Large present-day and future climate forcing due to non-CO₂ emissions from global transport

Emissions from land-based transport, aviation, and shipping contribute significantly to climate change. Besides CO₂, these emissions include short-lived compounds that affect air quality but are also climatically relevant. We use a global chemistry-climate model to show that the climate effects of these non-CO₂ emissions are substantial across all transport sectors both now and in the future. In sum, the non-CO₂ impacts result in a cooling, which offsets the positive climate forcing from transport-induced CO₂ by around 80% at present and between 25 and 60% in different scenarios for 2050. The trade-off that air pollutants mitigate global warming is strongly reduced in a future scenario with low anthropogenic emissions, where even small remaining amounts of non-CO₂ compounds cause significant cooling as they are released in a very clean atmosphere. Our findings emphasize the need to take non-CO₂ effects into account when assessing climate protection strategies for the transport sectors.