A new study in the journal Science finds that indirect greenhouse gases such as carbon monoxide, nitrogen oxides, and molecular hydrogen account for about 15 percent of current global warming, roughly 0.3 degrees Celsius. These pollutants are mostly left out of international climate agreements like the Kyoto Protocol and Paris Agreement, even though they rank as the third-largest contributor to warming after carbon dioxide and methane. The sources include combustion, industrial processes, agriculture, and leaking hydrogen infrastructure. The researchers argue that existing air quality monitoring systems can be used to track these pollutants, since many are already regulated as harmful air pollutants. Addressing them would deliver both climate and public health benefits. The paper calls for updating global climate accounting frameworks to include these overlooked gases, especially as hydrogen use grows and could increase their warming impact if leaks are not controlled.
