

Photo by Crowther Lab / ETH Zurich

About 0.9 billion hectares (2.2 billion acres) of land across the world would be suitable for reforestation, that could ultimately capture two-thirds of human-made carbon emissions.

The Crowther Lab of ETH Zurich published a study in the journal Science that demonstrates it'd be the most effective method to fight climate change.

The Crowther Lab at ETH Zurich studies nature-based solutions to climate change. In their more recent study, the researchers showed for the first time ever where in the world, new trees could grow as well as how much carbon they would store.

The researchers estimated that under the current climate conditions, Earth’s land could support 4.4 billion hectares of constant tree cover. That’s 1.6 billion more than the existing 2.8 billion hectares. Of those 1.6 billion hectares, 0.9 billion hectares fulfill the criterion of not being used by humans. That means that there is currently an area of the size of the United States available for tree restoration. Once mature, those new forests could store 205 billion tonnes of carbon: approximately two-thirds of the 300 billion tonnes of carbon which has been released into the atmosphere as a result of human activity since the Industrial Revolution.

According to Professor Thomas Crowther, co-author of the study and founder of the Crowther Lab at ETH Zurich: “We all knew that restoring forests could play a part in tackling climate change, but we didn’t really know how big the impact would be. Our study shows clearly that forest restoration is the best climate change solution available today. But we must act quickly, as new forests will take decades to mature and achieve their full potential as a source of natural carbon storage.”

This study also shows which parts of the planet are most suited to forest restoration. The most significant potential can be found in just six countries: Russia (151 million hectares); the United States (103 million hectares); Canada (78.4 million hectares); Australia (58 million hectares); Brazil (49.7 million hectares); and China (40.2 million hectares).

Several current climate models are wrong in expecting climate change to increase global tree cover, according to the study. There’s likely to be an increase in the area of northern boreal forests in regions such as Siberia, but tree cover there averages 30% to 40% only. These gains could be outweighed by the losses suffered in dense tropical forests, that typically have 90% to 100% tree cover.

A tool on the Crowther Lab website enables users to look at any point on the globe, and determine how many trees could grow there and how much carbon they would store. It also offers lists of forest restoration organizations. The Crowther Lab will also be present at 2019’s Scientifica (website available only in German) to demonstrate the new tool to visitors.

The Crowther Lab uses nature as a solution to: 1) better allocate resources – identifying the regions which, if restored appropriately, could have the most significant climate impact; 2) set realistic goals – with measurable targets to maximize the effects of restoration projects; and 3) monitor progress – to evaluate whether targets are being achieved over time, and take corrective action if needed.