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negative emissions (see Figure 22.5). There are various ways to reach these targets. While demand-side measures mostly reduce energy intensity, supply-side measures would increase the share of low-carbon options. These two indicators can provide an insight into the challenge that such reductions would pose.


The final energy-intensity (energy divided by GDP) reduction rate in many countries has typically been around 1-2 per cent


22


Figure 22.5: 2010-2050 energy intensity reduction rate and the 2050 share of low-greenhouse gas technologies in total energy mix of the scenarios included in the SSP database


70 60 50 40 30 20 10 0


0 0.5 1.0 1.5 2.0 2.5 3.0


Energy intensity reduction, 2010–2050 (% per year)


Historic reference Exceeds 3.5°C by 2100 Exceeds 2°C by 2100 Below 2°C in 2100


The colours of the dots indicate the projected 2100 temperatures. Source: Riahi et al. (2017); Rogelj et al. (2018).


per year in the period since 1970. This has been driven by both increase in energy efficiency and sectoral changes. Relatively high values for energy intensity reduction occurred during the 1973 and 2005 oil crises in response to prices and government policies in Organisation for Economic Co-operation and Development (OECD) countries that aimed to conserve energy (Schippers and Meyers 1992; Sweeney 2016). The share of low-greenhouse gas emitting technologies is at the moment around 20 per cent, consisting mostly of traditional biomass, hydropower and nuclear power. To reach the 2°C target, the combination of energy intensity reduction and increase in the share of low-greenhouse gas technologies would need to be significantly larger than historical values. As shown in Figure 22.5, the large-scale transformation required for this can be achieved by reducing energy demand (by means of energy efficiency and/or different and lower activity levels) and by decarbonizing energy supply (renewables, carbon-capture- and-storage, nuclear, fuel substitution). Energy efficiency increase, however, would need to be at least 2-3.5 per cent per year. Furthermore, the level of non-CO2


emitting supply


options would need to increase from around 15 per cent today to at least 40-60 per cent by 2050 (for the scenarios included


522 Outlooks and Pathways to a Healthy Planet with Healthy People 3.5


in Figure 22.5) or even 50 up to 100 per cent for the most stringent scenarios in the wider literature (van Vuuren et al. 2016; IPCC 2018). The low-range value of 40 per cent is only sufficient if combined with a rapid decline in energy demand. The amount of renewables would be around 30-40 per cent (Figure 22.5) or up to 60 per cent (full range) for 2 degrees (van Vuuren et al. 2016) and 70-85 per cent for 1.5 degrees C (IPCC 2018). It should be noted that the range for renewables largely overlaps with the range of total CO2


-free energy production,


as the different options can easily be substituted. All-in-all, the reduction in the carbon intensity of the global economy (rate of change of the ratio of CO2


over GDP) needs to increase from


around 1-2 per cent per year historically to around 4-6 per cent per year towards 2050; for the most stringent scenarios, values up to 8 per cent can be found in the literature (van Vuuren et al. 2016).


Emissions of greenhouse gases can be reduced by measures associated with energy demand and decarbonization of energy


supply. In addition, it is possible to reduce so-called non-CO2 emissions from both agricultural and energy systems. In other words, to achieve the Paris targets far-reaching transitions in energy, land, urban infrastructure (including transport and buildings), and industrial systems are needed (IPCC 2018). The contribution of these measures is discussed in more detail in the subsequent paragraphs. Box 22.2 discusses in more detail the role of land-based mitigation options.


Reducing energy demand Figure 22.6 presents the aggregated energy use of three different pathways consistent with the 2°C target. The total reduction in energy demand in the pathways is about 25 per cent, compared with the Trend scenario (see also Edelenbosch 2018). Studies focusing on the potential for energy efficiency show even higher possible efficiency improvement rates (Cullen, Allwood and Borgstein 2011; Graus, Blomen and Worrell 2011). Final energy demand is dominated by the industry, transport and residential sectors. Energy consumption in all three sectors would therefore need to be mitigated in order to reach sustainable development targets. Transport is a key sector, as here emissions are increasing most rapidly, driven by increasing emissions from car travel, road freight transport, marine transport and air travel. Different response options exist for decarbonizing the transport sector. For instance, one important option would be an almost complete electrification of most transport modes. This would require a corresponding transition in infrastructure, and its effectiveness in lowering emissions would depend on the carbon intensity of power generation. It should also be noted that, for many parts of the world, such a transition will take a lot of time and, in the meantime, it will be important to minimize emissions, for instance, by promoting car efficiency (Bae and Kim 2017). For modes that cannot be electrified, natural gas (in the short term), fossil fuel with carbon-capture-and-storage (CCS), hydrogen and bioenergy could play a role. Earlier, many studies identified bioenergy use as an effective response strategy for most transport modes. However, because of the possible negative impacts of bioenergy for other targets, the use of bioenergy is assumed to be limited here, restricting bioenergy to those sectors that are hard to abate or that could generate negative emissions. This means that effective measures for transport include electrification, rapid improvement of fuel efficiency and the development of new fuels (hydrogen, synthetic fuels). Alternatively, in a scenario focusing more


Share of low- to zero-emission technologies in 2050 (%)


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