A closer look at the modelling behind our global Roadmap to Net Zero Emissions by 2050

The IEA has been examining the critical topic of net zero emissions by 2050 from different perspectives over the last two years. In the World Energy Outlook (WEO) 2019, we provided an initial assessment of the broad scale of the challenge. Last summer, we assessed the level of accelerated technology innovation needed for the world to reach net zero emissions by 2050 in our revamped Energy Technology Perspectives (ETP) series. And in WEO 2020 in October, we laid out the major steps that need to be taken through 2030, including in terms of changes in consumer behaviour.

And next week, we are publishing our deepest dive yet with the release our new special report, Net Zero by 2050: a Roadmap for the Global Energy Sector, on 18 May.

The report will present a pathway called the Net Zero Emissions by 2050 (NZE) Scenario to reach this goal globally, which would be compatible with a 50% probability of limiting the average global temperature rise to 1.5 °C.

The NZE Scenario builds on our best understanding of the availability and prospects of technologies, potential for behavioural changes, as well as a fair and balanced approach towards each country’s own circumstances. This is a particularly important issue with regard to many developing economies, which are called upon to help address climate change despite having contributed only minimally to the accumulated greenhouse gas emissions that are causing it. It also takes into detailed account the physical energy infrastructure that is in place today, including for different types of fuel supply, power generation and end-uses such as industry, transport and buildings.

There are a number of pathways that could lead to net zero in 2050, depending on the pace of innovation in new and emerging technologies; the extent to which citizens are able or willing to alter their behaviour; the availability of sustainable bioenergy; and the extent and effectiveness of international collaboration; and other significant variables. While our Roadmap will describe one such pathway in detail, it will also address key uncertainties and discuss other pathways.

The NZE Scenario rests on three key principles:

• The uptake of all technologies and emissions reduction options is dictated by costs, technology maturity, policy preferences and potential trade-offs with broader societal goals, and market and country conditions.
• All countries cooperate towards achieving net zero emissions worldwide. This involves all countries participating in efforts to meet the net zero goal, working together in an effective and mutually beneficial way, and recognising the different stages of economic development of countries and regions, and the importance of ensuring a just transition.
• An orderly transition across the energy sector. This includes ensuring the security of fuel and electricity supplies at all times, minimising stranded assets where it makes economic sense and aiming to avoid volatility in energy markets.

Inevitably, the design of the NZE Scenario means we had to make choices. For example, we chose to consider all technologies that are available to the market today or are currently under development. Of course, not all technologies will be deployed in every country. But the NZE Scenario takes into account each country’s particular circumstances. Having a broad technology basket helps the NZE Scenario respond to the formidable task of transforming the entire energy sector within just 30 years in a cost-effective manner, even as the world economy more than doubles in size and the global population increases by 2 billion people.

Such choices, of course, affect the energy trends in the NZE Scenario. An examination of comparable scenarios of the Special Report on 1.5°C by the Intergovernmental Panel on Climate Change is instructive. The IPCC special report includes 90 individual scenarios that have at least a 50% chance of limiting warming in 2100 to 1.5 °C.1 Only 18 of these scenarios have net zero CO₂ energy sector and industrial process emissions in 2050 – the objective of the NZE Scenario. In other words, only one-fifth of the 1.5 °C scenarios assessed by the IPCC have the same level of ambition for reductions in energy and industrial process emissions as our NZE Scenario. For example, in the “low-energy demand scenario” – which is used as the most ambitious “illustrative model pathway” in the IPCC special report’s Summary for Policymakers – energy sector and industrial process emissions in 2050 are 4.5 billion tonnes of CO₂ (Gt CO₂) higher than in our NZE Scenario. In addition, the NZE Scenario achieves universal energy access by 2030 – a goal that is not included systematically in IPCC scenarios.

Comparing the energy sector transformations in the 18 IPCC scenarios and the one in the NZE Scenario reveals the following:

• Use of carbon capture, utilisation and storage (CCUS): The scenarios assessed by the IPCC have a median of around 15 Gt CO₂ captured using CCUS in 2050, double the level in the NZE Scenario.
• Use of carbon dioxide removal technologies: CO₂ emissions captured and stored from bioenergy with CCUS (BECCS) and direct air capture in the IPCC scenarios range from 3.5 Gt CO₂ to 16 Gt CO₂ in 2050, compared with 1.9 Gt CO₂ in the NZE Scenario.
• Bioenergy: The IPCC scenarios have a median of 200 exajoules (EJ) of primary bioenergy in 2050 (compared with 65 EJ today) and a number of them have more than 300 EJ. The NZE Scenario has 100 EJ of primary bioenergy in 2050. In the NZE Scenario, there is no overall increase in cropland use for bioenergy production and no bioenergy crops are developed on forested land.  
• Energy efficiency: Total final consumption in the IPCC scenarios ranges from 300 EJ to 550 EJ in 2050 (compared with around 410 EJ in 2020). The NZE Scenario has final energy consumption of 340 EJ in 2050.
• Hydrogen: The IPCC scenarios have a median of 18 EJ of hydrogen in total final consumption in 2050. In the NZE Scenario, 33 EJ of hydrogen is used in final consumption in 2050.2
• Electricity generation: The shares of wind and solar in total electricity generation in 2050 in the IPCC scenarios range from around 15% to 80%, with a median value of 50%. In the NZE Scenario, wind and solar provide 70% of total generation in 2050.
• Use of fossil fuels: The IPCC scenarios have a median of 155 EJ of fossil fuels in 2050, compared with the NZE Scenario’s 120 EJ. 

Our Roadmap will describe the global steps needed to achieve the NZE Scenario as well as their implications. In particular, it will include concrete milestones for technology deployment, sectoral trends and the choices that have to be made at different points in time to decarbonise each sector.

These milestones will require a massive scaling up of ambition coupled with unwavering government attention, in particular in the next 10 years. This short-term focus is driven partly by the opportunity afforded by the unprecedented momentum we are currently seeing behind efforts to address climate change. But deep transformations are also required by 2030 because of the extreme tightness of the remaining global emissions budget and the risk of locking-in high emissions infrastructure. In practice, some of these milestones will be met, others will not, and some technologies will fail to deliver and others will surprise us – technology deployment rarely ever follows an idealised trajectory.

Our new NZE Scenario should not be mistaken as the path to net zero emissions by 2050. Rather, it is a path that seeks to provide clarity on what delivering on ambitions to reach net zero by 2050 might actually mean in practice. Beyond the main scenario itself, our report therefore will explore the implications of an accelerated energy sector transformation for the economy, industry, citizens and governments. Many of these implications will remain relevant in any path to net zero emissions by 2050. And our report will lay out the priority actions that governments will need to take in order to live up to the challenge.

IEA Executive Director Fatih Birol kicked off this ambitious project in September 2020 with the goal of bringing about the best possible modelling assessment, drawing on expertise and tools from across the IEA. Results from both the WEO and ETP models have been combined with those from the International Institute for Applied Systems Analysis (IIASA) – in particular the Greenhouse Gas - Air Pollution Interactions and Synergies (GAINS) model – to evaluate air pollutant emissions and resultant health impacts. And, for the first time, our results were combined with the IIASA’s Global Biosphere Management Model (GLOBIOM) to provide data on land use and net emissions impacts of bioenergy demand.

The WEO and ETP models have also been linked to the Global Integrated Monetary and Fiscal (GIMF) model of the International Monetary Fund (IMF) to assess the impacts of changes in investment and spending on global GDP. Finally, the analysis was informed by discussions with modelling teams from across the world, including from China, the United States, Japan, the European Union and the IPCC.

Such a major project brings with it significant expectations from governments and non-governmental organisations, companies, academia and beyond. Notably, the report was requested by the UK government’s Presidency of COP26 as an input to the climate negotiations in Glasgow in November. We do not take such expectations lightly; this explains our detailed modelling efforts as well as our extensive external consultations. We are particularly grateful for the invaluable insights provided by the nearly 100 experts from government, industry, IPCC, academia and NGOs who took part in the peer review process for the report.

It is now our hope that our report will inform and stimulate the debate on how our collective climate goals can be achieved in practice, regardless of different opinions and backgrounds.