CCS in Energy and Climate Scenarios

Publication Overview

The purpose of IAMs is to quantify the interactions and trade-offs between societal demands for energy, economic and environmental services, using a systems approach. These systems are typically the energy system, the economy, the earth-land system, the water system and atmospheric climate system, although every IAM does not necessarily include all these systems and have varying

Publication Summary

• Integrated assessment models (IAMs) are used to quantify the interactions and trade-offs between societal demands for energy, economic, and environmental services, using a systems-based approach.
• To stabilise global average temperatures, i.e. to end global warming, net CO₂ emissions released to the atmosphere must be reduced to zero. CO₂ emissions must be completely decoupled from economic growth.
• The purpose of this study is to provide a transparent approach to understanding results from IAMs and, in particular, the role of carbon capture and storage (CCS). It is not the intention of the study to advocate particular scenarios.
• CCS, with either fossil or bioenergy inputs, is a resilient climate mitigation technology.[1] It is deployed at sizeable scale in the vast majority of IAM scenarios that apply carbon budgets consistent with the Paris Agreement goal of limiting the global mean temperature increase to 2°C and pursuing efforts to stay below 1.5°C.
• Bioenergy carbon capture and storage (BECCS) is deployed after fossil CCS, compensating for residual fossil CO₂ emission through net negative CO₂ BECCS, a negative emissions technology (NET), is one of a number of technologies designed to achieve carbon dioxide removal (CDR) from the atmosphere. Without NETs, permanent reduction in global temperatures following an overshoot would not be achievable. However, the extent of future BECCS deployment is uncertain due to concerns over the availability of sustainable biomass resource.
• CCS capture costs of less than $100/tCO₂ in the power generation sector and less than $400/tCO₂ in industry are considerably lower than the whole system marginal abatement costs of CO₂ by mid-century calculated in IAMS. In IAMs, therefore, there are limiting and competing constraints on CCS deployment that are not solely related to its cost.
• 2°C scenarios have an upper limit on the cumulative CO₂ emissions allowable (carbon budget) in the range of 800-1 400 GtCO₂. The carbon budget for 1.5°C scenarios is in the range of 200-800 GtCO₂. According to the models studied, CCS is deployed less in scenarios with more ambitious climate goals. This is, to a large extent, a result of the residual carbon emissions from fossil fuels with CCS.
• Residual CO₂ emissions from fossil CCS with 90% capture rates and fixed capacity factors become incompatible with strict carbon budgets. Importantly, a recent IEAGHG study[2] has concluded that the 90% capture rate cap is actually an artificial limit. It is an historical benchmark, originally chosen for illustrative purposes.[3] There are no technical barriers to increasing capture rates beyond 90% in the three classic capture routes (post-, pre- and oxyfuel combustion) or with the broad suite of CO₂ capture technologies currently available or under development.
• As well as capture rate and capacity factor, another direct assumption that influences the role of CCS in IAMs is investment costs for technologies. Figure 1 highlights the wide range of CCS capture costs by fuel type and technology type across power generation.
• BECCS provides the majority of negative emissions in IAMs (with some CDR in the form of afforestation). It can provide additional space within the remaining carbon budget and may also compensate should global temperatures overshoot the target, but only as long as sufficient geological storage space remains under annual CO₂ injection rate limits.
• Actual CCS deployment to date is far removed from that depicted in the climate stabilisation pathways of most IAMs. There is a considerable gap between actual order books and the CCS deployment rates envisaged in most IAM scenarios to stabilise temperatures below 2°C.
• Only models that regularly update their base-year calibration, such as the IEA’s Energy Technology Perspectives (ETP) model, can keep track of clean energy technology progress[4] and, accordingly, with the gap between actual CCS deployment and the required CCS deployment in temperature stabilisation scenarios.

The diversity of mathematical approaches across the range of IAM typologies gives insights into the resilience of climate policy options across a range of scenarios and sensitivity analyses when combined across a range of models in a model inter-comparison project (MIP). Where the same technology deployments occur with the same scale and timing across the range of scenario analysis, this gives an indication of a resilient technology option across the range of input assumptions and uncertain future scenarios. Resilience is meant here in the sense that the technology option is consistently deployed across a range of uncertain scenarios, with a range of techno-economic specifications, giving an indication of a least-regrets investment option and is not overtly sensitive to an individual scenario.