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Report extract

Scenario trajectories and temperature outcomes

This World Energy Outlook provides a detailed stocktake of how far nations have come in their energy transitions, and a sobering picture of how far there still is to go. In the STEPS, global energy-related and industrial process CO2 emissions rebound quickly in 2021 and rise to 36 gigatonnes (Gt) in 2030. In the APS, emissions peak in the mid-2020s and return to just under 34 Gt in 2030, close to current levels. In the NZE, by contrast, emissions fall to 21 Gt in 2030, marking a decisive change of direction.

CO2 emissions in the WEO-2021 scenarios, 2000-2050

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The 2.6 Gt difference in emissions between the STEPS and the APS in 2030 highlights the “implementation gap” that exists between announced net zero pledges and the policy frameworks and specific measures that they require: pledges need to be underpinned by strong, credible policies and long-term plans to make them a reality. However, realising these pledges in full would fill less than 20% of the total gap between the STEPS and the NZE. This leaves a 12 Gt “ambition gap” between the APS and the NZE in 2030 that requires countries to go beyond existing pledges to be on course to achieve net zero emissions by 2050. In the NZE, methane emissions also reduce far more quickly than in the APS. If methane is also counted, then the ambition gap in 2030 would be around 14 Gt CO2-eq.1 If the world is off course in 2030, it will be extremely difficult to make up the lost ground later.

There are large differences in emissions trajectories in the APS: emissions decline by around one-third (or 3.5 Gt) in advanced economies by 2030, but rise by just over 10% (or 2.5 Gt) in emerging market and developing economies. The APS highlights the risk of a two-speed world emerging, in which a narrow focus on achieving national net zero pledges in some countries is coupled with limited efforts to prioritise emissions reductions in others, and little attention is given to technological spill-overs or to the scope for working in partnership. That could easily be a recipe for trade and other tensions to emerge, and it would militate against net zero emissions being achieved as cost-effectively as possible. Delivering the NZE is heavily dependent on all governments working together in an effective and mutually beneficial manner.

Global median surface temperature rise in the WEO-2021 scenarios, 2000-2010

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We have carried out new detailed analysis using the Model for the Assessment of Greenhouse Gas Induced Climate Change (“MAGICC”) to assess the impacts of these emissions trajectories on the average global surface temperature rise.2 In the STEPS, the global average surface temperature rise would exceed 1.5 degrees Celsius (°C) around 2030.3 Emissions in 2050 are around 32 Gt CO2: if emissions continue their trend after 2050, and if there are similar changes in non‐energy‐related greenhouse gas (GHG) emissions, the rise in temperature in 2100 would be around 2.6 °C. In the APS, the faster reduction in CO2 emissions to around 21 Gt in 2050 has little impact on the year in which 1.5 °C is exceeded, but the rise in temperature in 2100 would be restricted to around 2.1 °C. The temperature would continue to rise in both the STEPS and APS after 2100 because total CO2 emissions are still well above zero in 2100 in these scenarios.

In the NZE, CO2 emissions are net zero in 2050 globally and there are rapid reductions in all non-CO2 emissions (such as methane). The rise in temperature reaches a maximum level of just over 1.5 °C around 2050. The temperature then starts to decline slowly as a result of continued reductions in non-CO2 emissions, and by 2100 the rise in temperature has fallen to around 1.4 °C. In the SDS, CO2 emissions drop to zero around 2070 and there are rapid reductions in non‑CO2 emissions. The 1.5 °C level is exceeded in the early 2030s and the rise in temperature peaks at just under 1.7 °C around 2050.4 The SDS is in line with the Paris Agreement objective of “holding the increase in the global average temperature to well below 2 °C”, while the NZE goes further to be in line with the Paris Agreement objective of “pursuing efforts to limit the temperature increase to 1.5 °C”.

Temperature rise in the WEO 2021 scenarios (°C)

Scenario

2030

2050

2100

Confidence level:

50%

33% – 67%

50%

33% – 67%

50%

33% – 67%

Stated Policies

1.5

1.4 – 1.6

2.0

1.8 – 2.1

2.6

2.4 – 2.8

Announced Pledges

1.5

1.4 – 1.6

1.8

1.7 – 2.0

2.1

1.9 – 2.3

Sustainable Development

1.5

1.4 – 1.6

1.7

1.5 – 1.8

1.6

1.4 – 1.7

Net Zero Emissions by 2050

1.5

1.4 – 1.5

1.5

1.4 – 1.7

1.4

1.3 – 1.5

Note: Shows the maximum temperature rises with 33%, 50% and 67% confidence levels. Source: IEA analysis based on outputs of MAGICC 7.5.3.

The difference in temperature rise between the scenarios has stark consequences for global ecosystems and human well-being. The higher the temperature rise, the greater the risks of severe weather events such as extreme heat, drought, river and coastal flooding and crop failures. Even during the last decade, with an average temperature rise of 1.1 °C above pre-industrial levels, extreme heat events occurred almost three-times more frequently than in pre-industrial times. In the STEPS, around 2050, there would be a 100% increase in the frequency of extreme heat events compared to today and these would be around 120% more intense; there would also be a 40% increase in ecological droughts that would be around 100% more intense. In the NZE, the increase in frequency of extreme heat events would be lower at around 45% and ecological droughts would be less than 20% more frequent.

By 2100, as the temperature trajectories of the scenarios diverge, differences in the frequency and intensity of extreme weather events would become even more stark. There is around a 10% chance that the rise in temperature in the STEPS would exceed 3.5 °C in 2100. This would lead to an 80-130% increase in the frequency of ecological droughts and a two-to-threefold increase in their intensity. Extreme rainfall would happen up to twice as often as today and be three-to-four-times more intense. The risk of ice sheet collapse and disruptions to ocean circulation currents would also be substantially higher.5 This in turn could precipitate irreversible changes in the permafrost, boreal forests and the Amazon rain forest, potentially accelerating warming.

Peak temperature rises in the WEO-2021 scenarios

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References
  1. One tonne of methane is considered to be equivalent to 30 tonnes of CO2 based on the 100-year global warming potential (IPCC, 2021).

  2. MAGICC climate models have been used extensively in assessment reports written by the Intergovernmental Panel on Climate Change. MAGICC 7, the version used in this analysis, is one of the models used for scenario classification in the IPCC’s 6th Assessment Report (IPCC, 2021). Emissions of all energy-related GHG from the WEO-2021 scenarios are supplemented with commensurate changes in non-energy-related emissions based on the scenario database published as part of the IPCC Special Report on Global Warming of 1.5 °C (IPCC, 2018). All changes in temperatures are relative to 1850-1900 and match the IPCC 6th Assessment Report definition of warming of 0.85 °C between 1995-2014.

  3. Unless otherwise stated, temperature rise estimates quoted in this section refer to the median temperature rise, meaning that there is a 50% probability of remaining below a given temperature rise.

  4. All scenarios in the WEO-2021 have a similar temperature rise over the 2021-2030 period and a similar year in which 1.5 °C warming is exceeded. This results from a balance between reductions in emissions of gases that have a large near-term warming effect on the climate (such as methane) and reductions in aerosols and gases that have a large near-term cooling effect on the climate (such as sulphur dioxide). 

  5. The uncertainty ranges associated with temperature rises shown in do not take into account the possibility of these low likelihood, high impact events, which could generate feedbacks and cause additional atmospheric warming.