Potential climate forcing of land use and land cover change

Abstract

Abstract. Pressure on land resources is expected to increase as global population continues to climb and the world becomes more affluent, swelling the demand for food. Changing climate may exert additional pressures on natural lands as present-day productive regions may shift, or soil quality may degrade, and the recent rise in demand for biofuels increases competition with edible crops for arable land. Given these projected trends there is a need to understand the global climate impacts of land use and land cover change (LULCC). Here we quantify the climate impacts of global LULCC in terms of modifications to the balance between incoming and outgoing radiation at the top of the atmosphere (radiative forcing, RF) that are caused by changes in long-lived and short-lived greenhouse gas concentrations, aerosol effects, and land surface albedo. We attribute historical changes in terrestrial carbon storage, global fire emissions, secondary organic aerosol emissions, and surface albedo to LULCC using simulations with the Community Land Model version 3.5. These LULCC emissions are combined with estimates of agricultural emissions of important trace gases and mineral dust in two sets of Community Atmosphere Model simulations to calculate the RF of changes in atmospheric chemistry and aerosol concentrations attributed to LULCC. With all forcing agents considered together, we show that 40 % (±16 %) of the present-day anthropogenic RF can be attributed to LULCC. Changes in the emission of non-CO 2 greenhouse gases and aerosols from LULCC enhance the total LULCC RF by a factor of 2 to 3 with respect to the LULCC RF from CO 2 alone. This enhancement factor also applies to projected LULCC RF, which we compute for four future scenarios associated with the Representative Concentration Pathways. We attribute total RFs between 0.9 and 1.9 W m −2 to LULCC for the year 2100 (relative to a preindustrial state). To place an upper bound on the potential of LULCC to alter the global radiation budget, we include a fifth scenario in which all arable land is cultivated by 2100. This theoretical extreme case leads to a LULCC RF of 3.9 W m −2 (±0.9 W m −2 ), suggesting that not only energy policy but also land policy is necessary to minimize future increases in RF and associated climate changes.

The impact of historical land use change from 1850 to 2000 on secondary particulate matter and ozone

“…Therefore, the substantial difference between our estimate and that of Unger (2014) is associated with the uncertainty in characterizing BVOC basal emission rates from pasturelands, which expand significantly from 1850 to 2000. Ward et al (2014) estimate only a 1 % increase in all biogenic emissions due to historical LULCC, but they do not disaggregate BVOCs and we cannot compare simulated changes in terpenes directly. Figure 5 shows the estimated increases in nitrogen emissions associated with LUC.…”

“…Regular fire emissions associated with land use change, such as agricultural waste burning, make up less than 5 % of global annual smoke emissions (van der Werf et al, 2010). Ward et al (2014) explore the impacts of historical LULCC impacts on dust and smoke. In this study we focus on the impact of land use change on secondary aerosol and ozone formation.…”

“…This parameterization includes biome-specific emissions, as well as reemission of wet and dry deposited nitrogen and fertilizer and manure nitrogen, all modulated online by temperature, soil moisture, and rain. Finally, dry deposition is based on the resistance-in-series scheme of Wesely (1989), with aerosolspecific deposition described by Zhang et al (2001). The surface resistance for gases includes resistances to the ground, lower canopy, and vegetation, all of which are driven by fixed parameters for 11 land use types specified in the original Wesely (1989) parameterization.…”

“…As a result, anthropogenic land use change is absent from most estimates of radiative forcing from aerosols and tropospheric ozone. Ward et al (2014) investigate the impact of land use and land cover change (LULCC) on greenhouse gases (including tropospheric ozone) and aerosols. They estimate that historical changes in LULCC result in a radiative forcing of +0.12 W m −2 for ozone and −0.04 W m −2 for aerosols (−0.02 W m −2 direct, −0.02 W m −2 indirect) relative to 1850.…”

Continuous and consistent land use/cover change estimates using socio-ecological data

“…Land use/cover change (LULCC) is an important concern for global environmental sustainability because it can adversely affect surface albedo and heating (Davin and de NobletDucoudré, 2010), evapotranspiration and other components of the hydrologic cycle (Sterling et al, 2013), local to regional climate with the coupling or indirect recycling of surface moisture (Makarieva et al, 2013), global climate via carbon and other greenhouse gas emissions (Anderson-Teixeira and DeLucia, 2011;Ward et al, 2014), and ecosystem services worsened by these impacts (Turner et al, 2013). Land surface models, which can be coupled to a regional or global climate model, are used to simulate land-atmosphere interactions retrospectively or prospectively (Pitman, 2003) to identify intervention "hotspots" or develop realistic land management scenarios at the macroscale (Turner et al, 2007).…”