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Cambridge Centre for Carbon Credits (4C)


Halting global deforestation via carbon credits: an overview of our approach in 4C

The world is facing two major crises: a climate crisis and a biodiversity crisis. While the former is now very familiar with the public, fewer people know about the latter. The biodiversity crisis refers to the dramatic loss of species globally due to human activities – the two most important of which are habitat loss and climate change. Preserving forests can help to tackle both these crises in conjunction – it prevents carbon dioxide from leaving the trees and retains biodiversity. Nowhere is this more important than in tropical rainforests, where a large fraction of the world’s biodiversity exists and which are still relatively intact habitats compared to other parts of the planet.

How do we prevent deforestation? We believe we need to pay for it - and carbon credits offer a mechanism to do this.

In this video series, Prof S. Keshav - computer scientist and co-director of 4C - explains how 4C is working to ensure that carbon credits for forest conservation and nature-based solutions can be assessed more accurately and made more trustworthy by considering the additionality, leakage and permanance of carbon storage in forests.

Calculating the "additionality" of deforestation avoidance interventions

When evaluating forest protection projects, the concept of additionality is crucial. A landowner might claim to have saved a patch of forest from destruction, and ask to be paid on that basis. However, it could be that the forest was not saved as a result of their actions – it might be that the forest was never going to be destroyed in the first place, whether that landowner managed it or not. We want to pay only for services rendered – for "additional' value conferred. How can we determine whether or not that was the case? It is impossible to prove what would have happened in the absence of an intervention, but we can gather evidence to make a case using counterfactual scenarios.

Explaining the leakage effect resulting from negative externalities in deforestation avoidance

Another integral and historically neglected concept in nature protection schemes is leakage. It might be that when you protect an area from deforestation, you simply displace any harmful activity from inside the protected area to neighbouring unprotected areas (local leakage). Or, for some internationally traded products, that activity could be shifted to an area on the other side of the world (global leakage).

How can we detect leakage? We can create a ‘buffer zone’ around the project area, normally around 5km radius, in which we also monitor deforestation using satellites. If we detect increasing deforestation in this buffer zone since the project began, then that implies that leakage is likely to have occurred. This can all be done from space using satellite imagery. At the moment we don’t have a fully defined solution to estimate global leakage.

Adjusting impermanent nature interventions to be equivalently permanent to geological sequestration

When it comes to carbon sequestration, there are two traditional categories. Permanent geological sequestration entails CO2 being pumped down into cavities in rock to form a layer of calcium carbonate. This method is quite effective and very long-term but it is expensive. The second category is nature-based solutions, like planting a tree. When a tree is planted, it locks down carbon in its tissue – both in the above ground biomass that we can see, and in the below-ground biomass, like roots. This type of sequestration is far more cost-effective and comes with many cobenefits for humans and wildlife, but it has a key disadvantage – it is impermanent. Eventually the tree will die, and much of that captured CO2 will be released back into the atmosphere. Does that impermanent sequestration of carbon dioxide still have value in the fight against climate change? How can we begin to measure what that value is? And how do we know how long that carbon dioxide will be sequestered for?


Prof S. Keshav is using computer science to move towards a sustainable future through clean energy and environmental conservation. He is a co-director of 4C - the Cambridge Centre for Carbon Credits - and the Robert Sansom Professor of Computer Science in the Department of Computer Science and Technology at the University of Cambridge.

Thanks for this summary text to James Miller, student environmentalist and film-maker.