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The Paris Agreement has ambitious goals of achieving net-zero emissions by the second half of the century, and remaining well-below 2^oC, and pursuing reductions towards 1.5^oC, by the end of the century. The Agreement was rightly lauded as a huge achievement with emissions reduction commitments from almost every world nation for the first time. A fantastic start, albeit after about fifteen years of inaction.

Emission reduction: short on ambition, over-reliant on future tech breakthroughs

However, several important issues persist with the achievement of these goals.

1. The current country commitments fall short of achieving either of them and therefore will require an increase of ambition over the next 10 years.
2. The difference in the level of effort between these temperature goals is actually quite striking. While 0.5^oC may not sound like much, it is in reality a huge difference in ambition.
3. Many studies show that to achieve these goals there is a reliance on technologies which do not exist yet, many of which will be used to achieve net-zero or even net-negative emissions.

Our analysis therefore aims to understand the implications of these issues together. It considers:

• The difference between “well-below 2^oC” vs. “towards 1.5^oC”.
• The difference between  increased ratcheting from 2020 and delaying action until 2030.
• How much NETS ((Negative Emissions Technologies) such as Biomass with Carbon Capture and Storage (BECCS) are needed for each scenario.

We use the TIAM-UCL model with elastic demand in order to consider changes in the energy system for the remainder of the century.

The verdict: 40-50 years to reach negative emissions in all scenarios

The findings of our book chapter are that global net carbon dioxide emissions must become negative between 2060 and 2070 in all scenarios This is consistent with the Paris Agreement's goal of "achieving net zero emissions by the second half of this century". Delaying action always means that faster rates of emissions reductions are required which may prove to be technically difficult to achieve and may result in a higher reliance on negative emissions later in the century. If we are really serious about moving towards 1.5^oC then any further delay is not a realistic option.

When we compare the amount of NETs required in both the “well-below 2^oC” and “towards 1.5^oC” scenarios then two things become clear. First, that a 2^oC target can be met with BECCS only, and second, that this is not the case for 1.5^oC, which requires about double the amount of negative emissions. In this instance, even with significant availability of biomass worldwide, substantial amounts of other NETs beyond BECCS will be required. These include direct air capture, afforestation, and advanced weathering, and will need to be about enough to capture between 250–700 Gt CO₂. Therefore the analysis suggests that delaying action makes pursuing the 1.5^oC goal especially difficult without extremely high levels of negative emissions technologies (NETs).

Conclusion: Decision makers must weigh up the risks of different strategies

Policymakers must also realise that the outlook for fossil fuels is closely linked to the prospects for NETs. If NETs cannot be scaled, the levels of fossil fuels suggested in this analysis are not compatible with the Paris Agreement goals. In other words, there are risks of lock-in to a high fossil future. The implications for fossil fuel consumption of delayed ratcheting of commitments are far-reaching, particularly in the medium-term for large coal consumers. What should be noted is the need for wholesale retirement of coal generation capacity and the implementation of lower carbon technologies. Decision makers must, therefore, comprehend fully the risks of different strategies. Implementing this capacity switch now will allow for a smoother transition, particularly given any delay to 2030 requires significantly higher rates of electricity capacity investments between 2030 and 2040. It is also crucial that significantly more attention is paid to demand side efforts in terms of the behavioural drivers of energy use.

For a full copy of the book chapter ‘How Low Can We Go? The Implications of Delayed Ratcheting and Negative Emissions Technologies on Achieving Well Below 2^oC.’ please see link:

The chapter authored by Matthew Winning, Steve Pye, James Glynn, Daniel Scamman and Daniel Welsby is published in: Limiting Global Warming to Well Below 2^oC: Energy System Modelling and Policy Development. Editors: George Giannakidis, Kenneth Karlsson, Maryse Labriet, Brian Ó Gallachóir