3.1 4.c - Reducing emissions and evaluating mitigation

Energy efficiency and conservation

Energy efficiency means obtaining the same useful service with less energy input. Better insulation reduces the heat a building loses, so less heating is needed to maintain the same indoor temperature. An efficient motor converts a larger proportion of supplied energy into useful movement. These changes reduce emissions when the energy saved would otherwise have been supplied by an emitting source.

Energy conservation reduces the demand for energy services themselves, for example by travelling less, heating fewer rooms or avoiding unnecessary lighting. Efficiency and conservation can work together, but they are distinct: changing a lamp to provide the same light with less electricity is efficiency; turning off an unnecessary lamp is conservation. Reducing waste can improve living standards, whereas reducing essential heating in an already cold home can harm health. Policy must distinguish unnecessary demand from unmet need.

An illustrative heating improvement cuts the energy needed for a fixed indoor temperature from 100 to 70 units. If fuel and use remain the same, the direct reduction is 30 units. But lower bills may encourage occupants to heat more rooms, reducing the saving. This rebound effect means technical potential and measured outcomes differ. It does not imply efficiency never works: the size of rebound must be assessed.

Upfront cost, landlords' incentives, installation skills and consumer information can limit adoption. A landlord may pay for insulation while a tenant receives the energy saving; a low-income household may lack capital despite a favourable long-term return. Grants, standards and finance can address different barriers. Efficiency also avoids some new energy infrastructure, but savings must be measured across the system rather than inferred from appliance labels alone. IPCC AR6 Working Group III Chapter 5 assesses demand and service provision, 2022.

Fuel shifts and low-carbon energy

A fuel shift changes the energy source supplying a service. Replacing coal-fired generation with gas can reduce carbon dioxide per unit of electricity because combustion chemistry and generating efficiency differ. However, gas still releases carbon dioxide, and methane leakage during extraction and transport can reduce the climate benefit. A lower-emissions fossil fuel is not the same as a zero-emissions system.

Wind, solar, hydroelectric and nuclear generation can supply electricity with low lifecycle greenhouse-gas emissions. Lifecycle assessment includes construction, fuel supply, operation and disposal. Wind and sunlight do not require fuel combustion during generation, but turbines, panels, networks and storage still require materials and energy. “Low carbon” is therefore more accurate than assuming every component has no emissions. IPCC AR6 Working Group III Chapter 6 assesses energy-system transitions, 2022.

Electrification can transfer the benefit to transport and heating. An electric vehicle or heat pump depends partly on how its electricity is generated, the efficiency of the device and its manufacture. Cleaner generation and efficient end use reinforce one another. The reverse is also true: rapidly increasing electricity demand can make decarbonisation harder if it requires continued fossil generation.

Different resources create geographical trade-offs. Wind and solar vary with weather and time, requiring flexible demand, storage, interconnection or other supply. Hydropower depends on water availability and can alter river ecosystems and settlements. Nuclear power needs large investment, waste management and public confidence. Siting, transmission lines, skills and access to finance can constrain all technologies. A reliable transition usually needs a coordinated system, not one favoured device considered alone.

Distribution matters as well as technical performance. A new clean-energy industry can create employment while an existing mining area loses work. Retraining, investment and affordable access help make change politically durable. A strategy that reduces national emissions but leaves essential energy unaffordable may face resistance and deepen inequality.

Carbon capture and forestry

Carbon capture and storage separates carbon dioxide from a source, transports it and stores it in a reservoir intended to retain it over long periods. At an industrial facility, capture can reduce emissions that would otherwise enter the atmosphere. Geological storage uses suitable porous rock beneath an effective seal, with site assessment and monitoring to manage leakage risks. Capture, transport and storage must all function for the claimed benefit to be delivered.

Capture uses energy and is rarely complete. A complete comparison includes both the residual process emissions and the additional emissions from operating the capture system.

Worked example — capture versus avoided emissions

Illustrative dataset: a baseline process releases 100 emission units. Capture retains 90, while additional energy and supply-chain activity add 15.