Mitigation will improve air quality and 
human health in the near term notably because many air pollutants are 
148 In this context, ‘unabated fossil fuels’ refers to fossil fuels produced and used without interventions that substantially reduce the amount of GHG emitted throughout the life 
cycle; for example, capturing 90% or more CO2 from power plants, or 50 to 80% of fugitive methane emissions from energy supply. {WGIII SPM footnote 54}
co-emitted by GHG emitting sectors and because methane emissions 
leads to surface ozone formation (high conﬁdence). The beneﬁts from 
air quality improvement include prevention of air pollution-related 
premature deaths, chronic diseases and damages to ecosystems 
and crops. The economic beneﬁts for human health from air quality 
improvement arising from mitigation action can be of the same order 
of magnitude as mitigation costs, and potentially even larger (medium 
conﬁdence). As methane has a short lifetime but is a potent GHG, 
strong, rapid and sustained reductions in methane emissions can limit 
near-term warming and improve air quality by reducing global surface 
ozone (high conﬁdence). {WGI SPM D.1.7, WGI SPM D.2.2, WGI 6.7, 
WGI TS Box TS.7, WGI 6 Box 6.2, WGI Figure 6.3, WGI Figure 6.16, 
WGI Figure 6.17; WGII TS.D.8.3, WGII Cross-Chapter Box HEALTH, 
WGII 5 ES, WGII 7 ES; WGII 7.3.1.2; WGIII Figure SPM.8, WGIII SPM 
C.2.3, WGIII SPM C.4.2, WGIII TS.4.2}
Challenges from delayed adaptation and mitigation actions 
include the risk of cost escalation, lock-in of infrastructure, 
stranded assets, and reduced feasibility and effectiveness 
of adaptation and mitigation options (high conﬁdence). The 
continued installation of unabated fossil fuel148 infrastructure 
will ‘lock-in’ GHG emissions (high conﬁdence).