Last week I wrote an article in which I suggested planting trees as potentially a much cheaper way to slow or even reverse global warming, cheaper, that is, than a carbon tax. I wrote:

The third low-cost way to rein in global warming is by planting trees. Trees absorb and store CO2 emissions. You could call the tree-planting strategy geo-engineering, but it would count as such in a very low-tech form. According to a July 4, 2019 article in The Guardian, planting one trillion trees would be much cheaper than a carbon tax and much more effective. At an estimated cost of 30 cents per additional tree, the overall cost would be $300 billion. That’s large, but it’s a one-time cost. Moreover, writes The Guardian’s environment editor Damian Carrington, such a tree-planting program “could remove two-thirds of all the emissions that have been pumped into the atmosphere by human activities, a figure the scientists describe as ‘mind-blowing’.” A carbon tax, by contrast, would simply slow the rate of emissions into the atmosphere.

Yesterday I came across this CNN news story from July 30.

Ethiopia planted more than 353 million trees in 12 hours on Monday, which officials believe is a world record.

The burst of tree planting was part of a wider reforestation campaign named “Green Legacy,” spearheaded by the country’s Prime Minister Abiy Ahmed. Millions of Ethiopians across the country were invited to take part in the challenge and within the first six hours, Ahmed tweeted that around 150 million trees had been planted.

“We’re halfway to our goal,” he said and encouraged Ethiopians to “build on the momentum in the remaining hours.” After the 12-hour period ended, the Prime Minister took to Twitter again to announce that Ethiopia not only met its “collective #GreenLegacy goal,” but exceeded it.

Hmm. Let’s round 353 million trees down to 333 million. That’s one third of a billion. My article said that we need about 1 trillion. So during that one 12-hour period, volunteers in one country achieved 1/3000 of what was needed. Imagine that 50 times as many volunteers in other countries were as efficient as the Ethiopians. In a 12-hour period, they could plant 50 times 1/3000 or 1/60 of what is needed. So all we would need is 60 such 12-hour periods per person. Stretch that out over 3 years, and it means volunteering to take one long day to plant trees 20 times a year for 3 years.

Of course, that’s not the least-cost way. Far cheaper would be for millions of rich people like me and a number of our readers in rich countries to put up, say, $500 each, and hire low-income people in poor countries to do it. I won’t bother working out the math, but you can see this is not a very expensive proposition. And if you think it is expensive, compare that to the amount of high-value time spent arguing and lobbying for (and against) a carbon tax.