Modelling the full Earth system for better climate action
Climate choices made today will shape the planet for centuries. To make them wisely, we need models powerful enough to show us their consequences. Earth system models (ESMs) simulate how the atmosphere, oceans, land and living systems interact, and are among the most important tools for informing climate policy. Yet some gaps remain to support real decision-making. Closing some of those gaps is what the EU-funded ESM2025(opens in new window) project set out to do. The project has developed and tested a new generation of European ESMs, making them better at representing the carbon cycle, methane, land use, wildfires, oceans and ice sheets within a single, consistent framework. As project coordinator Roland Séférian explains, “It is not just about making models more detailed; it is about making them better at answering the questions society is actually asking.”
Bridging two worlds of climate modelling
One of the project’s most significant advances was building a stronger bridge between two modelling worlds(opens in new window) that have traditionally worked apart: ESMs, which simulate how natural systems respond to emissions, and integrated assessment models, which explore how societal and economic choices influence climate outcomes. Connecting these more consistently means critical information is no longer lost as it moves from one model to the other. The ESM2025 project improved the way emissions pathways are translated into warming and carbon-cycle responses. It also ensured a more effective flow of land and climate information through the modelling chain. A key part involved making MAGICC – a fast climate model used to turn emissions pathways into estimates of future warming – available in open-source form; what Séférian calls ‘a big step’ for transparency and wider use.
What improved models reveal about climate action
What improved models reveal about climate action To halt global warming, achieving net-zero CO2 emissions is essential. This was a key confirmation from the ESM2025 project, whose findings(opens in new window) are directly relevant to mitigation and adaptation approaches. The project also demonstrated that methane and other non-CO2 gases are crucial for near-term outcomes. Methane alone accounts for nearly half of current warming and reducing it could produce a measurable cooling effect. In addition, it issued an important caution about land-based mitigation strategies(opens in new window). They can contribute to climate goals, but the Earth system’s own responses can bring side effects or reduce their benefits significantly. For example, large-scale bioenergy crops may remove CO2 but compete with food production and strain water resources. Regional aspects matter too: forests planted in tropical areas tend to cool the climate, while those in high-latitude snowy regions can cause local warming despite absorbing carbon. “There are no shortcuts once you look at the full Earth system,” says Séférian. “Land-based mitigation cannot be treated as a simple fix. These options can help, but they come with uncertainties, trade-offs and regional differences that we need to take seriously.” The ESM2025 project improved five major European ESMs and left behind open tools that make it easier to test real emissions choices against the Paris Agreement goals, influencing the future work of the Intergovernmental Panel on Climate Change and the Coupled Model Intercomparison Project. For Séférian, however, collaboration is among its most important legacies. “ESM2025 united communities that do not usually collaborate so closely, and people are coming away with a real sense that we want to keep working together.” In science, policy assessment and classrooms across Europe, that work is already under way.
