Energy Systems
Rapid and deep reductions in GHG emissions require major 
energy system transitions (high conﬁdence). Adaptation options 
can help reduce climate-related risks to the energy system 
(very high conﬁdence). Net zero CO2 energy systems entail: a 
substantial reduction in overall fossil fuel use, minimal use of 
unabated fossil fuels153, and use of Carbon Capture and Storage in 
the remaining fossil fuel systems; electricity systems that emit no 
net CO2; widespread electrification; alternative energy carriers in 
applications less amenable to electrification; energy conservation 
and efficiency; and greater integration across the energy system 
(high confidence). Large contributions to emissions reductions can 
come from options costing less than USD 20 tCO2-eq–1, including 
solar and wind energy, energy efﬁciency improvements, and CH4 
(methane) emissions reductions (from coal mining, oil and gas, and 
waste) (medium confidence).154 Many of these response options are 
technically viable and are supported by the public (high confidence). 
Maintaining emission-intensive systems may, in some regions and 
sectors, be more expensive than transitioning to low emission 
systems (high confidence). {WGII SPM C.2.10; WGIII SPM C.4.1, 
WGIII SPM C.4.2, WGIII SPM C.12.1, WGIII SPM E.1.1, WGIII TS.5.1} 
Climate change and related extreme events will affect future energy 
systems, including hydropower production, bioenergy yields, thermal 
power plant efﬁciencies, and demands for heating and cooling (high 
153 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 50–80% of fugitive methane emissions from energy supply. {WGIII SPM footnote 54}
154 The mitigation potentials and mitigation costs of individual technologies in a speciﬁc context or region may differ greatly from the provided estimates (medium conﬁdence).