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About the project

Limiting global warming to 1.5°-2°C, as agreed in the Paris Agreement, is becoming increasingly challenging. Policymakers and societies require information about feasible mitigation pathways that realise the Paris Agreement, as well as information on the consequences of temporarily or more permanently exceeding these targets.

OptimESM brings together scientists from different disciplines to provide this information by using the most advanced existing Earth System Models (ESMs), further developing and improving them to produce a new generation of ESMs, and applying these to provide new future climate simulations for a range of new emission scenarios produced by the project Integrated Assessment Models (IAMs). The project started in January 2023 and will run for five years.

OptimESM will progress beyond the state-of-the-art in five key areas:

i) Delivering the next generation of high-resolution ESMs, taking ESMs to the next level by:

Increasing model resolution into the range 25-50 km, to allow a more accurate simulation of key features of the physical climate system in both the atmosphere and the ocean, particularly with respect to their variability and extremes.

Increasing process realism, targeting phenomena thought to be at risk of abrupt change such as continental ice sheets and their interactions with ice shelves, ocean circulation and its interaction with marine ecosystems and carbon uptake, an improved representation of permafrost and the potential release of CH4 and CO2, among other phenomena.

ii) Developing new, policy-relevant emission and land use scenarios

The REMIND-MAgPIE model, one of the IAMs used to derive Shared Socio-Economic Pathways (SSPs) and widely used in the recent AR6 of the IPCC, will be used to develop a range of new land-use and emission scenarios for greenhouse gases and other short-lived climate forcers (SLCFs) that extend to 2100, and for a number of specific scenarios to 2300. These scenarios will reflect the most recent policy decisions, including national pledges on emission reductions, and include scenarios realising the Paris Agreement, and others overshooting the 1.5°C and 2°C targets. In addition, we will develop idealised emission scenarios that maintain global mean temperatures at a number of different warming levels.

iii) Evaluating ESMs and uncertainty in climate projections

We will use a range of new and existing observations to evaluate the simulated climate variability and Earth system phenomena in the new models, with a focus on Earth system processes that likely profit from increased model resolution and those that underpin abrupt changes in our models. OptimESM will quantify uncertainty in the model simulations using both established and innovative methodologies such as using novel model calibration methods and artificial intelligence (AI).

iv) Delivering new knowledge on potential abrupt climate changes

OptimESM will provide new, ground-breaking knowledge on the risk of abrupt changes and tipping points in a range of Earth system phenomena, by analysing both CMIP6 and OptimESM climate projections. The aim is to develop a Catalogue of Abrupt Changes documenting the likelihood of abrupt change in the phenomena studied as a function of emission scenario, global mean warming, rate of warming and the duration of warming above a given target. Such a unique catalogue will help inform mitigation policies aimed at identifying “safe” future pathways to avoid, or reduce the risk of, abrupt change.

v) Delivering new knowledge on regional consequences

OptimESM will provide new understanding of the regional climate response to long-term global change and to the occurrence of different abrupt changes. Our focus will be on Europe and the polar regions, with an emphasis on induced changes in regional climate variability and extreme events. We will link regional changes to specific emission pathways and levels of global mean warming, as well as the degree and duration of a warming overshoot.