Co-Written by John Crusius, Richard Gammon, and Steve Emerson
The scientific community is almost universally in agreement that climate change (and ocean acidification) are severe threats that demand a rapid response, with putting a price on fossil fuel CO2 emissions being a top priority. Far and away the single biggest contributor to climate change is CO2 emissions from fossil fuel combustion. Indeed, global CO2 emissions from fossil fuel emissions in recent years have been roughly ten times higher than emissions from the next largest global source, land use change, including deforestation (Le Quéré et al., 2015). Despite the small size of carbon fluxes from forests, enhancing carbon storage in forests is often discussed in WA state as a tool to fight climate change. There was one such claim in the Seattle Times OpEd from October 21 by Mathew Randazzo. We challenge these claims that forest carbon sequestration in WA state can significantly help solve climate change. Randazzo does not spell out in any detail what he means. As always, details matter in such discussions, as the science is complex. We focus here on some of the best available science on the climate and carbon storage impacts of forests, and provide references at the bottom of this article from some of the premier scientific journals in the world.
It is easy to understand why many wish carbon storage in WA state forests to be a viable tool to fight climate change, as forestry is an important industry in WA state. Such a solution, at first glance, seems like it could support the local forestry industry and create local jobs. However, mitigating climate change requires responses that make scientific sense. Devoting resources to forest carbon sequestration is largely a distraction from the real work needed to mitigate climate change, which is to reduce emissions of greenhouse gases, most importantly of CO2 from fossil fuel combustion. But before we explain the counterintuitive science, we wish to acknowledge at the start that there are many excellent reasons to support planting trees in WA state and to support the local forestry industry. However, mitigating the threat of climate change is not among those reasons, based on the available science.
In temperate parts of the world (mid to high latitudes), such as the Pacific northwest, the impacts of forests on climate are complex. Forest growth does take up CO2 from the atmosphere, which is the impact on climate many think of. However, forests have other, lesser known impacts on climate as well, including trapping moisture below the forest canopy and altering the way sunlight is reflected off the landscape (termed albedo). In temperate regions such as WA state, forests can actually warm the climate via these impacts on trapping moisture and reflectivity (albedo) more than they cool the climate by taking up CO2. This has been pointed out in a recent article on reforestation and forest management in Europe over the last 250 years that caused a net warming, not a net cooling (Naudts et al, 2016).
It is in the tropical and subtropical latitudes, far south of WA state, where science indicates carbon storage in forests could have the most beneficial effect on the world’s climate and could possibly help to buy time until society reduces fossil fuel emissions substantially (Houghton et al, 2015). Even in the tropics, relying on forest carbon storage is risky. Carbon stores could be re-released back into the atmosphere at any point in response to fire or disease, each of which can be made worse by climate change. Indeed, one recent study of forests in the Amazon region concluded that forests there went from taking up CO2 to releasing it during one dry year (Gatti et al, 2014). Furthermore, there have been suggestions that tropical forest may become a source of CO2, even in the tropics, in response to greater extremes of rainfall (Gatti et al, 2014). In order for carbon storage even in tropical forests to be beneficial, it must remain stored essentially permanently (for many hundreds to thousands of years). No one can guarantee that future climate change, disease, and/or land use change won’t cause release of this forest carbon back into the atmosphere, which would bring us back to the starting point, before any forest carbon storage efforts were even attempted.
It is urgent that society act quickly to minimize the risks posed by both climate change and ocean acidification. However, any solution must stand up to the rigorous test of the best available science. We quote from some journals cited below. “Considering carbon storage on land as a means to ‘offset’ CO2 emissions from burning fossil fuels (an idea with wide currency) is scientifically flawed” (Mackey et al, 2013). “Today’s forest management is more of a gamble than a scientific debate” (Bellassen and Luyssaert, 2014). “Above-ground carbon in forests represents a vulnerable pool of carbon, subject to droughts, fires, insects and other disturbances. Thus, the management of forests to accumulate carbon must not delay or dilute the phasing-out fossil fuel use. On the contrary, the deliberate accumulation of carbon on land may be of little long-term benefit” (Houghton et al, 2015). “Relying on biospheric sequestration is not without risk, because such sequestration is reversible from either climate changes, direct human actions, or a combination of both” (Pan et al, 2011). The best science tells us that relying on storage of carbon in WA state forests is risky at best, and quite possibly counterproductive. It is also in many ways a distraction from the essential efforts to reduce emissions of CO2 from fossil fuels.
John Crusius, Ph.D.
Richard Gammon, Emeritus Professor, UW Department of Chemistry, UW School of Oceanography
Steven Emerson, Professor, UW School of Oceanography
Bellassen, V., and S. Luyssaert (2014), Managing forests in uncertain times, Nature, 506(7487), 153-155.
Brienen, R. J. W., et al. (2015), Long-term decline of the Amazon carbon sink, Nature, 519(7543), 344-+, doi:10.1038/nature14283.
Gatti, L. V., et al. (2014), Drought sensitivity of Amazonian carbon balance revealed by atmospheric measurements, Nature, 506(7486), 76-+, doi:10.1038/nature12957.
Houghton, R. A., B. Byers, and A. A. Nassikas (2015), COMMENTARY: A role for tropical forests in stabilizing atmospheric CO2, NATURE CLIMATE CHANGE, 5, 1022-1023.
Le Quéré, C., et al. (2015), Global Carbon Budget 2014, Earth Syst. Sci. Data, 7, 47-85,
771 doi: 10.5194/essd-7-47-2015.
Mackey, B., I. C. Prentice, W. Steffen, J. I. House, D. Lindenmayer, H. Keith, and S. Berry (2013), Untangling the confusion around land carbon science and climate change mitigation policy, Nature Climate Change, 3(6), 552-557, doi:10.1038/nclimate1804.
Naudts, K., Y. Chen, M. J. McGrath, J. Ryder, A. Valade, J. Otto, and S. Luyssaert (2016), Europe’s forest management did not mitigate climate warming, Science, 351(6273), 597-600, doi:10.1126/science.aad7270.
Pan, Y. D., et al. (2011), A Large and Persistent Carbon Sink in the World’s Forests, Science, 333(6045), 988-993, doi:10.1126/science.1201609.
Originally published in RealClimete.org