Cooperative Institute for Climate Science

Through practices such as forest clearance and cropland cultivation, humans have altered 42-68% of the Earth's surface and added over a hundred billion tons of carbon dioxide (CO2) to the atmosphere. Elena Shevliakova and colleagues of the Cooperative Institute for Climate Science (CICS) at Princeton University used a new land model LM3V to provide a global estimate of how much of the CO2 emitted from land has been offset by forest re-growth. They used four different scenarios, and found that even extensive human interference caused the net loss of only 1.1-1.3 billion tons of carbon per year in the 1990s - about half of previous estimates. One factor that may explain this is the 0.35-0.6 billion tons of carbon per year absorbed by plants growing back after disturbance, mostly in tropical forests.

Background: The new land model LM3V was developed in collaboration with the scientists from the Geophysical Fluid Dynamics Laboratory (GFDL) and is a component of the GFDL Earth System Models (ESMs). ESMs will be used in the next, 5th assessment of Intergovernmental Panel on Climate Change (IPCC) to explore interactions between the carbon cycle, climate change, and land cover changes. LM3V is specifically designed to address the consequences of human activities including cropland and pasture dynamics, shifting cultivation, logging, fire, and resulting patterns of secondary re-growth.

Significance: The smaller magnitude of the land-use source relative to previous estimates implies a smaller magnitude of the “missing sink,” that scientists have been seeking to help them balance the global carbon budget. LM3V provides GFDL ESMs with modeling capabilities to explore the consequences of land-use/land-management changes and its implications for climate in the past and under future scenarios.