It’s clear that offsets are playing a large and growing role in climate policy, from the individual to the international level. In our view, they need to be backed by the best available science.

Our study used satellite data to track carbon levels, tree harvesting rates and tree species in forest offset projects compared with other similar forests in California.

Satellites offer a more complete record than on-the-ground reports collected at offset projects. That allowed us to assess all of California since 1986.

From this broad view, we identified three problems indicating a lack of climate benefit:

Carbon isn’t being added to these projects faster than before the projects began or faster than in non-offset areas.

Many of the projects are owned and operated by large timber companies, which manage to meet requirements for offset credits by keeping carbon above the minimum baseline level. However, these lands have been heavily harvested and continue to be harvested.

In some regions, projects are being put on lands with lower-value tree species that aren’t at risk from logging. For example, at one large timber company in the redwood forests of northwestern California, the offset project is only 4% redwood, compared with 25% redwood on the rest of the company’s property. Instead, the offset project’s area is overgrown with tanoak, which is not marketable timber and doesn’t need to be protected from logging.

Our research points to a set of recommendations for California to improve its offsets protocols.

One recommendation is to begin using satellite data to monitor forests and confirm that they are indeed being managed to protect or store more carbon. For example, it could help foresters create more realistic baselines to compare offsets against. Publicly available satellite data is improving and can help make carbon offsetting more transparent and reliable.

California can also avoid putting offset projects on lands that are already being conserved. We found several projects owned by conservation groups on land that already had low harvest rates.

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