Back in 2009, I described various ways to try to deliberately engineer the Earth system to reduce the severity of climate change and noted:
The first way to do this is to encourage the growth of biomass. This is relatively easy, but has limited potential. Biomass is like a giant carbon cushion: it can be thick or thin, but it cannot keep growing forever. Increasing the amount of biomass on Earth could draw down the amount of CO2 in the atmosphere a bit, but only if we also manage to cut our greenhouse gas emissions to practically zero.
Now that Prime Minister Trudeau has pledged to plant 2 billion trees as a climate solution (using expected pipeline revenue, to try to justify Canada’s continuing fossil fuel expansion) it’s worth having a post specifically on the limited ability of tree-planting to combat the problem.
A recent Slate article notes:
The notion that any significant percent of the carbon humanity spews can be sucked up by planted trees is a pipe dream. But it got rocket boosters in July, when Zurich’s Crowther Lab published a paper, in Science, proclaiming that planting a trillion trees could store “25 percent of the current atmospheric carbon pool.” That assertion is ridiculous, because planting a trillion trees, one-third of all trees currently on earth, is impossible. Even a start would require the destruction of grasslands (prairies, rangelands, and savannas) that reflect rather than absorb solar heat and that, with current climate conditions, are better carbon sinks than natural forests, let alone plantations. Also, unlike trees, grasslands store most of their carbon underground, so it’s not released when they burn.
The Crowther paper horrified climate scientists and ecologists, 46 of whom wrote a rebuttal, explaining that planting trees in the wrong places would exacerbate global warming, create fire hazards, and devastate wildlife. They rebuked the authors for “suggesting grasslands and savannas as potential sites for restoration using trees” and for overestimating by a factor of 5 “potential for new trees to capture carbon.”
Counter-intuitively, growing trees in order to burn them could actually be more of a climate solution, provided we develop the carbon capture and storage technology and infrastructure needed to bury the resulting CO2.
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