Could One Trillion More Trees Stop Global Warming?

The latest panacea to stop global warming is to plant trees, lots of trees. An Associated Press story by Seth Borenstein, printed on the front page of the July 5, 2019, Arizona Daily Star suggests that one trillion new trees will do the job. As an aside, I regard Borenstein as a propagandist rather than a journalist, in part, because he often refers to carbon dioxide emissions as “carbon pollution” even though carbon dioxide is necessary for life on earth (See my article: Carbon dioxide is necessary for life on Earth).

The story is based upon a press release from EurekAlert! which summarizes research from The Crowther Lab at ETH Zurich. The researchers estimate that planting enough trees, an amount equivalent to covering the entire United States, would suck up “two thirds of the 300 billion tonnes of carbon that has been released into the atmosphere as a result of human activity since the Industrial Revolution.” “The researchers calculated that under the current climate conditions, Earth’s land could support 4.4 billion hectares of continuous tree cover. That is 1.6 billion more than the currently existing 2.8 billion hectares.” “The study also shows which parts of the world are most suited to forest restoration. The greatest potential can be found in just six countries: Russia (151 million hectares); the US (103 million hectares); Canada (78.4 million hectares); Australia (58 million hectares); Brazil (49.7 million hectares); and China (40.2 million hectares).”

I have some questions/reservations about this unnecessary scheme:

1. How much water will be needed to grow one trillion trees, and where will the water come from?

2. Will not large areas of forest decrease the albedo of the planet, i.e., increase the amount of sunlight absorbed rather than reflected, and thereby heat the surface?

3. Through the process of evapotranspiration, trees add water vapor to the air. Water vapor is a much stronger green-house gas than carbon dioxide. Could this itself cause more warming?

These questions are not addressed in the research.

See also:

Evidence that CO2 emissions do not intensify the greenhouse effect

The Broken Greenhouse – why CO2 is a minor player in global climate

An examination of the relationship between temperature and carbon dioxide