In recent weeks, a new study by researchers at ETH Zurich has hit the headlines worldwide (Bastin et al. 2019). It is about trees. The researchers asked themselves the question: how much carbon could we store if we planted trees everywhere in the world where the land is not already used for agriculture or cities? Since the leaves of the trees extract this carbon in the form of carbon dioxide – CO2 – from the air and then release the oxygen – O2 – again, this is a great climate protection measure. The researchers estimated 200 billion tons of carbon – provided we plant over a thousand billion trees.

The bang effect of the new study was mainly based on the statement in the ETH press release that trees could use it to offset two thirds of the man-made CO2 pollution to date. To be able to largely compensate for the consequences of more than two centuries of industrial development with such a simple and little controversial measure – that sounds like a dream! And was immediately welcomed by those who dream of climate protection that does not hurt anyone.

The study by ETH researchers has another important result that has hardly been reported. Without effective climate protection, progressive warming will lead to a massive loss of existing forest cover, especially in the tropics. At the same time, the models are not yet able to make reliable statements on how forests can cope with new extremes, fire, thawing permafrost, insects, fungi and diseases in a changing climate.

The massive planting of trees worldwide is therefore a project that we should tackle quickly – not with monocultures but carefully, close to nature and sustainable. But we must not give in to any dreams about how many billions of tons this will bring. And certainly not the illusion that you could take more time to abandon fossil energy use. On the contrary, we need a rapid end to fossil energy use precisely because we want to preserve the world’s existing forests.