Example
Reducing fossil fuel combustion may improve local air quality alongside cutting emissions.
The catch
A possible co-benefit should not be presented as measured without evidence.
In more depth
Co-benefit, explained.
Co-benefits often decide whether climate policy wins support, because they arrive locally and quickly while the climate payoff is global and slower. Methane offers a clear case, since it helps form ground-level ozone. UNEP's Global Methane Assessment found that cutting methane would avoid premature deaths and crop losses as well as warming.
The IPCC also tracks the opposite, adverse side effects, such as energy crops competing with food production. In carbon markets, projects often advertise contributions to the Sustainable Development Goals. Those benefits can be real, yet they cannot repair a weak carbon credit, so judge the climate claim and the co-benefit on separate evidence.