Tropospheric Ice in a Warming World

Ice in the atmosphere plays an important role in the climate system by regulating cloud radiative effects, large-scale circulations, and precipitation processes. The change in the ice phase in the atmosphere with global warming, however, is still unclear. Here we show that, while the total mass of global atmospheric ice has remained relatively stable based on satellite measurements since the 2000s, the spatial distribution may have been changing. This view is supported by an ensemble of high-resolution atmospheric model simulations in the tropics that clearly reveal a decrease in ice content in the optically thick anvil cloud areas and an increase in ice content in the convective regions and their peripheral regions. Further analysis based on a state-of-the-art global reanalysis indicates that while the lower tropospheric ice content has decreased with rising melting layer height, ice content has increased in the middle and upper subfreezing troposphere under global warming. This trend is dominated by the increase of falling ice associated with more frequent extreme deep convective events. In contrast, the total mass of global cloud ice has tended to stabilize in recent decades. This study sheds light on the changing pattern of global atmospheric ice obscured by the stable total ice mass, offering a pathway toward constraining cloud feedback mechanisms and climate projections.