Abstract:

Assessments of IPCC AR6 and SROCC show that the global warming rate in High Mountain (HM) regions has increased recently. Since the 1980s, the warming rate in the High Mountain Asia (HMA) has been significantly higher than the average of the global mountains and that in other high mountains. The warming is generally altitudinal dependent, but the mechanism keeps complex and there are large regional differences. Except for the Rocky Mountains, the warming magnitude in other high mountain areas will increase with altitude to varying degrees. Although the global annual precipitation in mountain areas in the past few decades has shown no obvious trend, it is projected that the annual precipitation in many Northern Hemisphere mountain regions will increase by 5%-20% by the end of the 21st century, with great spatial and temporal discrepancies of extreme rainfall. The frequency and intensity of extreme rainfall will increase over the Qinghai-Tibet Plateau and the Himalayas. The decrease of annual maximum snow water equivalent in mountains is stronger in the altitude zone that solid precipitation is transforming towards liquid precipitation, and the change of mountain snow in the future is not only related to the emission scenario, but also closely related to the altitude. Global mountain glacier mass loss from 2010 to 2019 was greater than that in any other decade since observational records began. Although the rate of mass loss in HMA is smaller, the total ice volume loss is second only to that in the Southern Andes among global main mountain regions. It is projected that mountain glacier retreat will continue for decades or hundreds of years in the future, and the corresponding contribution to the sea level rise will be the largest in HMA among the four HM regions. The permafrost temperature and the thickness of active layer in mountains have been found increased and decreased, respectively. In the future, mountain permafrost will become more unstable with continued and accelerated degradation. Even under the low greenhouse gases emission scenario, the permafrost area on the Qinghai-Tibetan Plateau is expected to decrease by 13.4% to 27.7% by the end of the 21st century. However, from the perspective of the completeness and confidence level of the above assessment, there are still huge gaps in observations and researches in the mountains.

The observing networks in mountains do not always follow standard observation procedures and are often not dense enough to capture fine-scale changes and potentially large-scale patterns. The discrepancies between satellite retrieval data and ground-based observations exist widely, especially for snow cover, which is still a recognized challenge. Therefore, immediate actions should be taken to strengthen the density of mountain observations, especially in three-dimensional space, in accordance with WMO standards, so as to improve the capacity of climate monitoring and services in mountain areas. In terms of information extraction from observations, refined, three-dimensional and accurate climate monitoring and assessment information is urgently needed to provide highly applicable scientific support for disaster management and climate change response.

Projections of future climate change are made through global climate models, regional climate models, or their simplified versions, which are dynamically consistent in the way of representing physical processes and hence link changes in mountains with large-scale atmospheric forcing. However, existing models that specialized for mountain studies usually cover only a single mountain range, and there have been no initiatives such as model inter-comparison programs or coordinated downscaling trials addressing problems existing in mountains climate change.

As a result, the direction of the future researches for mountain climate change lies, on the one hand, in the perspective of natural science, that is to continue to extract reliable information from observation data, support to improve the model resolution and simulation capability for complex underlying surfaces and quantify the contribution of mountain climate change in energy, water and carbon cycle and feedbacks from both macro and micro levels. On the other hand, from the perspective of supporting social sustainable development, to identify the climate change indicators that affect the stability of mountain society and ecosystem, supporting adaptation and mitigation of mountain climate change.

Key words: Mountain, IPCC, Climate change, Cryosphere, Snow, Glacier, Permafrost