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Carbon Offsets From Clean Cookstoves Are Kind of Bogus, Too

A new study from the University of California, Berkeley, breaks down the issues, while also stirring up a controversy of its own.

Cooking on an open flame.
Heatmap Illustration/Getty Images

A new study casts doubt on the integrity of yet another type of carbon offset.

Researchers from the University of California, Berkeley, investigated clean cookstove projects, in which companies distribute stoves that require less or cleaner types of fuel to people who cannot afford them and sell carbon credits based on the resulting emission reductions. These projects have generated, on average, nine times more carbon credits than they should have based on their climate benefits, the researchers found.

This kind of credit inflation obscures climate progress, as the individuals and businesses who buy these credits do so to justify their own emissions under the belief that they are funding climate action elsewhere.

It also threatens a key source of funding to remedy a major public health problem. Nearly a third of the global population — some 2.3 billion people — cook with wood and charcoal burned on open fires or in very basic stoves that expose people to dangerous levels of pollution, including particulate matter and carbon monoxide. The smoke contributes to respiratory and cardiovascular problems and leads to an estimated 4 million premature deaths every year. On top of that, this form of cooking releases roughly 2% of global greenhouse gas emissions.

Companies have jumped at the opportunity to finance solutions by selling carbon offsets, with great success. Between 2017 and 2022, the volume of finance secured for clean cookstoves through the carbon market increased 45-fold, according to a report by the Clean Cookstove Alliance published last fall. Now, cookstove projects make up some 10% of all credits on the carbon market. And they’re one of the fastest growing types of offset projects.

The new study, published in the peer-reviewed journal Nature Sustainability on Wednesday, finds that the methods developers are using to measure the amount of carbon these projects avoid are deeply flawed.

The first red flag the researchers identified was that academic studies of clean cookstoves report much lower adoption rates (whether the new stove was used) and usage rates (how often the new stove was used) than offset projects do. A representative sample of offset projects reported an 86% adoption rate and 98% usage rate, whereas the research literature reported a 58% adoption rate and 52% usage rate.

“The literature at large has found, honestly, devastatingly low rates of adoption and usage,” Annelise Gill-Wiehl, a PhD student at Berkeley and the lead author of the study told me. Some families totally abandon their new stoves, while others continue to use traditional cooking methods in addition to the clean stove. That’s because the new stoves might have smaller burners, not get as hot, change the taste of traditional foods, or else just create more work for cooks. “The first thing you have to ask yourself is, have these offset projects just solved it?” Gill-Wiehl said. “Or are there limitations in their methods?”

One big limitation, according to Gill-Wiehl and her coauthors, is the way offset data is collected. To measure adoption, many project managers use a simple one-time survey that asks households if they used the new stove in the last week or month. If they reply yes, the developer will generate credits as if the household used the stove 100% of the time. Not only is this not exactly robust methodologically, but it may also result in participants inflating their usage to please the survey collectors — a common effect known as “social desirability bias.”

Another major issue stems from the way these projects account for larger environmental impacts. One of the key ways clean cookstove initiatives cut emissions is by reducing the degradation of forests that results from the gathering of fuel to make fires. It would be impossible to measure these cuts directly, but the default estimates that project developers use vastly overstate the level of degradation that would otherwise occur compared to what the peer-reviewed literature has found.

But like anything offsets-related, this study, too, has attracted fierce scrutiny. After an earlier version of it was published a year ago, offset project developers responded with an open letter calling it “misguided.” For instance, the letter calls it inappropriate to compare carbon offset projects to non-commercial projects analyzed in the academic literature. It also accuses the Berkeley researchers of selectively choosing studies and carbon offset projects to include. Finally, the letter also points to the fact that the Better Cooking Company, a cookstove company that is trying to sell credits, provided funding for the study and asserts that the findings benefit that company.

Gill-Wiehl pushed back on all points. The Better Cookstove Company provided less than 5% of the funding, she said, and had no influence over the findings. She added that the results didn’t benefit the company — the study implied that it, too, was guilty of over-crediting, primarily due to inflated forest conservation estimates. (The Better Cookstove Company has since updated its forest conservation estimates to align with the findings in the study, decreasing its sellable credits.)

“We did not write this to burn cookstoves to the ground,” she told me. “This is an incredibly important project type, and it’s so incredibly important that it can't be based on a house of cards.”

Gill-Wiehl said she and her co-authors want the carbon market registries — the groups that design the methodologies project developers must follow to generate and sell credits — to adopt stronger rules that improve the integrity of the market. For example, to measure usage, they could require developers to collect metered data from the stoves or to use fuel sales data. They also want the registries to require that developers use more accurate estimates from the literature for forest degradation. Without significant change, buyers could lose confidence and funding could dry up.

Some of the issues with clean cookstove projects were already known, if not quantified to the extent in this new paper, and there are some ongoing efforts in the industry to improve them. An influential United Nations body recently supported research to establish more accurate estimates of forest degradation, and a consortium of government groups and NGOs is working to develop stronger rules for crediting cookstove projects.

The authors of the study hope this increased attention on cookstoves doesn’t just lead to more legitimate offset projects, but also to ones that better prioritize public health. The vast majority of the cookstoves handed out for offset projects are designed to run more efficiently, but still expose users to dangerous levels of pollution. As of November 2022, only 4% of projects provided the types of stoves that the World Health Organization deems “clean for health at point of use.”

“I feel like at this moment when there’s a shake up of the offset market in general — but also, right now around cookstoves — we have an opportunity to direct all of this finance to projects that have a transformative benefit to people’s lives and health,” Barbara Haya, director of the Berkeley Carbon Trading Project and one of the study’s authors, told me. “And we have an obligation to do that if we’re going to use those credits to make claims of reducing emissions.”

Editor’s note: This story has been updated to correct the proportion of funding the Better Cookstove Company provided for the study and to reflect changes the company has made to its offset methodology since the study’s completion. We regret the error.


Emily Pontecorvo

Emily is a founding staff writer at Heatmap. Previously she was a staff writer at the nonprofit climate journalism outlet Grist, where she covered all aspects of decarbonization, from clean energy to electrified buildings to carbon dioxide removal. Read More

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