Levels of a potent greenhouse gas are quietly spiking in the atmosphere and increasingly worrying environmental groups that say its use needs to be reined in if the US is to avoid climate catastrophe.
Furthermore, recent research has found the vast majority of the little-known gas, known as sulfuryl fluoride, is attributable to a state typically known for its climate-forward policies: California.
About 85% of US emissions of sulfuryl fluoride were traced by a recent peer-reviewed study to southern California, where the state’s $4.2bn pest-control industry uses it for drywood termite control. Sulfuryl fluoride is estimated to be up to 7,500 times more potent than carbon dioxide in terms of its greenhouse-gas potential.
The gas, which is also highly toxic, “has slipped under the radar”, said the Johns Hopkins University study co-author Dylan Gaeta, in large part because it only started to be widely used in recent years.
State regulators in 2023 rejected a petition calling for a sulfuryl fluoride phaseout, and Gaeta and others say the findings highlight the need for urgent regulatory action.
“Without some form of intervention, sulfuryl fluoride is going to keep accumulating in our atmosphere,” he added.
The US Environmental Protection Agency first approved sulfuryl fluoride in about 1960, but it was not used widely until methyl bromide, a common pesticide and powerful greenhouse gas previously utilized in termite treatment, was phased out about 20 years ago.
Sulfuryl fluoride is primarily used in structural fumigation in which a home is covered with a material the study’s authors likened to a circus tent. When the fumigation is complete, the gas trapped under the tent is simply released into the atmosphere. Sulfuryl fluoride is also used to kill pests in agricultural commodities that are shipped abroad to try to prevent the spread of invasive species.
But research has increasingly found the gas is not as safe as once thought, in large part because it stays in the atmosphere for about 40 years.
“It doesn’t have the same ozone-depleting problem as methyl bromide, but it has a long lifetime in the atmosphere, so over that time period it acts as a pretty potent greenhouse gas,” said Gaeta.
Average concentrations of sulfuryl fluoride in the atmosphere remain relatively low compared with carbon dioxide, but it is being released at levels faster than it breaks down. It stores heat energy at higher levels, and its presence in the atmosphere is 10 times greater than 50 years ago.
“There’s a heck of a lot less sulfuryl fluoride in the air than carbon dioxide, but one molecule of sulfuryl dioxide is much more potent than one molecule of CO2,” the study co-author Scot Miller said.
Toxicity is also a concern. Among other health issues, short-term exposure is linked to respiratory ailments, stomach pain, seizures, muscle twitching and other nervous system problems.
Exposure has killed some pest-control workers, as well as thieves who have broken into homes that are being fumigated, and long-term exposure is linked to cancer and cognitive damage. The study’s authors say their findings highlight the need for California and the EPA to include sulfuryl fluoride in their greenhouse-gas monitoring inventories.
The gas also is not included in global greenhouse gas reduction efforts, such as the Paris agreement, which were developed before sulfuryl fluoride was widely used.
Still, the California Air Resources Board (Carb) rejected a 2022 petition from the Center for Biological Diversity calling on it to phase out sulfuryl fluoride.
California has set a goal to reduce greenhouse gas emissions by 48% below 1990 levels by 2030. Phasing out sulfuryl fluoride would be equivalent to removing 1m automobiles from the road annually, the CBD estimated in the petition.
But the board rejected the request, claiming the agency “lacks sufficient information at this time to determine whether a sulfuryl fluoride phase-out is warranted given its use and overall impact on global temperature changes”.
It also said it did not currently have regulatory authority, nor did it plan to take the steps to give itself that authority.
The CBD disagrees with those claims, said Jonathan Evans, who developed the group’s petition.
“They have the ability to begin to tackle this highly potent greenhouse gas that is also toxic, but they didn’t just fail to phase it out, they also failed to track it,” he said.
In a statement to the Guardian, a Carb spokesperson said the agency was monitoring new information and “collaborating with the California Department of Pesticide Regulation”, the state agency that regulates the industry, to “determine any future action on sulfuryl fluoride, including availability of pest control alternatives”.
However, the pesticides agency had been unreliable because it receives funding from the sale of pesticides it regulates, which provides incentives to allow products such as sulfuryl fluoride to be sold, Evans said.
Banning the gas is also “not a slam-dunk” because there is no cost-effective alternative, Gaeta said. Though other states use pesticides that do not release greenhouse gases, the western drywood termite common in southern California cannot be killed with most other treatments, he added.
However, the pest control industry could trap and destroy the gas instead of releasing it post-treatment, which researchers say would significantly reduce emissions.
Evans said heating infested areas to 120F (49C) for roughly 30 minutes can eradicate the termites, and some localized treatments are effective. While some of these methods may be more expensive, they are “certainly less costly than climate change”, Evans said.
The CBD may approach the state’s legislature for action if regulatory agencies continue to ignore the problem, Evans added.
“It’s clear that sulfuryl fluoride is an incredibly dangerous pesticide, California is the country’s leading emitter, and it’s a highly potent greenhouse gas, and it’s alarming that California regulators aren’t addressing it,” he said.
