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Carbon emissions

Carbon emissions increase further in the ET scenario with the power sector the main source of emissions

In the ET scenario, CO2 emissions from energy use continue to edge up through much of the Outlook, increasing by around 7% by 2040.

CO2 emissions in ET scenario
CO2 emissions in ET scenario
CO2 emissions by sector
CO2 emissions by sector

The upward pressure on carbon emissions from continuing population growth and, most importantly, increasing prosperity in the developing world is largely offset by quickening gains in energy intensity and to a lesser extent by changes in the fuel mix reducing the level of carbon intensity.


Although the rate of growth in carbon emissions is much slower than in the past 20 years, emissions are still growing more quickly than the sharp decline likely to be necessary to be consistent with achieving the Paris climate goals (see the alternative ‘Rapid transition’ scenario below).


Despite the carbon intensity of the global power sector falling by around a third over the Outlook, the rapid growth in electricity consumption means that the power sector is the largest source of increase in CO2 emissions over the same period, with its share in the global energy system increasing to around 40% by 2040. This is higher than industry or transport which each account for around a quarter of CO2 from energy use, with buildings contributing the remainder (10%).

Alternative scenario – rapid transition

A more rapid transition to a lower carbon energy system

CO2 emissions
CO2 emissions
* See data sources for scenarios included
CO2 in 2040: ET vs RT scenario
CO2 in 2040: ET vs RT scenario

The alternative ‘Rapid transition’ (RT) scenario combines all the policy measures in the lower-carbon scenarios for industry and buildings; transport and the power sector in one single scenario.


In the RT scenario, CO2 emissions fall by around 45% by 2040 relative to current levels. The scale of this reduction is broadly in the middle of a range of external projections which claim to be consistent with meeting the Paris climate goals, and is broadly similar to the reduction in carbon emissions in the IEA’s Sustainable Development Scenario.


The power sector accounts for most of the CO2 emissions savings


Around two-thirds of the reductions in CO2 relative to the ET scenario stem from the substantial decarbonization of the power sector. The power sector is the single largest source of CO2 emissions from energy use, and the extensive fuel-on-fuel competition means policy interventions can have significant impacts on the fuel mix.


The reduction in CO2 from industry and buildings accounts for much of the remaining reduction in emissions, reflecting improved efficiency, greater use of CCUS and switching into lower-carbon fuels.


Despite the large number of policy measures and initiatives applied in the transport sector, the reduction in CO2 is relatively small.

The reduction in emissions in the Rapid transition scenario stems from greater efficiency, fuel switching and use of CCUS

The fall in carbon emissions in the RT scenario relative to 2017 levels reflects a combination of: gains in energy efficiency; a switch to lower-carbon fuels; and greater use of CCUS.

CO2 emissions in RT scenario, 2017-2040
CO2 emissions in RT scenario, 2017-2040
* See data sources for scenarios included
Primary energy consumption by fuel
Primary energy consumption by fuel

The gains in energy efficiency means energy demand increases by around 20% in the RT scenario by 2040, compared with a third in the ET scenario.


The shift to lower carbon fuels reflects a combination of rapid growth in renewable energy – which more than accounts for the entire increase in primary energy – and a sharp contraction in the use of coal. By 2040, renewables account for around 30% of primary energy.


Oil and gas provide nearly half of global energy in 2040 in the RT scenario


Despite the strong growth in renewables, oil and gas account for close to 50% of primary energy in 2040 in the RT scenario. The level of oil consumption falls to around 80 Mb/d in 2040, with roughly 60% of this remaining use in transport and much of the rest in the non-combusted sector. In contrast, gas continues to grow aided by growing use of CCUS – with close to a third of natural gas in the RT scenario in 2040 being used in conjunction with CCUS.


CCUS is used in both power and industry and captures almost 4.5 Gt of CO2 emissions by 2040 in the RT scenario.