Afforestation in a warm and high-CO2 world

Foto: Julia Pongratz, MPI-M

In a new study, Sebastian Sonntag, Julia Pongratz, Christian Reick, and Hauke Schmidt, scientists at the Max Planck Institute for Meteorology (MPI-M), show that afforestation can contribute more to the mitigation of climate change than what has been estimated previously. Their findings have recently been published in Geophysical Research Letters.

Since land use changes strongly affect the exchange of carbon between atmosphere and land, increasing the terrestrial carbon sinks by extending the world's forest cover has been frequently suggested as a tool to reduce global warming. However, earlier assessments investigated afforestation mostly under present-day environmental conditions, neglecting future changes in climate and CO2. Further, side effects on energy and water fluxes are still incompletely understood. For example, increased forest cover can lead to a warming due to the darker land surface compared to non-forested areas, but can also lead to cooling because of a higher leaf area that can evaporate water.

In the recent publication the authors study the potential climate effects of strong reforestation under a high-CO2-emission scenario using the Max Planck Institute Earth System Model (MPI-ESM). They find that the simulated carbon sequestration potential is higher than previous estimates and is due to the combined effect of land use changes and enhanced carbon uptake of the terrestrial biosphere in a warm and high-CO2 climate. In their simulations, reforestation leads to a slight reduction of global warming by the end of the century compared to a reference scenario that includes deforestation. Since only small reductions in the annual mean warming are found in densely populated areas, reforestation has only minor consequences for the need to adapt to global warming in those regions. Yet, the results also suggest that the reduction of temperature extremes can reduce the need for adaptation in some regions.

The design of the study also allows for the first time to isolate the land use change effects from those of other anthropogenic forcings due to greenhouse gas or aerosol emissions in the IPCC/CMIP5 scenarios. This is achieved by prescribing in the MPI-ESM simulations CO2 emissions due to fossil fuel burning and cement production according to the high-emission scenario RCP8.5, but land use transitions according to the strong-reforestation scenario RCP4.5. In this mixed RCP scenario the CO2 concentration at the end of the 21st century is reduced by 85ppm (about 10% of the projected increase) compared to the standard RCP8.5 scenario. To investigate the dependence of these findings on specific model formulations, similar simulations are planned for the upcoming Coupled Model Intercomparison Project 6 (CMIP6).

Original publication:
Sonntag, S., J. Pongratz, C.H. Reick, and H. Schmidt (2016). Reforestation in a high-CO2 world - Higher mitigation potential than expected, lower adaptation potential than hoped for. Geophysical Research Letters, 43, 1-8, Opens external link in current windowdoi: 10.1002/2016GL068824

Contact:

Dr Sebastian Sonntag
Max Planck Institute for Meteorology
Phone: +49 40 41173 437
Email: Opens window for sending emailsebastian.sonntag@we dont want spammpimet.mpg.de

Dr Julia Pongratz
Max Planck Institute for Meteorology
Phone: +49 40 41173 255
Email: Opens window for sending emailjulia.pongratz@we dont want spammpimet.mpg.de