Beyond net zero: integrating extreme risks from climate overshoot into the long-term global goal in order to minimise climate risk

In 2015 a long-term global goal was established in the Paris Agreement to limit global warming to 1.5C above pre-industrial levels. Given the current rates of climate change and the progression of climate policies in the world, it is increasingly likely that the planet will initially overshoot this target. At the same time, a growing body of research has identified that there are elements of the Earth system that may be at risk of undergoing irreversible runaway changes if certain tipping points are crossed; some of these are now understood to exist around warming levels of 1.5-2C, far lower than estimated 20-years ago (5-6C).

Therefore, overshooting the long-term global climate goal, even temporarily, may induce a much larger risk to society and ecosystems than previously anticipated. These risks are both under-researched, and inadequately represented in the scenario planning that supports climate negotiations and policy development.

These scenarios are informed by integrated assessment models that represent interactions between society and the physical climate. These scenarios could be improved by embedding new models of tipping points into integrated assessment modelling, which may enable the risks and uncertainties of tipping points to be more comprehensively accounted for alongside the global temperature goal when developing strategies to optimise global climate outcomes.

As a result, novel climate policies will be designed, and assessed as to whether they are more capable of steering the planet away from tipping points than existing climate policies that don't directly account for those risks. The implications of these novel policies for the required timing and scale of emissions reductions, removals, and other mitigation measures, can then be explored, with potential significance for global decision-making over both short and long timeframes

Aims and Objectives Therefore, given: 1. meeting the current 1.5C long term global goal will likely entail initial overshoot, 2. crossing tipping thresholds is therefore plausible but highly uncertain, and

3. these extreme climate impacts resulting from overshoot are under-researched, and under-represented in scenario planning, the main objectives of this research will be to answer the following questions:

1. Decision-theory: How might existing global decision-making frameworks be extended to account for risks and uncertainty from tipping points in the Earth System?

2. Policy design: To what extent are policies that consider uncertainty from tipping points ex-ante theoretically able to minimise risk more robustly than existing net zero pathways?

3. Mitigation ramification: What are the short-, medium-, and long-term implications for mitigation strategies when these risks and uncertainties are integrated into decision-making?

4. (Bonus) Towards operationalisation: How might gaps be closed between idealised modelling experiments and an operational system that supports global decision-making in the real world?