Research progresses and prospects of multi-sphere compound extremes from the Earth System perspective

Compound extremes, whose socioeconomic and ecological impacts are severer than that caused by each event occurring in isolation, have evolved into a hot topic in Earth Science in the past decade. In the context of climate change, many compound extremes have exhibited increasing frequency and intensity, and shown novel fashions of combinations, posing more pressing demands and tougher challenges to scientific research and disaster prevention and response. This article, via a perspective of multi-sphere interactions within the Earth System, systematically reviews the status quo, new scientific understanding, and deficiencies regarding the definition, mechanism, change, attribution, and projection of compound extremes. This study also sorts out existing challenges and outlines a potential roadmap in advancing the study on compound extremes with respect to data requirement, mechanistic diagnosis, numerical modeling, attribution and projection, risk assessment, and adaptive response. Further directions of compound extremes studies and key research topics that warrant multi-disciplinary and multisectoral coordinated efforts are also proposed. Given that climate change has reshaped the type of extremes, a transformation from the traditional single-event perspective to a compound-event perspective is needed for scientific research, disaster prevention and mitigation, and climate change adaptation, calling for bottom-up innovation in research objects, ideas, and methods. This article will add value to promoting the research on compound extremes and interdisciplinary cooperations.