Traditional cookstoves tend to burn fuel directly, whereas improved cookstoves are modified to burn fuel more efficiently. Improved cookstoves include "natural draft" (stoves with structural modifications to passively enhance airflow), "forced draft" (stoves with an external fan to actively drive air into the combustion chamber) and "gasifier stoves", which have a secondary combustion chamber.

Currently, carbon markets compare cookstoves by assessing the amount of fuel they burn and estimating the amount of carbon dioxide they produce. But this form of comparison is simplistic and misses the impact of black carbon, organic carbon and carbon monoxide. "Two stoves that have the same fuel efficiency savings, but don't have the same combustion efficiency, would look the same under a carbon-dioxide-only protocol, but would look very different when other emissions are considered," said Jennifer Burney from the University of California in San Diego, US.

Using recent cookstove emissions measurements, Burney and her colleague Luke Sanford estimated the actual radiative forcing impacts of traditional and improved cookstoves, and compared their findings with the protocols used by carbon markets. The researchers found that all improved cookstoves reduce emissions, but that "forced draft" stoves stand out for their reduced climate impact. "Our findings indicate that switching to forced-draft stoves would result in twice as much emissions reduction as some other stoves," said Burney. "These are big deals when you start to consider national-scale cookstove programmes and large-scale financing with carbon markets."

However, under the simple carbon dioxide calculation currently used by carbon markets, the advantages of "forced-draft" stoves are not nearly as apparent, showing only half the climate benefit compared to the more comprehensive calculation. "We show that current protocols underestimate the climate value of many improved cookstoves and fail to distinguish between technologies with very different climate impacts," Burney and her colleagues write in Environmental Research Letters (ERL).

The scientists hope their findings will lead to a change in protocols, with full emissions profiles taken into account for all combustion technologies, not just cookstoves. Given the number of people that rely on cookstoves, the emissions savings and health benefits could make a significant difference.

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