Lately I’ve been listening to some talks on climate change, such as this one by Prof. Kevin Anderson, and the news, not surprisingly, keeps getting worse. Anderson discusses many factors that have generally been ignored in official reports that claim to chart a course forward on the climate, including: a) a limit of 2C of warming is no longer really possible based upon the assumptions that they make, b) that 2C was probably the wrong target anyway, c) major reports make very unreasonable assumptions about how quickly emissions can turn around, d) we need to decrease carbon emissions by 70 percent by 2020 to stay below 2C (if we’re serious about that target), and e) 4C is more do-able as a target but also can’t support large-scale agriculture and thus civilization.
Anderson’s and other talks have led me to conclude that:
a) large-scale demand-side changes are really the only option to deal with climate change in the time we have,
b) peak oil will help with that, but the zeal to find new sources of oil/coal/gas will keep peak oil from really being a ‘solution’ to climate change (consider the crazy in-progress moves to drill for oil in the arctic), and
c) the demand-side decrease, however it is implemented, would cause in the near-term (the next decade) a major economic shock.
So my new summary for our predicament is (which hasn’t changed all that much, I suppose), in the vein of the CAP theorem, “Climate or Economy: pick half of one”. That is, if we continue business as usual, and even mine more coal, drill for more oil, etc. we’d be able to keep the economy hobbling along, though peak oil will probably prevent significant economic growth, and we’d fry the climate beyond all repair and that would in the medium and long term cause the economy (and civilization) to collapse. On the other hand, if we downshift demand massively, then the consumer-driven economies of the world will go into a massive (though hopefully temporary) depression, and we’ll still have to deal with warming that’s already in the pipeline. (Not to mention the particulates issue, which is a nasty double-bind in which ending coal use causes warming by removing light-reflecting soot.) Despite these both being bad, the latter still seems like the better one.
I’m in agreement with many prominent thinkers that the right way to approach this problem is to decrease demand by putting a price on carbon. But that’s hoping for a political settlement that may or may not happen in the time we have. As such, I can’t help but feel that we as individuals can and should do more, say in the form of local terraforming that I wrote about previously.
So, in that spirit, I want to answer the following (surely not novel) questions. How many trees would I need to plant to make up for the carbon I directly or indirectly put into the atmosphere? How many trees would we, collectively, as humans on Earth, need to plant to at minimum consume the carbon we put into the atmosphere on an ongoing basis? In other words, what’s my personal, and our collective, tree debt to the planet? (And this is just the Carbon-centric view. Planting trees has so many other benefits: restoring local ecosystems for other plants, and for animals and fungi, holding water in the soil, restoring soil structure, providing food for humans and non-humans, providing shade, regulating local temperatures, restoring natural beauty, etc.)
I’m sure there are good official estimates someplace, but let’s do a simple back of the envelope calculation. Let’s say that a mature tree (say an oak) absorbs about 10 kg of Carbon each year (I’ve seen figures both higher and lower than this, but in this range), and that its lifespan is in the hundreds of years (effectively forever for our current discussion). And for simplicity let’s ignore the sapling phase in which the tree is small and thus isn’t really absorbing as much Carbon annually.
Currently humanity is emitting over 10 billion tonnes (metric) of Carbon each year. That’s 1 trillion trees worth of Carbon absorption. (I’ve looked for estimates of the number of trees on Earth, and haven’t found a good source. I’ve seen huge ranges in estimates, from 1-200 trillion trees on Earth.) Let’s say that each of the 7 billion people on Earth were to plant trees, over the next 10 years. That works out to 14 trees per person, per year for the next 10 years. That’s not bad—about one a month! Of course given that some of us use far more energy than others, we should be planting more trees than that. (Using the 80-20 rule—that is, 80% of the Carbon is caused by 20% of the people and therefore so should the tree planting—it works out to 800 billion trees over 10 years by 1.4 billion people or about 57 trees per person per year.)
Our lived environments have lots of empty, degraded land in need of restoration. On some, or maybe even much of it local terraforming will be required if trees are to live there in the long term without ongoing human effort. (For example, swales might be required in arid and semi-arid areas to ensure sufficient soil moisture.)
In summary: if you use a lot of energy (live a Western lifestyle), plant a tree a week. If you don’t use much, plant a tree a month. This won’t resolve the many other environmental and energy challenges we face, and won’t halt climate change unless everyone does it, but it’s the least we can do to pay back our tree debt.