New forests as climate saver?

Afforestation of 900 million hectares of forest could swallow two thirds of CO2 emissions

Forests are important CO2 killers - and there is enough space on earth to reforest 900 million hectares of forest. © Xurzon / iStock
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Space enough: Worldwide, about 0.9 billion hectares of land could be reforested to new forests - without having to give way to fields or settlements, as a study reveals. However, the deciding factor is that, according to the researchers, this additional forest area is sufficient to swallow two-thirds of man-made CO2 emissions. Forest conservation and afforestation could thus be one of the best solutions for climate protection, according to the researchers in the journal "Science".

Forests are not only the "green lung" of our planet - they also act as buffers in the climate system. The roughly three trillion trees worldwide absorb CO2 and thus contribute to reducing the CO2 content of the atmosphere. However, forest fires, deforestation and the fragmentation of tree populations increase the forests and also reduce their CO2 intake. Forest protection and afforestation have therefore long been considered an important part of climate protection efforts.

But how big would the climate effect of targeted reforestation be? And how much room would there be for this on the earthly land? The IPCC estimated in its latest World Climate Report that with around one billion hectares of additional forest, global warming could be reduced to 1.5 degrees by 2050. But reforestation is not everywhere possible: many regions are too cold or too dry, others are needed for agricultural land, settlements and other human activities.

How much forest is there - and where is there still air?

Concrete figures are now provided by Jean-Francois Bastin of the ETH Zurich and his colleagues. For the first time, they have identified where on earth the potential for additional forest land exists. To do so, they evaluated data on nearly 80, 000 forests worldwide and initially mapped the existing forest stock. Then they used climatic data to determine which areas of additional forest could grow.

The result: "In principle, the terrestrial land area could produce forests with 4.4 billion hectares of crown area under the existing climatic conditions, " report Bastin and his team. "That is 1.6 billion hectares more than exists today." However, the areas that are needed for agriculture and settlements worldwide have to be taken away from it.
"Because these areas are needed to sustain the growing world population, " emphasize the researchers. display

Free space as big as the USA

However, this means that 0.9 billion hectares of land remaining for afforestation and forest regeneration will remain in the world this corresponds approximately to the area the USA. There would be enough space on our planet for additional CO2 sinks. Many of these potential afforestation areas are also located in areas that have previously been deforested by forests, storms or other events, while other areas still have only a sparse tree population that could be densified

The map shows the areas available for reforestation worldwide. Bastin et al. / ETH Zurich

But where are these potential forest areas? "More than half of this potential is spread over only six states, " report Bastin and his colleagues. 151 million hectares could be afforested in Russia in this country enormous forest areas have been destroyed by fire in recent years. Another 103 million hectares are in the US and 78.4 million hectares in Canada. Australia could contribute 58 million hectares and China 40.2 million hectares.

Enough for two thirds of CO2 emissions

But what good is that for climate protection? For this, the researchers calculated how much CO2 the additional forest areas could absorb. The result: "We estimate that the vegetation in these reforestation areas could save an additional 205 billion tons of carbon, " they report. According to them, this corresponds to about two-thirds of the roughly 300 gigatonnes of carbon that humanity has emitted into the atmosphere as CO2 since the Industrial Revolution. However, according to other calculations, this anthropogenic carbon load is significantly higher.

"Our study clearly shows that afforestation is currently the best available solution to climate change, " says co-author Tom Crowther of ETH Zurich. "And it is a climate solution that we can all contribute to: everyone can plant trees, donate for forest regeneration or invest money in climate-friendly companies."

Race against time

However, time is pressing, as Crowther emphasizes: "We need to act quickly, because it will take decades for forests to mature and exploit their potential as natural CO2 storage. "In addition, the loss of existing forests continues to progress. Especially in the Brazilian Amazon Rainforest and in Southeast Asia more and more forest areas are being destroyed to make room for pastures or plantations.

"From a climate perspective, therefore, both are important. Avoiding deforestation so as not to increase emissions and afforestation in order to bind carbon from emissions, "Karlheinz Erb from the University of Natural Resources and Applied Life Sciences in Vienna commented on the study. This is important, in his view, because the authors did not take into account all limiting factors in their estimate of available afforestation areas. For example, there is a lack of increasing demand for arable land or the use of wood by the growing world population.

"It follows that afforestation is probably not a miracle weapon, but must be part of a solution, " says Erb. Felix Creutzig from the Mercator Research Center also sees things in a similar way: "In spite of its potential, afforestation can only be one of many measures for climate protection. A rapid departure from the fossil economic model is necessary. "(Science, 2019; doi: 10.1126 / science.aax0848)

Source: ETH Zurich, AAAS

- Nadja Podbregar