Planting for an uncertain future

Tree planting is still the best way to remove carbon: a new Exeter University study argues that in conditions of extreme climate uncertainty, the rewards of tree planting outweigh the risks.

Governments worldwide have pledged to expand tree cover to remove greenhouse gases, with the UK committing to plant 30,000 hectares of trees each year until 2050.

However, environmental economists point out that there are significant risks that come with converting farmland to forests in a future of climate change and economic uncertainty.

These include the risk of large-scale tree planting displacing agriculture and impacting food security, depending on where it takes place.

In a study in Proceedings of the National Academy of Sciences (PNAS), the researchers use the UK as an example to demonstrate that uncertainties about climate change and the economy make the difficult trade-off between carbon removal and agriculture even trickier.

Frankie Cho, a PhD graduate from the University of Exeter and lead author of the study, explains: “One problem is that, because it is unclear what countries round the world will do to tackle climate change – we don’t know how challenging the climate will be in the future. If climate change is extreme, broadleaf trees in southern UK offer the best carbon removal – but that’s prime farmland and could be really costly under certain economic futures.

“If climate change is milder, planting conifers on less productive land makes more sense, but those trees will not grow well if conditions are more extreme. The problem is that we don’t know what the future holds and can’t be certain which type of trees we need to plant and where.”

However, using recent advances in the theory of decision-making under uncertainty, the researchers show that despite these risks tree planting can still be the most cost-effective way to remove carbon.

Their study shows that a ‘portfolio’ approach to tree planting – diversifying species and planting locations – helps balance risks and moves beyond planting strategies that simply hope that everything will be okay.

This strategy minimises the danger of betting on the wrong future, ensuring tree-planting decisions remain resilient in the face of uncertain future climatic and economic conditions.

Importantly, they show that if policymakers adopt these portfolio approaches to tree-planting, it becomes a far more cost-effective strategy for carbon removal than alternatives like biomass energy with carbon capture and storage or direct air capture technologies.

Co-author of the study Professor Brett Day, from the University of Exeter, added: “We don’t have any other option that can remove carbon from the atmosphere at the scale and cost that we need to meet our Net Zero targets. While tree-planting carries risks, our study shows that, if done strategically, it remains the best solution we have.”

With thanks to the University of Exeter, authors of the study Resilient tree-planting strategies for carbon dioxide removal under compounding climate and economic uncertainties, published in Proceedings of the National Academy of Sciences. This article first appeared in the 82nd Issue of ITF’s journal, Trees.