Let's Plant Trees!

The idea has come up that we can solve global warming by planting "a trillion trees". The original study figured this would take about 3.5 million square miles, but it turns out that that will not be enough trees to absorb all the carbon dioxide the human race is expected to emit this century. We will need 16 trillion trees, requiring 56 million square miles of land. So fine, let's get to it!

There are 57.5 million square miles of land on the planet, 14 million square miles of which is already forested. We'll have to genetically engineer trees that can grow in the Sahara Desert, when planted in solid ice in Antarctica and Greenland, and when planted on land that is currently paved over. The whole human race will have to move out from land to sea colonies, and all farming will have to go offshore, too. This still leaves us with a shortfall of 12.5 million square miles, but if we fill in the Indian Ocean with soil, that will give us another 27 million square miles, which will be more than enough.

An optimistic estimate of the cost of planting a tree is $0.30 per tree, or $4.8 trillion, though costs will probably be higher that for planting the genetically engineered trees on sand, ice, and pavement. It would take a lot of time for the newly planted trees to grow large enough to be aborbing much CO2, so this would have to be done immediately. The US federal budget for 2018 was $2.5 trillion, but this is such a great idea that we can expect other countries to gladly chip in.

Once these trees have matured, it will be necessary to bury them, and deep, so that no methane from their decomposition can reach the atmosphere. This will cost at least $500 per tree, or $8 quadrillion for all the trees, or 91 times current world GDP, but this won't have to be done for several decades, so hopefully some technological breakthrough can make this process cheaper by then.

There will be a lot of disruption to people's lives when they all have to move out to giant sea colonies and change their diet to eating nothing but seafood, but we must not lose sight of the fact that we will have achieved our highest priority, which is that the combustion of fossil fuels should not be hindered in any way!

This article in Science magazine in the summer of 2019 was very optimistic about what could be achieved by planting trees, but it failed to mention one important point -- the idea was to plant trees in addition to curbing the rate of fossil fuel combustion. But since then, Republicans have seized on the idea and have been talking about planting the trees instead of curbing combustion.

Upon hearing that people were using his study to justify planting trees rather than curbing fossil fuel combustion, co-author Tom Crowther said "If tree planting is just used as an excuse to avoid cutting greenhouse gas emissions or to further limit environmental protection, then it could be a real disaster.".

The original study was based on using artificial intelligence to examine photos from Google Earth, so they really had no idea who owned this 3.47 million square miles they were talking about foresting, or how these owners felt about this idea. Furthermore, they admitted that some of the land in question was already in use for cattle grazing, which would have to end if the land was to be forested.

A few months after the original study came out, there was this response in the same magazine, which pointed out that the original study was riddled with over-optimistic assumptions and outright errors, concluding "The claim that global tree restoration is our most effective climate change solution is simply incorrect scientifically and dangerously misleading.". So we estimate that the cooling effect of an acre of planted trees was about half of what had been originally calculated.


The original, optimistic paper asserted that planting 0.9 billion hectares (3.47 million square miles) of forest would absorb 205 gigatonnes of carbon, which we corrected to about half that, or 102.5 gigatonnes, which corresponds to 376 gigatonnes of CO2, which corresponds to 108,000 tons of CO2 sequestered per square mile of forest.

If we make no attempt to curb the combustion of fossil fuels, the human race is expected to emit 6.1 trillion tons of CO2 by 2100. That much CO2 divided by 108,000 tons per square mile gives us 56 million square miles needed to plant new forests on. All the land on the planet is 57.5 million square miles, minus existing forests (14 million square miles), leaves us with 43.5 million square miles to plant our new forests in, meaning a shortfall of 12.5 million square miles. Filling in the Indian Ocean with soil would provide another 27 million square miles, more than enough.

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Bill Chapman