Pressures: emissions

5.2.1 Electricity and fuel production

Figure 5.4: Global fuel shares of electricity generation in 20151
Notes: 1 Excludes electricity generation from pumped storage. 2 Includes geothermal, solar, wind, heat, etc. 3 Peat and oil shale are aggregated with coal. Source: IEA (2017).

The electricity and fuel production sector (labelled ‘energy’ in Figure 5.3) is the largest anthropogenic emitting sector of CO2, methane (CH4), SO2 and NMVOC, and the main emitting sector of other air pollutants. Within the sector, electricity generation contributed around 70 per cent of CO2, 71 per cent of SO2 and 72 per cent of NOX in 2014 (Hoesly et al. 2018).

Despite increases in renewable energy capacity, fossil fuels still dominate the global power system (see Figure 5.5). Threequarters of the sector’s SO2 emissions, 70 per cent of its NOX emissions and over 90 per cent of those of primary particulate matter less than 2.5 μm in diameter (PM2.5) are from coal-fired plants. Coal combustion is also the second most important anthropogenic source of global Hg emissions (International Energy Agency [IEA] 2016a). In 2015, gas-fired generation emitted close to 20 per cent of NOX from power generation, but barely any SO2 or primary PM2.5 (IEA 2016a).

From 1990 to 2015, global petroleum fuel production saw slow but sustained growth (see Figure 5.5). CH4 and NMVOC emissions from fuel production showed a corresponding increase (Figure 5.3). However, for electricity generation, production doubled between 1990 and 2015 (Figure 5.6), but emissions of air pollutants did not increase at the same rate. Most importantly, SO2 emissions from electricity generation declined after 2006 (see Figure 5.3).

The main reasons for this decoupling include:

  1. improvement of energy efficiency;
  2. tighter emission standards for power plants and progress of end-of-pipe control technologies;
  3. development of natural gas, renewable and nuclear power (Renewable Energy Policy Network for the 21st Century [REN21] 2016).
Figure 5.5: World petroleum refinery output by-product (million tons)
Source: IEA (2017).

However, despite existing policies and the announced aims, targets and intentions, electricity demand is expected to increase by two-thirds by 2040 (IEA 2016b). Both end-ofpipe pollution control technologies and coal with low sulphur content may be used to achieve lower air pollutant emissions.

Figure 5.6: World electricity generation by fuel (terawatt hours)1
Notes: 1 Excludes electricity generation from pumped storage. 2 Other = geothermal, solar, wind, tide, wave, ocean, biofuels, heat, etc. Source: IEA (2017).