Rapid increase in U.S. influenza epidemics driven by human-induced rapid temperature variations during the autumn transition period

Influenza epidemics have increasingly threatened human lives and socioeconomic development in recent decades. It is widely acknowledged that weather and climate play a vital role in influenza epidemics, however, which specific meteorological factors and to which extent the changes of the factors are responsible for the influenza intensity remains unclear. Previous studies suggest a decreasing trend of influenza intensity with the rise of winter temperature, which is contradictory to the observed enhanced influenza intensity under global warming. This study focuses on the potential contributions of high-frequency climate variability to the changes of influenza intensity in the United States. The results show that, the peak strength of the influenza season increased by 50% from 1997 to 2021 and two-thirds of this increase is associated with the amplified October–November temperature changes between neighboring days (TCN), a measure of high-frequency temperature variability. This association is most evident in the central region of the United States. Based on the ensemble of CMIP6 simulations, an evident increase of TCN by 0.16°C/decade (p < 0.01) is pronounced along with the enhanced warming driven by the reduction of anthropogenic aerosol emissions. The strengthening of the meridional temperature gradient caused by uneven changes in anthropogenic aerosol and greenhouse gas emissions favored immune-related TCN, leading to the intensification of influenza epidemics eventually. Our findings address the need for more thoughtful mitigation and adaptation strategies to minimize the adverse health effects of human-induced climate drivers.