GLOBAL-EX: A GLOBAL theory for EXtreme land temperatures in a changing climate

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Extreme hot temperatures are increasing in frequency and intensity as climate warms. The impacts of extreme heat are widespread and severe, with parts of the world potentially becoming uninhabitable by the end of this century. Yet the future of extreme temperatures is highly uncertain: Climate models project a wide range of responses, making it difficult to prepare for the escalating effects of extreme heat. This large uncertainty is compounded by the lack of a global theory for extreme temperatures in a changing climate, representing a fundamental challenge to our understanding of the climate system with critical societal impacts.GLOBAL-EX will combine a hierarchy of simulations, observational analyses and physical theory to transform the state of the art in the science of extreme temperatures. The overarching goal is to build a global theory for extreme temperatures over land in a changing climate. Two steps are required to achieve this goal: First, I will perform idealised simulations spanning a wide range of climate states to identify the large-scale constraints imposed by atmospheric dynamics on extreme-temperature events. Second, I will use novel regional simulations together with analyses of observational data to decompose the processes controlling land humidity on hot days, which are tightly coupled to extreme temperatures. The new theory will be applied to quantify the drivers of trends in extreme temperatures over recent decades and to understand the behaviour of extreme heat in response to future changes in greenhouse gas concentrations. Not only will this project provide a major step forward in our fundamental understanding of the climate system, GLOBAL-EX is also expected to identify new pathways to narrowing large uncertainties in projections of extreme temperatures, with benefits for vulnerable societies throughout the world.