Understanding the role of land management for carbon and climate mitigation under RCP 4.5 and RCP 8.5 using the Community Earth System Model

Abstract:

As part of the Coupled Model Intercomparison Project phase 5 (CMIP5), land cover change and wood harvest were prescribed as major climate forcings for historical and future Representative Concentration Pathway (RCP) projections. Lawrence et al. (2012) described how land cover change was prescribed in all of these simulations and how the climate system and carbon cycle responded to the land cover change in concert to other transient forcing in the Community Earth System Model (CESM). The attribution of carbon cycle and climate changes directly due to land cover change however, were not possible due to the design of the CMIP5 experiments. Through a series of new CESM simulations we have attributed the land cover change impacts for the historical time series as well as RCP 4.5 and RCP 8.5 with and without land cover change. These simulations show that the direct land cover change fluxes to the atmosphere found in the CMIP5 simulations did not account for the lost uptake of carbon that would have been possible in the absence of land cover change and wood harvest. Once these losses are taken into account, the historical losses of terrestrial carbon increased from 61.2 PgC to 129.6 PgC, the RCP 4.5 uptake of 62.8 PgC changed to a loss of 5.8 PgC, and the RCP 8.5 loss of 49.0 PgC increased to 168.8 PgC. In order to assess the potential of land management to mitigate carbon and climate consequences we extended the RCP 4.5 and RCP 8.5 experiments with large scale global afforestation compared to maximum agricultural expansion scenarios. In these experiments we found that afforestation was able to take up 220 PgC over the next 85 years, while large scale crop expansion could release the same amount of carbon from terrestrial ecosystems. Figure 1 shows the time series for global ecosystem carbon along with the spatial distribution of gains and losses under the maximum afforestation and agricultural expansion simulations. In comparison to fossil fuel emissions the land cover change carbon amounts were around 25% of RCP 4.5 and 12% of RCP 8.5. In this talk we present the differences in each of these experiments for both ecosystem carbon and climate.