Can CO₂ Capture and Storage Unlock ‘Unburnable Carbon’?

Publication Overview

This study has undertaken an initial assessment on the relevance of CCS in terms of the unburnable carbon issues. This consisted of the following tasks:

1. Undertake a comprehensive literature review to identify and assess those studies done to date which are relevant to, include or comment upon the role of CCS in the issues of unburnable carbon.
2. Assess the assumptions, methodologies, any contentious subjects, and understand differences in these studies.
3. Identify and assess sources of information on the global potential for CCS deployment, including storage potential.
4. Potential issues that would contribute to better understanding and assessment of this topic (which are of a technical nature and thus IEAGHG could address), will be identified and recommendations made for further work, including whether any work is necessary relating to global storage capacity and CCS global potential.

Publication Summary

• The global ‘carbon budget’ in emission scenarios for climate change mitigation implies that a certain amount of fossil fuel reserves should not be used and their resulting greenhouse gases emitted to atmosphere. This concept is often referred to as ‘unburnable carbon’.
• As carbon capture and storage (CCS) is a technology that prevents or reduces the emissions of CO₂ to the atmosphere, it has the potential to enable use of fossil fuels in carbon-constrained scenarios.
• In order to evaluate the potentially unburnable carbon of fossil fuel reserves, it is necessary to estimate the overall remaining fossil fuel reserves and compare them with the global carbon budget.
• Integrated assessment models (IAMs) are a good means to evaluate carbon budgets as they have a large coverage of technologies, geographical scope, economics and climate data. These models are widely used in publications of the Intergovernmental Panel on Climate Change (IPCC), the International Energy Agency (IEA) and academia, and most of them cannot achieve a 2°C or lower scenario without CCS. This report selects and investigates a subset of models that focus on technology options and include CCS.
• This study does not aim to assess or provide evidence of the ‘unburnable carbon’ concept but rather to look at the role of CCS technologies in this regard. It will assess the assumptions, methodologies, any contentious subjects and differences related to this topic.
• This study found that the impact of CCS on unburnable carbon appears to be material up to 2050 and further increases up to 2100. This applies especially to coal but also to gas to some extent.
• Model assumptions and cost data availability do generally not limit uptake of CCS in IAMs. However, other reasons seem to limit CCS uptake in models, and the authors of this report hypothesise it could be that residual emissions from CCS, for which CO₂ capture rates of 85-90% are usually assumed, are the reason. It is recommended to investigate this further and to give consideration in R,D&D to increasing capture rates.
• Uncertainties in IAMs and fossil reserve estimates can influence the total amount of carbon considered as unburnable.
• The authors review estimates of global CO₂ geological storage capacity, and find that estimates obtained from volumetric approaches are large and well above the extent of the CO₂ emissions related to fossil fuel reserves.
• Storage capacity estimates from dynamic approaches are likely to be lower, and hence further work on improving dynamic storage efficiency, such as pressure management by brine extraction, is required.
• The related additional costs for pressure and brine management should be considered in IAMs.