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Understanding Climate Change in Mountains, Mel Reasoner, Ray Bradley and Bruno Messerli

Mountain regions provide critical goods
and services, not only to mountain inhabitants
but also to lowland communities


The functioning of fragile mountain systems is threatened today by an array of anthropogenic changes, including land use and land cover changes, acidic deposition, increasing atmospheric CO2 concentrations and climatic change. The combination of high rates of environmental change and increasing economic pressure is significantly affecting the ability of many of the world’s mountain regions to provide critical goods and services, not only for mountain inhabitants but also for lowland communities. Considering the disproportionately large number of goods and services that derive from mountain regions, it is critical to understand how the flow of these may be affected by the environmental changes predicted for the twenty-first century.


In its third assessment, the Intergovernmental Panel on Climate Change (IPCC) produced a series of future climate scenarios, based on a number of General Circulation Models. A common feature of these models is that the anticipated warming of the next several decades is expected to be more pronounced in northern high latitudes. A less obvious feature of these IPCC scenarios is that the pattern of warming in the atmosphere is also expected to be more pronounced at progressively higher elevation in the troposphere, along a latitudinal gradient from the Arctic to approximately 30° south of the equator. This has profound implications for mountain regions because many mountainous areas are situated in the high-altitude zone of anticipated enhanced warming (Figure 1). A number of independent lines of evidence have indicated that the Arctic is already warming at a higher rate than other parts of the globe. The rapidly thinning Arctic ice pack and increasing thaw penetration into permafrost are two prominent examples of climate change impacts in the western Arctic, which is warming at a rate three to five times faster than the rest of the world.

Figure 1. Topographic transect through the western Cordillera of the Americas, superimposed on General Circulation Model-based estimates of zonally averaged mean annual temperature changes expected with two CO2 levels

Key: Green line shows freezing level.
Note that the largest expected changes are at high latitudes near the surface, and in mid- to low latitudes at higher elevations.

Source: Cubasch, U., Meehl, G.A., Boer, G.J., Stouffer, R.J., Dix, M., Noda, A., Senior, C.A., Raper, S. & Yap, K.S. 2001. Projections of future climate change. In: J.T. Houghton, Y. Ding, D.J. Griggs, M. Noguer, P.J. van der Linden, X. Dai, K. Maskell and C.A. Johnson (eds). Climate Change 2001: The Scientific Basis. Contribution of Working Group I to the Third Final Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge, UK, and New York NY, USA: Cambridge University Press. 881p.


The rapidly receding alpine glaciers in tropical mountains, such as Quelccaya (Andes), Kilimanjaro (Kenya), and the Dasuopu glacier (Himalayas), suggest that enhanced warming may also be occurring at high-elevation sites in lower latitudes, which would be consistent with IPCC model predictions. However, very few high-elevation meteorological stations sites are situated at altitudes that would be appropriate for monitoring this issue. For example, a transect along the crest of the North and South American Cordillera (Figure 2) shows a large observational data gap in mountainous regions between approximately 40°N and 30°S. Although this gap is filled, at least in part, with climatic information obtained from radiosonde measurements, significant discrepancies between radiosonde data and mountain surface data have been observed. Greater warming (and greater increases in freezing-level height) have been recorded at tropical mountain locations than at similar altitudes from radiosonde information above low-elevation stations. It is therefore clear that direct measurements at high-elevation sites are required to assess climatic impacts in mountain environments, and to untangle the climatic and direct anthropogenic drivers.

Figure 2. The current Global Climate Observing System (GCOS) surface network plotted by elevation and latitude along a transect of the North and South American Cordillera. The freezing level is the same as in the previous figure for reference. Note the large observational "data gap" in the mountain zone from ca 40°N to 30°S.


A complex mix of physical and socio-economic factors currently affects fragile mountain environments and these impacts are in turn likely to have substantial direct and indirect consequences for large segments of humanity. It is therefore imperative that the impacts of climate change in the world's mountain regions are well understood. This understanding will remain elusive unless the rather sparse current network of high-elevation monitoring sites is supplemented by additional long-term monitoring sites in the world's mountain regions.

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