A new paper by leading climate scientists and policy experts finds that indirect greenhouse gases account for roughly 15% of current global warming from human emissions yet remain largely absent from climate policy. These overlooked pollutants, including carbon monoxide, non-methane volatile organic compounds, nitrogen oxides, and molecular hydrogen, do not warm the climate directly. Instead, they alter atmospheric chemistry in ways that increase levels of methane, ozone, and other greenhouse gases, which results in increased warming. Reducing these emissions represents an overlooked opportunity to slow warming while delivering air quality benefits.

Using 20 years of satellite-derived data on wildfire severity and smoke particulate matter from California, Iván Higuera-Mendieta and Marshall Burke conclude that low-severity fires – a proxy for prescribed burns – can significantly reduce the probability of very high severity wildfires for a decade. The smoke particulate pollution produced by these less severe fires is outweighed by the reductions in future smoke from wildfires as a result. The researchers’ modeling suggests that sustained treatment of 500,000 acres annually in California with prescribed burns would reduce cumulative harmful smoke pollution by about 10% over a decade. The findings by Higuera-Mendieta and Burke fill an important data gap about potential air quality tradeoffs associated with prescribed burns. The effects measured in the study are most impactful in the state’s conifer forests, the researchers found. A policy that applies prescribed burning for up to 1 million acres/year in California conifer forests would yield cumulative benefits in terms of smoke reduction that exceed the costs of the added smoke from the initial prescribed burning “in as early as two years, with benefits exceeding costs by at least three-fold a decade after project initiation,” the authors write.

Most people have experienced a heat wave on land. But heat waves can strike in the ocean too. Researchers say a controversial strategy to shield Earth from some of the sun’s rays would offer unequal protection for the oceans and communities that depend on them, leaving 25% to 75% of the world’s seas still at risk from overheating.