Indirect greenhouse gases contribute 15% of human-caused warming, study finds

Recent research highlights pollutants such as carbon monoxide and nitrogen oxides. missing from climate pledges, are blind spots that need addressing.

On 11 June 2026, a paper published in Science pointed out that a group of “indirect” greenhouse gases is responsible for about 15% of the warming humans have caused so far, or roughly 0.3 degrees Celsius, yet these pollutants remain largely absent from climate pledges and official emissions inventories.

The research has mentioned gases such as carbon monoxide, nitrogen oxides, non-methane volatile organic compounds, and hydrogen, which do not trap heat in the same direct way as carbon dioxide or methane. These gases can warm the planet indirectly by helping to form tropospheric ozone, extending methane’s lifetime in the atmosphere, and creating a small amount of carbon dioxide as they break down.

According to the study, these pollutants are not minor side issues but are major contributors to warming, ranking behind only carbon dioxide and methane in the human-caused climate system. Together with heat-absorbing black carbon, they account for a warming share that is larger than nitrous oxide and other better-known non-CO₂ gases. That makes them especially important for near-term climate action, because many of these emissions are short-lived, and their warming effects would ease relatively quickly if sources were cut.

Overlooked and under-addressed

Such reductions can also improve air quality, which means cleaner air and lower health risks could arrive alongside climate benefits, but a central criticism in the paper asserts that international climate rules still concentrate on the Kyoto-era basket of direct greenhouse gases, leaving indirect warming pollutants outside the main accounting system.

The paper’s authors say that this omission creates a blind spot in national climate plans, and makes it harder to measure the full climate impact of human activity. The concern is not that countries should ignore carbon dioxide cuts, but that they should expand the policy frame beyond carbon dioxide alone.

The analysis suggests that taking on these overlooked gases could deliver faster progress on controlling warming while also supporting public health goals.

The findings land at a time when climate researchers are increasingly warning that the warming problem is more complicated than a simple carbon ledger. Other recent studies have shown that changes in air pollution can alter how much sunlight Earth reflects, which is another reason emissions policy can have unexpected climate effects. In practical terms, the paper posits that governments should look beyond tailpipe and smokestack carbon emissions, the full mix of warming and air-quality pollutants that shape the atmosphere.