Anthropogenic climate change is causing shifts in the frequencies of extreme weather events. There is an urgent need to quantify future unprecedented risks from extreme temperatures and precipitation, and the geographic distributions of at-risk areas. Here, we define the rim of two-dimensional (2D) risk histograms for 20-year extreme temperatures and precipitation as a climatic risk boundary. We found that nearly a quarter of the world population in South Asia, sub-Saharan Africa, and other

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... ons of the world will transgress the climatic risk boundaries by the end of this century under RCP8.5 scenario, while under the future RCP2.6 scenario, only 5.8% of population will transgress the climatic risk boundaries. Some metropolitan areas, such as Delhi, Mumbai, and Tokyo, will also overstep the boundaries. While many large cities will remain within the climatic risk boundaries, they will still be exposed to unprecedented climatic risks in relation to the experiences of people in that region. This study will help refine public perceptions of extreme climatic risks and lead to more efficient policy making. In the future, unprecedented extreme weather risks should be properly considered in the impact assessments of climate change, and transfers of technologies and experiences gained in other regions to new at-risk regions should be supported to assist with adaptation to extreme climatic risks.