in the suitability of agriculture (Ch. 10: Ag & Rural),125,126 increases in fire frequency and extent (Ch. 6: Forests),18,101 the loss or migration of coastal wetlands,127 and the spatial relocation of natural vegetation. The extent of the climate influence is often difficult to determine, given that changes occur within interconnected physical and socioeconomic systems, and there is a lack of comprehensive observational evidence to support the development of predictive models, leaving a large degree of uncertainty related to these future changes (Ch. 17: Complex Systems). Models can be used to demonstrate how climate change may impact the production of a given agricultural commodity and/or suggest a change in land use (for example, econometric models, global gridded crop models, and integrated assessment models). However, the true impact may be mitigated by the influence of global economic markets, a shift to a different crop that is better suited to the new climate pattern, technological innovations, policy incentives, or capital improvement projects. This area of integrated, multidisciplinary scientific research is just emerging.
Important feedbacks with agriculture are anticipated under changing climate conditions. Recent trends show a shift from dryland farming to irrigated agriculture throughout much of the Great Plains region (Ch. 22: N. Great Plains; Ch. 23: S. Great Plains).117 Future projections suggest that cropland suitability may increase at higher latitudes128 and that croplands could shift to livestock grazing southward.126 For high-latitude regions, climate change could result in a large-scale transformation from naturally vegetated ecosystems to agronomy-dominated systems. Climate warming also could result in a shift from higher-productivity systems (such as irrigated agriculture) to lower-productivity systems (such as dryland farming).129 Due to the globally interconnected nature of agricultural systems, climate change has broad implications for food security (Ch. 16: International).130 Energy policies have also influenced the type and location of agricultural activities; for example, nearly two-thirds of recent land area converted for energy use was due to biofuel expansion34,131 mandated by the Energy Independence and Security Act of 2007.30,131 By 2040, the total new land area impacted by energy development could exceed an area the size of Texas—2,700 square miles per year,34 which is more than two times higher than the historical rate of urbanization.2
Natural disturbances such as wildfires can trigger changes in land cover that have the potential to result in a permanent land-cover conversion. Over the past several decades, drought,132 climate warming, and earlier spring snowmelt have led to an increase in fire activity across the United States (Ch. 6: Forests),18,133 although the burnt area increase may be partly due to changes in fire suppression policies.134 Under future warming scenarios (that is, A1B, as described here), the burnt area in southwestern California could double by 2050 and increase by 35% in the Sierra Nevada due to an increase in the length of the fire season and an increase in warmer and drier days.135 Human activity will continue to play an important role in wildfire frequency and intensity. Hot spots of fire activity were identified at the wildland–urban interface,136 and urbanization is expected to increase fire hazard exposure to people and property. Land management strategies, such as prescribed burning, fuel reduction and clearing, invasive species management, and forest thinning, have the potential to mitigate wildland fire and its associated consequences,137 but more research is needed to evaluate their efficacy across a range of spatial and temporal scales.
Current relationships between plant species and climate variables138 have been used to estimate potential changes in the geographic distribution of species and vegetation under future climate conditions.12,139,140,141,142,143 Studies have projected the conversion of forests to shrubland and grassland across some areas of the western United States due to increasing aridity, pest outbreaks, and fire, resulting in a substantial transfer of carbon from the biosphere to the atmosphere.144,145 For example, increases in mountainous forests and grasslands at the expense of alpine and subalpine communities have been projected.146 Across North America, projected changes include an expansion of tropical dry deciduous forests and desert shrub/scrub biomes, a poleward migration of deciduous and boreal forests, and an expansion of grasslands at the expense of high-latitude taiga and tundra communities.12,144,146,147,148,149 However, it is important to note that projecting the future distributions of vegetation and land cover is highly complex, driven not only by changes in climate but also land-use changes, shifts in disturbance regimes, interactions between species, and evolutionary changes.150