labs_title

Caldeira Lab Research:Land Plants, Carbon, and Climate

Protecting climate with forests

Robert B. Jackson, James T. Randerson, Josep G. Canadell, Ray G. Anderson, Roni Avissar, Dennis D. Baldocchi, Gordon B. Bonan, Ken Caldeira, Noah S. Diffenbaugh, Christopher B. Field, Bruce A. Hungate, Esteban G. Jobbagy, Lara M. Kueppers, Marcelo D. Nosetto & Diane E. Pataki

Climate mitigation policies often only take into account their effect on atmospheric CO2. However, implementing projects such as widespread afforestation would have many biophysical effects as well that could change temperature even more than carbon dioxide. Ignoring these effects could lead to the implementation of projects that are in fact counter productive.


Jackson, R. B.; Randerson, J. T.; Canadell, J. G.; Anderson, R. G.; Avissar, R.; Baldocchi, D. D.; Bonan, G. B.; Caldeira, K.; Diffenbaugh, N. S.; Field, C. B.; Hungate, B. A.; Jobbagy, E. G.; Kueppers, L. M.; Nosetto, M. D.; Pataki, D. E., 2008. Protecting climate with forests, Environmental Research Letters 3 (4):44006.

Biophysical factors of various kinds of land: Croplands (A) have higher albedo (reflectivity) than forests (B), so they reflect more sunlight back into the atmosphere, resulting in less surface heat. However, more evaporation takes place in forests, which transmits heat back into the atmosphere. Several conflicting factors lead to warming and cooling effects from different kinds of lands, making it no simple task to determine what will be effective at mitigating climate change.

Surface albedo for different vegetation types: Albedo measured in the northwest (a), northeast (b), southwest (c), and southeast (d) for croplands, grasslands, and forest. Croplands and grassland show substantially higher albedo than forests in each measurement.

Abstract

Policies for climate mitigation on land rarely acknowledge biophysical factors, such as reflectivity, evaporation, and surface roughness. Yet such factors can alter temperatures much more than carbon sequestration does, and often in a conflicting way. We outline a framework for examining biophysical factors in mitigation policies and provide some best-practice recommendations based on that framework. Tropical projects—avoided deforestation, forest restoration, and afforestation—provide the greatest climate value, because carbon storage and biophysics align to cool the Earth. In contrast, the climate benefits of carbon storage are often counteracted in boreal and other snow-covered regions, where darker trees trap more heat than snow does. Managers can increase the climate benefit of some forest projects by using more reflective and deciduous species and through urban forestry projects that reduce energy use. Ignoring biophysical interactions could result in millions of dollars being invested in some mitigation projects that provide little climate benefit or, worse, are counter-productive.