Amplified or exaggerated changes in perceived temperature extremes under global warming

The perceived temperature has been changing rapidly under global warming, and its related extremes have significant impacts on labor productivity and human health. Although numerous thermal indices have been developed to quantify the perceived temperature, impact assessments have not been conducted comprehensively. The lack of exploring the nonlinearity and linearity inherent in thermal indices will lead to biased conclusions. We conduct a comprehensive investigation of 161 indices to create an ensemble of selected thermal indices that represent the linear and nonlinear relationships of climatic conditions and quantify the changes in the perceived temperature and related extremes. Here we find that the increase in the mean perceived temperature can be strongly exaggerated by using nonlinear indices or linear indices that only consider the combined effect of high temperature and humidity. Wind speed incorporated into the schemes of linear indices can largely offset the increase in the perceived temperature induced by the high relative humidity. These two divergent changes can be further enhanced in future exposure to heat stress. Furthermore, our findings reveal an amplification of heatwave durations induced by the combined effects of multiple variables for all thermal indices. Such an amplification leads to a cascade of relatively short-duration heatwaves evolving into super long-lasting heatwaves which are particularly pronounced over low-latitude areas.