We can conclusively solve our climate change problem with a massive global reforestation campaign. This piece is a quick 2-minute summary, go here for a more in-depth overview with technical details.

Here is how:

First, the basic unit of CO2 is a “ton.” A billion tons is a gigaton. Each year, the world emits about 45 billion tons, or 45 gigatons of CO2.

We know that forests absorb CO2. How much? An acre of forest absorbs about 15 tons of CO2 in a year. Other tree species absorb somewhat more or less, some of them a lot more.

This means we need 3 billion acres of forest to offset our entire worldwide CO2 emissions each year.

Does the world have this much land for new forest?

Yes, but we will need to regreen deserts. There are about 4.7 billion acres of desert available, and we’ll only need about 3 billion of that. People have been successfully regreening deserts for decades, e.g. in China, Jordan, UAE, and Israel.

The limiting factor to regreening a desert is irrigation. We have to irrigate the trees for about 20 years until the vegetation changes the climate and induces its own rainfall.

We cannot rely on existing freshwater supplies, as they are all spoken for (food, agriculture, etc), so the only other source is desalination of seawater. This is energy-intensive, so our energy sources need to be low or zero-carbon —solar, for instance.

On a per-acre basis, the cost to build a solar array sufficient to power the desalination needed to irrigate that acre of forest for 20 years is about $1000/year per acre.

Thus, to reforest 3 billion acres at current prices will cost the world an investment of $3 trillion/year for 20 years.

That sounds like a lot, but the world GDP of 2017 was $80 trillion.

Therefore, this plan would require an investment of a little less than 4% of world GDP every year for 20 years. Combined with even moderate and gradual reduction in fuel emissions, we would effectively offset all CO2 emissions within 20 years once the forests reach maturity.

If we were to reforest the remaining 1.7 billion acres, the excess sequestration capacity would remove all of the CO2 remaining in the atmosphere that we have emitted since 1750 (beginning of the Industrial Revolution) in under 35 years.

This geoengineering plan is the lowest-cost, lowest-risk, most politically feasible, and requires the least risky technology to accomplish.

It is the solution most likely to work, and the only question is how long we will wait until we implement it.