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The cryosphere reacts sensitively to climate change, as evidenced by the widespread retreat of mountain glaciers. Subsurface ice contained in permafrost is similarly affected by climate change, causing persistent impacts on natural and human systems. In contrast to glaciers, permafrost is not observable spatially and therefore its presence and possible changes are frequently overlooked. Correspondingly, little is known about permafrost in the mountains of the Hindu Kush Himalaya (HKH) region, despite permafrost area exceeding that of glaciers in nearly all countries. Based on evidence and insight gained mostly in other permafrost areas globally, this review provides a synopsis on what is known or can be inferred about permafrost in the mountains of the HKH region. Given the extreme nature of the environment concerned, it is to be expected that the diversity of conditions and phenomena encountered in permafrost exceed what has previously been described and investigated. We further argue that climate change in concert with increasing development will bring about diverse permafrost-related impacts on vegetation, water quality, geohazards, and livelihoods. To better anticipate and mitigate these effects, a deepened understanding of high-elevation permafrost in subtropical latitudes as well as the pathways interconnecting environmental changes and human livelihoods are needed.

The Hindu Kush‐Himalayan (HKH) region epitomizes a geographic region where cryospheric processes coupled with hydrological regimes are under threat owing to a warming climate and shifts in climate extremes. In this study, we analyse global climate models in the Coupled Model Intercomparison Project phase 3 (CMIP3) and phase 5 (CMIP5) archives to investigate the qualitative aspects of change and trends in temperature and precipitation indices. Specifically, we examine and evaluate multi‐model, multi‐scenario climate change projections and seven extreme temperature and precipitation indices over the eastern Himalaya (EH) and western Himalaya‐Karakoram (WH) regions for the 21st century. Density distribution plots of observed climate indices for meteorological stations and gridded indices are also analysed, which indicate significant negative trends in the annual number of frost days and significant increasing trends in warm nights in the EH region over the 1960–2000 period. Multi‐model average (MMA) projections additionally indicate continued trends towards more extreme conditions consistent with a warmer, wetter climate. Precipitation projections indicate increased mean precipitation with more frequent extreme rainfall during monsoon season in the EH region, and a wetter cold season in the WH region. Time series of all MMA precipitation indices exhibit significant increasing trends over the 1901–2099 period. By comparison, time series of temperature indices show decreases in the intra‐annual extreme temperature range and total number of frost days, as well as increases in warm nights. In general, these future projections point towards increases in summertime temperatures and modifications in precipitation across both regions.