Modelling net-zero emissions energy systems requires a change in approach

Many countries and corporations are in the process of establishing net-zero GHG emission targets. One estimate suggests that such targets are in place or under discussion in countries representing over half of the world economy. This policy response to climate science, catalysed for many by the IPCC Special report in 2018 on Global Warming of 1.5°C, will require analytical support by the modelling community. Policy makers want to understand the pathways to get to net-zero, and the opportunities and costs of taking such radical steps to decarbonise their economies.

In a recent paper, my co-authors and I argue that energy system modelling approaches, widely used for supporting national climate and energy policy, were not ready to meet the net-zero challenge and needed to change.

The question is why would an energy model already used for supporting climate policy not be fit-for-purpose for analysing a net-zero emission energy system? In short, because a net-zero energy system is very different. All sectors have to aim for zero emissions, and where this is not possible (or prohibitively expensive), be ‘offset’ by options that essentially remove carbon dioxide from the atmosphere. The pace of action also needs to increase, because as the target level is reduced, the trajectory of necessary emission reductions steepen.

To address this challenge, we propose three areas where modelling can be improved; scope, function and practice. By scope, we refer to the additional options that models need to have in place to get to net-zero. Function refers to whether models can adequately represent net-zero systems that are different from the system of today, and provide insights to policy-relevant questions. Finally, practice concerns improved approaches to undertaking net-zero analyses, including representing deep uncertainty, and a broader range of stakeholder perspectives.

Focusing on scope, an earlier paper on modelling a UK net-zero energy system provides some useful insights. The first is that when modelling a system to achieve net-zero ambition, the CO2 sequestration and removal options are often deployed at scale, particularly if the analysis is driven by a least cost objective. The economics of such options look attractive under high carbon prices, particularly where their costs are discounted. However, such solutions are unlikely to be robust due to large uncertainties around their future deployment, with limited pricing in of these risks. A more nuanced consideration of their role is needed, balancing costs against a range of other factors, and avoiding ‘solution chasing’, where a model target has to be met by any means.

A useful avenue to counterbalance this supply-side focus is to explore how to achieve net-zero with a smaller energy system, based on actions to reduce energy demand. These include using less or alternative materials in industrial production, reducing mobility demand or using more efficient forms of transport, and improving the energy performance of buildings through energy efficiency retrofit. Such actions are often well-understood and can be delivered rapidly, necessary for the strong near term reductions required to hit a net-zero ambition. A recent study showed the potential for such measures, pushing back against the many integrated assessment model scenarios dominated by sequestration and removals.

Demand side measures are not without their own challenges but require better representation in models, and have the potential to reduce reliance on more speculative technologies that may not be ultimately deliverable in the long term.

Read the full paper.

Dr Steve Pye is an Associate Professor at UCL Energy Institute, University College London, whose research focuses on how to decarbonise the energy system using scenario modelling approaches.

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