Climate consistency of IEA’s Sustainable Development Scenario

This post presents the results of checking the climate consistency of the most ambitious energy transition scenario from the International Energy Agency (IEA).

Energy transition scenarios are meant to inform policy-makers and society about the implications of potential roadmaps for the energy sector. In the context of addressing the climate change challenge, the goal of scenarios should be achieving a targeted level of global warming. Hence, the climate consistency of scenarios should be clearly and transparently reported, but often this is not the case. Moreover, it is common to find ambiguity in climate consistency reporting, with scenarios claiming to adhere to current policy commitments (e.g., Paris Agreement) without properly backing these statements.

Policy agreements themselves often embody a significant ambiguity. It is for instance not clear what does it take to be consistent with the Paris Agreement, so different interpretations are used. Unfortunately, how IPCC has reported available carbon budgets has also contributed to the overall ambiguity, since different numeric values of carbon budgets can be inferred from its publications. Moreover, the fact that global warming is linked to total emissions and not only to energy-related emissions is often by-passed by implicit or explicit assumptions about the evolution of non-energy emissions, for which the proposed energy transition scenarios do not provide any means for mitigation. And on top of all of this we have the significant uncertainty attached to carbon budgets themselves.

The lack of clarity in reporting the climate consistency of energy transition scenarios strongly undermines its value, since chances to trigger the wrong policy or societal response are high.

Carbon budgets (CBs) are an appropriate yardstick to check the climate consistency of transition scenarios. The IPCC compiles the available scientific knowledge on climate change, including carbon budgets. The IPCC periodically produces Assessment Reports (AR) where the available knowledge on climate change is compiled. The fifth AR was released in 2014, and the sixth AR is due for 2021-2022. Climate and earth system models are updated for each AR, and therefore changes in carbon budgets are to be expected. Since climate and earth system models incorporate ever increasing detail about physical mechanisms (including feedbacks), carbon budgets estimates can be expected to reduce in updated ARs.

In 2018 the IPCC released its last publication updating carbon budgets (Special Report on 1.5C – SR1.5C). This publication is still based on model results from the AR5, but introduced several methodological changes to derive carbon budgets, lading to a significant increase of CBs over those presented in AR5. In here  and here we discuss this update in CBs and its implications. One of the effects of this update in CBs is that some of the principal energy transition scenarios that before the SR1.5C were reported to be consistent with a 2C global warming, suddenly were reported to be consistent with 1.5C global warming (without reducing its cumulative emissions).

Comparing the cumulative CO₂ emissions from transition scenarios with the available carbon budgets provides a direct check of its climate consistency.

Energy transition scenarios provide high detail for energy-related CO₂ emissions, and the proposed means to mitigate them. However, CBs make reference to total CO₂ emissions. Therefore, for checking climate consistency total cumulative CO₂ emissions are the metric to be compared with available carbon budgets. This means that energy-related CO₂ emissions need to be complemented with industrial process CO₂ emissions and LUCUCF (land use, land use change and forestry) CO₂ emissions before comparing with the available carbon budgets.

Most energy transition scenarios do not address the details of mitigation in industry-process and LULUCF emissions, but still they make statements about climate consistency. For this purpose, they rely on unclear, non-transparent and unbacked assumptions about mitigation of non-energy related emissions. Often, the implicit mitigation for non-energy related emissions turns out to be far more ambitious than that for energy-related emissions, which is in stark contrast with the absolute lack of mitigation measures that these scenarios propose for non-energy related emissions.

In order to avoid this inconsistency, and in the absence of detailed transition analysis for non-energy related emissions, we propose that the climate consistency of the energy scenario is analyzed by framing it with the range of likely non-energy related emissions consistent with the proposed energy transition scenario. This range of non-energy related cumulative CO₂ emissions can be defined by the two following cases:

•         Business As Usual (BAU) CO₂ emissions from industry-process and LULUCF, consistent with historic values and trends.
•       Mitigation in non-energy related CO₂ emissions that has the same ambition as that deployed in the energy transition scenario for energy-related CO₂ emissions, where ambition is defined by the time-dependent ratio of transition to BAU emissions.

Among the most influential energy transition scenarios during the last decades are those developed by the International Energy Agency (IEA) and reported in its annual World Energy Outlook (WEO). 

The 2019 WEO includes 3 scenarios: Current Policies Scenario (CPS), Stated Policies Scenario (SPS) and Sustainable Development Scenario (SDS). The SDS is by far the more ambitious of the three in climate terms: Cumulative energy-related emissions between 2020 and 2100 from SPS and CPS are about 360% and 500% those of SDS, with SPS and CPS still emitting additional CO₂ after 2100. Here we will address the climate consistency of the SDS scenario (the one with the highest climate ambition).

In the WEO 2019, IEA claims the SDS to be consistent with 1.8C global warming with 66% likelihood, or 1.65C global warming with 50% likelihood. It is worth noting that the reduction of CO₂ energy-related emissions of the SDS from the SPS already includes 9% of Carbon Capture Use and Storage (CCUS). As we will see below, the analysis of the climate consistency of the SDS rather points (at best) to an alignment with a 2C global warming with 50% likelihood (see Fig.1).

As discussed above, the analysis of climate consistency requires evaluating the total cumulative CO₂ emissions and comparing them with the available carbon budgets. The energy-related emissions associated to the SDS are taken from the WEO 2019. Two estimates of industry process CO₂ emissions and LULUCF CO₂ emissions will be used to frame the likely evolution of this sectors in parallel to the implementation of the SDS energy transition roadmap: BAU and similar ambition to the mitigation in the energy-related emissions.

For industry process emissions, starting from the current values, the BAU follows the historic increasing trend with a linear evolution. The other extreme for industry process emissions assumes the same time evolution of mitigation as in energy-related emissions, leading to zero emissions a bit before 2070.

For LULUCF, starting from the average level of emissions from the last couple of decades, the BAU implements the historic increasing trend using a linear evolution up to 2040, when LULUCF are assumed to stabilize and keep constant up to 2100. The other extreme for LULUCF emissions assumes the same time evolution of mitigation as in energy-related emissions, leading to zero emissions a bit before 2070.

Figure-1 presents the results. Carbon budgets as of 2020 for different levels of global warming and likelihoods are presented at the right (yellow bars) and include the uncertainty range recommended by IIPC in the 2018 1.5C Special Report. Cumulative emissions (2020-2100) for the SDS transition scenario are presented at the left for the two cases of industry process emissions and LULUCF emissions: Energy-related emissions from SDS are presented in blue bars (the same for both cases); The bar at the left includes the BAU process industry and LULUCF cumulative emissions, while the bar at the right has industry process and LULUCF emissions with the same mitigation ambition as the energy-related emissions.

As it may be seen, total cumulative emissions are well above the available carbon budgets for 1.5C (67% and 50% likelihoods). The case that considers a similar mitigation ambition for industry process and LULUCF emissions as that for energy-related emissions has total cumulative emissions that fall within the upper uncertainty range of the carbon budget for 2C at 67% likelihood, and close to the median value of the carbon budget for 2C at 50% likelihood. However, if BAU emissions are considered for industry process and LULUCF (which seems more consistent with a transition scenario that does not foresee any measure to mitigate these emissions), the cumulative emissions are almost in the limit of the upper uncertainty range of the 2C at 50% carbon budget, and hence would be likely to lead to a global warming above 2C.

Figure-1: Cumulative emissions of IEA’s SDS (2020-2100) compared with available carbon budgets. Energy-related emissions are those from the SDS. For process and LULUCF emissions two cases are presented: BAU and same ambition as for energy-related emissions.

The analysis herewith presented has focused on the SDS from IEA, concluding that this energy transition scenario, at best would be aligned with 2C global warming, but that it significantly overshoots the 1.5C climate goal. However, this conclusion can be extended to other of the available main energy transition scenarios which also belong to the 800 – 900 GtCO₂ cumulative energy-related emissions climate tier.

Historic GHG emissions have already produced 1.1C of global warming, and its impacts are being felt around the world with increasing intensity year after year. Avoiding climate impacts that can seriously challenge the integrity of our socioeconomic and environmental systems would require limiting global warming to 1.5C, and reaching this goal requires the whole world completing the transition before 2050. Even if we fail to stabilize global warming to 1.5C, the faster we can transition the better for our socio-economic systems. In this context, and taking into account how these influential energy transition scenarios lock-in policies and investments for the following decades, it is difficult to understand why we have not been analyzing more ambitious scenarios since several years ago, so that policy-making can be properly informed.

In the post-COVID period, the opportunity window to address structural change should be used to increase transition rates and bring us into more climate-ambitious transition roadmaps.