We can conclusively solve our climate change problem with a massive global reforestation campaign.

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.