Attributing the carbon cycle impacts of CMIP5 historical and tuture land use and land cover change in the Community Earth System Model (CESM1)

Historical global land use and land cover change (LULCC) emissions of 160PgC represent a third of all human CO2 emissions from 1850 to 2010. Future land management decisions will have large impacts on the global carbon cycle, with scenarios ranging from continued deforestation and wood harvest to mitigation scenarios that reduce total emissions through afforestation and conversion to bioenergy. Here we present a systematic assessment of Community Earth System Model (CESM1) Coupled Model Intercomparison Project phase 5 (CMIP5) historic and projection simulations, with and without LULCC. For the historical period, CESM produced a Net LULCC flux of 123PgC to the atmosphere, removing -130PgC from ecosystems while increasing wood product pools by 7PgC. Historical LULCC fluxes were equally divided between conversion and wood harvest fluxes. For the Representative Concentration Pathway (RCP) 4.5 afforestation scenario CESM produced a Net LULCC flux of 53PgC to the atmosphere, removing -58PgC out of the ecosystem and increasing wood product pools of 5PgC. The afforestation offsets the Direct LULCC flux of 153PgC with a negative Indirect LULCC flux of -94PgC. For the RCP 8.5 high LULCC scenario, CESM produced a Net LULCC flux of 211PgC, removing -227PgC from ecosystems and increasing wood product pools of 15PgC. The LULCC of the future RCP scenarios was dominated by wood harvest fluxes, which is a process that was not included in many of the CMIP5 models. The analysis framework also allowed the attribution of Indirect and Prior LULCC fluxes that offset the Direct LULCC fluxes in many cases.