Mountains become warmer with elevation in response to greenhouse gas warming, an effect known as elevation-dependent warming (EDW). The Eocene is considered a replica of the future climate in an epoch with high atmospheric carbon dioxide concentration (CO2). Therefore, the topographic features of the Eocene strata are of interest. However, obtaining proxy data for mountain regions during the Eocene hothouse is challenging. Paleoclimate model simulation is an effective tool for exploring past climate change. Therefore, we conducted sensitivity experiment simulations employing the Community Earth System Model version 1.2 (CESM1.2) forced by proxy-estimated CO2 levels. This is the first Eocene study demonstrating the elevation-dependent temperature changes and illustrated using the surface energy budget decomposition. Here five major mountain ranges have been chosen based on their paleogeographic continental location. We found a nonlinear response of elevation-dependent temperature change to CO2 concentrations regulated by seasonal variations. The radiative and non-radiative feedback compensation is responsible for the elevation-dependency temperature changes. Our results suggest temperature perturbations regulate elevation-dependent changes in skin temperature through a combination of feedback under greenhouse warming in the early Eocene. These findings also show future paradox response exhibiting elevation-dependent cooling overall mountain regions due to lower elevation warming.

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Himalayas hydroclimate is a lifeline for South Asia’s most densely populated region. Every year flooding in the Himalayan rivers is usual during monsoon, which impacts millions of inhabitants of the Himalayas and downstream regions. Recent studies demonstrate the role of melting glaciers and snow, in the context of global warming, along with monsoonal rain causing recurrent floods. Here, we highlight the interannual variability in the eastern Himalayan hydroclimate as a natural hazard using observed reanalysis for the last 43 years (1979-2021). We found anomalous extreme years with eight dry years and eight wet years after removing the climate change signal. Monsoon rainfall is a significant contributor, and melting snow is not a potential contributor to these anomalous extreme years. The variability of Himalayan monsoonal rainfall is strongly regulated by local monsoonal Hadley circulation associated with Walker circulation. Our findings demonstrate mechanisms associated with Himalayan wet and dry response. The insights provided in this study underscore the impact of natural variability-driven challenging events that could be predictable. Thus, this mechanism could improve the predictability of the Himalayas floods.

Mountains play a vital role in shaping regional and global climate, altering atmospheric circulation and precipitation patterns. To this end, identifying projected changes in mountain precipitation is significantly challenging due to topographic complexity. This study explains how mountain precipitation could respond to rising greenhouse gases. Using a series of century-long fully coupled high-resolution simulations conducted with the Community Earth System Model, we aim to disentangle future changes in mountain precipitation in response to atmospheric carbon dioxide (CO2) perturbations. We identify five low-latitude mountain ranges with elevation-dependent precipitation response, including New Guinea, East Africa, Eastern Himalayas, Central America, and Central Andes. Those mountains are expected to have a mixture of increasing and decreasing precipitation in response to CO2-induced warming, especially over the summit and steep topography. To elucidate the mechanisms controlling future changes in mountain precipitation, we propose ‘orographic moist-convection feedback’ in which an increase in low-level relative humidity enhances local precipitation by strengthening the upward motion through moist processes for the wetting response and vice versa for the drying response. The effects of Mountain precipitation changes can be extended to hydrology and could lead to significant consequences for human societies and ecosystems.