Are Trees Good or Bad for Climate Change? Nature News Story

At 304 metres high, the Zotino Tall Tower Observatory measures gases and aerosols above taiga forest in central Siberia. A similar tall tower in the Amazon makes measurements above the tropical rainforest.Credit: Michael Hielscher/MPI


Forests (albeit not so much individual tree species) tend to pretty much do their own thing without human intervention. Sometimes humans cut forests down, and other times humans plant trees. In the Nature article here, case, people are researching whether it makes sense to do these activities specifically for climate change mitigation reasons.  There are separate issues around changing forests for adaptive reasons (e.g., increasing resilience through encouraging diverse species, more fires means greater need for fuel treatments, cut trees to increase water supplies and so on).  In all of these discussions, climate change factors have to take their place in the universe of other pros and cons of changing forest management.

There’s quite a bit about VOC’s in this article as well as albedo.  The VOC’s may remind you of Ronald Reagan and his famous quote about polluting trees (for those of you of a certain age). Here’s a link to a story about that from 2004. But now back to the Nature news story.

Researchers are now turning to sophisticated computer models and using larger and more-comprehensive data sets to nail down exactly what forests in different places do to the climate. In some cases, the results have been sobering. Last October, a team led by ecologist Sebastiaan Luyssaert at the Free University of Amsterdam modelled a variety of European forest-management scenarios8. The researchers concluded that none of the scenarios would yield a significant global climate impact, because the effects of surface darkening and cloud-cover changes from any added forests would roughly eliminate their carbon-storage benefits.

To estimate the climate impact of planting forests in different parts of the United States, ecologist Christopher Williams at Clark University in Worcester, Massachusetts, is combining global satellite data collected over more than a decade with carbon-sequestration figures based on data from the US Forest Service. He has found in preliminary work that adding trees to the US west coast and to regions east of the Mississippi River makes sense, climatically speaking. But albedo changes make forest planting in the Rockies and the southwestern United States a bad deal for the climate in most cases, because the conifers that thrive in those regions are dark and absorb more sunlight than do underlying soils or snow. He hopes to turn this research into a standardized methodology that forest managers can use to assess a project’s climate impact.

Getting planners to adopt such methods could prove challenging, however. Williams has found that some resist considering albedo effects, including representatives of companies hoping to sell carbon credits for forest projects. “Even other scientists sometimes have disbelief in the magnitude of the albedo effect, or even its existence,” he says.

“I have heard scientists say that if we found forest loss cooled the planet, we wouldn’t publish it.”

These controversies may be important to people doing carbon credit trading (which is rife with other issues and problems).  Maybe one of the reasons people in the Southwest and Rockies may still want to plant trees is that they provide valuable ecosystem services regardless of climate impacts. Maybe this is one of those cases in which people might not use scientific information, not because scientists disagree and are waiting for a degree of completeness or agreement, nor because of a mistrust of models with unknown measurements and assumptions, but because climate is one environmental concern, but not always the top one.



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