To Tree or Not to Tree? How to Reduce Greenhouse Gases
I’m happy to report that, to my surprise, my recent newspaper columns on global warming have caused some consternation. I’m not surprised that the columns have upset some people who don’t believe in global warming, of course; I expected that.
But I was surprised that some people who take the threat of global warming very seriously were upset as well — because they thought that my proposed solutions were fanciful. In fact, one biophysicist wrote me an extensive email about a perceived flaw in my proposal, and one climate scientist drove from a nearby town to discuss my ideas over coffee.
I was honored that these gentlemen wanted to make sure my proposed global warming solutions are realistic and not misleading the public. However, their concerns were based on a misreading of my proposal, possibly because it was presented in abbreviated, newspaper column formats.
My proposal was that we take a three-step approach to solving global warming: (1) enact serious energy conservation measures, (2) reduce greenhouse gases that are already in the atmosphere by sequestering them in plant biomass (biosequetration) — mostly, initially, by planting millions of trees and, (3) speed up the transition to affordable, earth-friendly technologies (appropriate technology), especially in the energy sector.
Based on my discussion of biosequestration, both scientists thought I was claiming that we can solve global warming simply by planting trees. They both pointed out that trees grow too slowly to keep up with the pace of greenhouse gas emissions (especially CO2), and that all of the world’s trees combined sequester far too little CO2 to adequately “scrub” the atmosphere of the excess gas. We need to stop emitting CO2 (and other greenhouse gases), not clean up with trees after the fact.
I completely agree. But I want to be clear, as I explained to my scientist critics (much to their relief), that I never proposed that biosequestration by itself would adequately reduce greenhouse gases. To understand why, we have to look at some elementary numbers.
Humans are currently adding about 30 billions tons of CO2 to the atmosphere each year. Roughly 80 percent of that comes from burning fossil fuels; most of the rest comes from burning forests and agricultural waste. So to simply stop overloading the atmosphere, we’d have to reduce emissions by 30 billion tons a year.
But we also need to remove some of the CO2 that we’ve already added to the atmosphere to get us closer to pre-industrial levels. (Our current CO2 level of 392 parts per million [ppm] is over 30 percent higher than the pre-industrial level of 280 ppm.)
I’ve recently revised my thinking on this matter, concluding that rather than allowing CO2 to build up to 450 ppm, the maximum safe level suggested by many climate scientists, we need to revert to a level of 350 ppm or less, as environmentalist Bill McKibben and former NASA climatologist Jim Hansen state. (See McKibben’s web site and the book “Storms of My Grandchildren” by Jim Hansen.)
Why should we revert to 350 ppm?
Because we are already seeing damage from global warming. And because the amount of warming we can expect from current CO2 levels is already sufficient to melt enough of Greenland and Antarctica’s ice to cause dangerous sea-level rises that can flood the world’s coastal cities in the near future. Since CO2 doesn’t just “go away,” but persists in the atmosphere for at least several hundred years, we must remove some of the existing CO2 to avoid the catastrophic — and largely irreversible — melting of ice.
That’s where the “trees” (biosequestration) come in. Plants sequester tens of billion of tons of CO2 annually in their biomass, and, if we plant enough of them and manage our forests and farms correctly, they can gradually reduce greenhouse gases to pre-industrial levels and, with luck, stabilize the climate.
But there’s a catch. Plants release most of their CO2 back into the atmosphere when they decompose after dying, so to remove the gas we need to convert some of the plant biomass into a form that can be permanently sequestered. Fortunately, biomass is readily converted into “biochar” (charcoal) that is useful as a soil amendment and can be sequestered in soil for centuries.
Biochar potentially can sequester about 30 percent of plant biomass, roughly equivalent to five billion tons of atmospheric CO2 annually. What about reducing the other 25 (plus) billion tons of annual CO2 loading? Stay tuned for appropriate energy technology solutions.
This post is a modified version of an article that was originally written as syndicated newspaper column, published in various locations around the U.S. in March, 2012.
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Deforestation and Climate Change, Bosetti and Lubowski
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Related Links On Ecotecture:
Global Warming Solution? The Framework for a Plan (1st article in this series)
Global Warming Solution? Energy Conservation and Carbon Biostorage (2nd article in this series)
Global Warming Solutions? Artificial Trees versus Real Forests (3rd article in this series)
Comments are welcome and generally will be posted if they are on topic and inoffensive. However, Ecotecture does not post comments to the effect that global warming is a hoax. Read our position on global warming here.