Planting 1 Billion Hectares of Forest Could Help Check Global Warming

Note to Reader:

Today, the only technology capable of absorbing CO2 is photosynthesis. Planting trees is the most efficient, pragmatic, democratic and least expensive way to mitigate the carbon impacts of climate change. Trees would also be a cornerstone strategy for adapting to seasonal changes in the water balance. In the British Columbia context, an intact urban tree canopy would intercept half the annual precipitation.

The latest report from the United Nations’s Intergovernmental Panel on Climate Change recommended adding 1 billion hectares of forests to help limit global warming to 1.5° C by 2050. Ecologists Jean-Francois Bastin and Tom Crowther and their co-authors wanted to figure out whether today’s Earth could support that many extra trees, and where they might all go. Bastin et al are researchers at the Crowther Lab, based at the Swiss Federal Institute of Technology in Zurich

Bastin and Crowther determined that around 0.9 billion hectares of land worldwide would be suitable for reforestation, which could ultimately capture two thirds of human-made carbon emissions. This land area would be equivalent in size to the United States. It would translate to 1–1.5 trillion trees, adding to the 3 trillion trees already on Earth.

WHO IS THOMAS CROWTHER: After completing his doctorate in ecology at Cardiff University, Thomas Crowther switched to Yale University, where he studied the ecology of ecosystems, with a specific focus on soil. While in the USA, he came into contact with an organisation that is leading the United Nations “billion trees campaign”. But no one had a clue how many trees there actually were on the planet, so they couldn’t quantify the contribution of their efforts. Crowther was given the task of producing a global map of the world’s trees, which allowed them to discover the current population number. The study was published in 2015.

How many trees are there on Earth?

It’s a simple question: how many trees are there on Earth? The answer required 421,529 measurements from fifty countries on six continents. Now this new data has been combined to produce a stunning visualisation of our planet as never seen before.

“Our study shows clearly that forest restoration is the best climate change solution available today, and it provides hard evidence to justify the investment,” says Professor Thomas Crowther, Swiss Federal Institute of Technology

The Crowther Lab at the Swiss Federal Institute of Technology, Zurich, investigates nature-based solutions to climate change. In their latest study, the Crowther Lab researchers showed for the first time where in the world new trees could grow and how much carbon they would store.

Published in the journal Science, July 2019, the study shows that global reforestation would be the most effective method to combat climate change.

Thomas Crowther’s research mission is to develop a global understanding of the ecological processes that drive the carbon cycle and the climate. A deeper understanding is important for improving climate change forecasting.

To fulfill his mission, he has specialists from the fields of satellite remote sensing, genetics of soil-​dwelling organisms, ecology of biotic communities and experts in modelling Earth systems.

It was the tree count that drew international attention to Crowther.

“Communication was the trigger for everything. Even now, scientists are seldom encouraged to present their research in the public domain. If I hadn’t spent a lot of time doing so, no one would have known about my work,” says Thomas Crowther,  an assistant professor of ecology.

“Everyone is asking the ultimate question: what form will climate change take over the rest of this century, and how can we manage or conserve natural ecosystems to minimize these effects.

“If we understand how ecological processes are linked to the climate, we can also discover how to combat climate change through specific types of land use, for instance.”

The Potential for Global Forest Cover

The restoration of forested land at a global scale could help capture atmospheric carbon and mitigate climate change. Thomas Crowther’s team. used direct measurements of forest cover to generate a model of forest restoration potential across the globe.

Their spatially explicit maps show how much additional tree cover could exist outside of existing forests and agricultural and urban land. An additional 0.9 billion hectares of continuous forest would represent a greater than 25% increase in forested area, including more than 500 billion trees and more than 200 gigatonnes of additional carbon at maturity. Such a change has the potential to cut the atmospheric carbon pool by about 25%.

A Benchmark for Global Action

“The restoration of trees remains among the most effective strategies for climate change mitigation, states Dr. Jean Francois Bastin, lead author for the study.

“We mapped the global potential tree coverage to show that 4.4 billion hectares of canopy cover could exist under the current climate. Excluding existing trees and agricultural and urban areas, we found that there is room for an extra 0.9 billion hectares of canopy cover, which could store 205 gigatonnes of carbon in areas that would naturally support woodlands and forests.

“This highlights global tree restoration as our most effective climate change solution to date. However, climate change will alter this potential tree coverage. We estimate that if we cannot deviate from the current trajectory, the global potential canopy cover may shrink by ~223 million hectares by 2050, with the vast majority of losses occurring in the tropics.”

“Our study provides a benchmark for a global action plan, showing where new forests can be restored around the globe.. Action is urgent, and governments must now factor this into their national strategies to tackle climate change,” concludes Dr. Bastin.

The Best Available Solution

“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,” says Thomas Crowther, the study’s senior author and an assistant professor of ecology at the Swiss Federal Institute of Technology, Zurich.

“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.”

Canada is #3 for Reforestation Potential

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).

Many current climate models are wrong in expecting climate change to increase global tree cover, the study warns. It finds that there is likely to be an increase in the area of northern boreal forests in regions such as Siberia, but tree cover there averages only 30 to 40 percent. These gains would be outweighed by the losses suffered in dense tropical forests, which typically have 90 to 100 percent tree cover.

This is where the world could support new forests. The map excludes existing forests, urban areas, and agricultural lands. J. BASTIN, ET. AL., SCIENCE 365, 76, 2019

To learn more about Tom Crowther, a ‘man on a mission’, click on the link below to watch a YouTube video.