Everyone knows that to help mitigate the ongoing climate crisis, we need to plant new trees. A paper recently published in Science estimates that the Earth could support an additional 9,000,000 sq km of forest, potentially hosting 500 billion trees capable of capturing more than 200 billion tonnes of carbon dioxide at maturity. It would be a serious help.

The Earth’s landmass is 149,000,000 sq km. Take out glaciers (15 million) and deserts (28 million), and we are left with 104,000,000 sq km. Subtract cities (1.5 million), freshwater (1.5 million), forests (39 million) and shrubs (1 million) and we finally get 51,000,000 sq km of arable land, badly needed to feed 7.5 billion human beings.

Very few people are aware of the immense complexity of the whole system. ‘Widespread use at the scale of several millions of square kilometres globally of tree-planting and bioenergy crops’ – reads a leaked IPCC draft report – ‘could have potentially irreversible consequences for food security and land degradation’. In other words, more extensive monocultures and more bioenergy crops, fuelled by more fertilisers, could erode soil and its capacity to soak up carbon. Bioenergy has now a 50 per cent share of the world’s renewables consumption, according to Fatih Birol, executive director at the Institue of Economic Affairs: ‘as much as hydro, wind, solar and all others combined’. It’s good news, but not entirely. If we add the fact that increasing desertification and rising ocean levels (both propped up by greenhouse gases in the atmosphere) will take away more arable land, we arrive at a crucial ‘trilemma’. Should we use our spare soil for agriculture, reforestation or bioenergy?

Such a question would make sense in a multilateral, concordant world;  not on a planet where the president of the richest country scraps an environment-saving treaty, thus encouraging the president of the most tropically-forested nation to unleash a tree-cutting spree. 

Last year, 36,000 sq km of forest was felled. Wouldn’t it be better to start by stopping deforestation altogether? Animal farming takes up 77 per cent of the world’s arable land and provides us with 18 per cent of the calories. Shouldn’t we globally cut back on meat consumption? Modern bioenergy (such as liquid biofuel from bagasse, or biogas from residues) is already available. Shouldn’t we banish first-generation biofuels, which are distilled from food crops?

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