A recent paper in Science (West et al. 2023, pdf available here) reviewed the effectiveness of projects intended to reduce greenhouse gas emissions by avoiding deforestation, and the results were discouraging. One common way that carbon offsets work is by paying land managers to leave their forests in place, with their trees unharvested. This is called an “avoided deforestation” project and is a common way that carbon offsets are sold. In 2021, for example, the trading market for such projects was about $1.3 billion.
The authors found that most of the projects they assessed failed to reduce deforestation, meaning that even though they were sold as a means of offsetting carbon emissions elsewhere in the world, the carbon associated with logging these forests was still released into the atmosphere. And even for the projects that reduced deforestation, the reductions were much lower than initially claimed when the offsets were sold. The projects that they looked at were all in tropical forests in Peru, Colombia, the Democratic Republic of Congo, Tanzania, Zambia, and Cambodia. Of these countries, Peru had the best record of successfully avoiding deforestation – half of their projects had a discernible effect. There was no evidence that the African projects were successful, and success was poor in Colombia and Cambodia.
Additionally, the effectiveness of the projects, even in Peru, was far less than was hoped before the projects, and far less than the project managers claimed. In the end, 71% of the offsets sold from these projects had no significant effect on deforestation. Of the remaining offsets (29%), the impact on reducing deforestation was so marginal that they only had the emissions-reducing equivalency of about 6% of the overall projects. Essentially, for clients who bought those emissions offsets, they only got about 6% of the intended effect. This is like paying for a gallon of milk and getting a little less than a cup. Except that in this case, the point isn’t to have milk to drink; the point here is to prevent worsening an ongoing crises. For anyone trying to use these offsets, unfortunately, the crisis was not averted.
The authors don’t point to many potential solutions, noting only that with greater scrutiny and monitoring, perhaps only validated projects should be traded in voluntary carbon markets. I agree that more rigorous assessment of project performance is crucial. And this study also indicates that other approaches than avoided deforestation carbon offset projects will be necessary to address climate change.