Harald Pauli and Stephan R.P. Halloy
High mountains (i.e., mountains that reach above the climatic treeline) are regions where many interests converge. Their treeless alpine landscapes and ecosystems are key areas for biodiversity, they act as water sources and reservoirs, and they are cultural and religious icons. Yet, mountain environments are threatened by global stressors such as land use impacts and anthropogenic climate change, including associated species redistributions and invasions. High mountains are warming faster than lower elevations. The number of frost days is declining, glaciers are retreating, and snow is remaining for shorter periods, while CO2 partial pressure is increasing. All of these factors affect the way in which ecosystems prosper or degrade.
Thanks to the compression of thermal belts and to topographic ruggedness that favors habitat heterogeneity, mountains have a high diversity of biotic communities and species richness at the landscape level. In tropical to temperature regions, high mountains are biogeographically much like islands. With small habitat areas, species tend to be distributed patchily, with populations evolving independently from those on other isolated summits. Although high mountain areas strongly differ in size, geological age, bedrock, glacial history, solar radiation, precipitation patterns, wind exposure, length of growing season, and biotic features, they are all governed by low-temperature conditions. Combined with their distribution over all climate zones on Earth, mountain habitats and their biota, therefore, represent an excellent natural indicator system for tracing the ecological impacts of global climate change. As temperatures rise, plants and animals migrate upward (and poleward). Plant and animal populations on small, isolated mountains have nowhere to go if climates warm and push them upslope. On the other hand, habitat heterogeneity may buffer against biodiversity losses by providing a multitude of potential refugia for species which become increasingly maladapted to their present habitats.
Global-scale approaches to monitor climate and biotic change in high mountains as well as modeling and experimental studies are helping explain the nature of these changes. Such studies have found that species from lower elevations are colonizing habitats on mountain summits at an accelerating pace, with five times faster rates than half a century ago. Further, repeated in situ surveys in permanent plots showed a widespread transformation of alpine plant community assemblages toward more warmth-demanding and/or less cold-adapted species. Concurrently to widespread increases in overall species richness, high-elevation plant species have declined in abundance and frequency. Strongly cold-adapted plant species may directly suffer from warmer and longer growing seasons through weak abilities to adjust respiration rates to warmer conditions. Combined effects of warming and decreasing water availability will amplify detrimental effects of climatic stresses on alpine biota. Many of the dwarf and slow-growing species, however, will be affected when taller and faster-growing species from lower elevations invade and prosper with warming in alpine environments and, thus, threaten to outcompete locally established species. Warming conditions will also encourage land use changes and upward movement of agriculture, while loss of snow is a loss to ski fields and scenic tourism.
Guoyu Ren, Guoli Tang, and Kangmin Wen
Based on a dataset of national reference and basic stations, which have been quality controlled and inhomogeneity processed, updated surface air temperature (SAT) series of the past 67 (1951–2017) and 113 (1905–2017) years for mainland China are constructed and analyzed. The new temperature series show significant warming trends of 0.24°C/10yr and 0.09°C/10yr respectively for the two periods. The rapid regional warming generally begins from the mid-1980s, about a decade later than the northern hemisphere average SAT change. Warming during the period of 1951–2017 is larger and more significant in the northeast, north, northwest and the Qinghai-Tibetan Plateau, and the most significant SAT increase usually occurs in winter and spring except for the Qinghai-Tibetan Plateau where winter and autumn undergo the largest warming. The slowdown of the warming can be clearly detected after 1998, especially for autumn and winter. The effect of urbanization on trends of the region averaged annual and seasonal mean SAT as calculated from the national reference and basic stations has not been adjusted, despite it being generally large and significant. In north China, the increasing trend of annual mean SAT induced by urbanization for the national stations is 0.10°C/10yr for the period 1961–2015, accounting for at least 31% of the overall annual mean warming. The contribution of urbanization to the overall warming of the past half century in Mainland China has also been summarized and discussed referring to the previous studies.