A study published in Science reveals that overlooked pollutants account for approximately 15% of current global warming from human emissions, equivalent to about 0.3°C. These so-called "indirect greenhouse gases" include carbon monoxide, non-methane volatile organic compounds, nitrogen oxides, and molecular hydrogen. Most of these substances fall outside existing climate policy frameworks, the paper's authors argue.
The findings highlight a critical blind spot in international climate agreements. While carbon dioxide and methane dominate regulatory attention, these indirect gases contribute significantly to warming through complex chemical reactions in the atmosphere. Experts warn that ignoring them undermines efforts to meet Paris Agreement temperature targets.
Data from the study indicates these pollutants are not directly regulated under most national or global climate policies. The researchers compiled emissions data and atmospheric modeling to quantify their warming impact. The 0.3°C figure represents a non-trivial fraction of the roughly 1.2°C of total human-caused warming observed since pre-industrial times.
Without policy intervention, emissions of these indirect greenhouse gases could rise further, particularly from industrial processes and transportation. The study's authors call for expanding regulatory frameworks to include these substances. Some nations have begun monitoring them, but comprehensive action remains limited.
A counter_argument notes that measuring and attributing warming from these indirect gases is more uncertain than for direct GHGs, making regulation technically and politically challenging. Critics caution against diverting focus from the primary driver—carbon dioxide.