Abstract
Mountains and high elevation regions are often viewed as climate change “hotspots” which are responding particularly rapid to global climate forcing and may anticipate or amplify what is occurring elsewhere. Accelerating mountain climate change has widespread impacts ranging from an enhanced loss of snow and ice, through impacts on the hydrological regimes, to changes in ecological zonation as species move uphill. We examine global evidence for elevation contrasts in temperature trends (also known as elevation-dependent warming, EDW) and precipitation changes. We performed a meta-analysis of existing studies, which used in-situ station temperature and precipitation data from mountain regions as reported by the IPCC, and we analysed global gridded datasets (observations, reanalyses and model hindcasts). In both cases, we examined the elevation dependency of temperature and precipitation changes since 1900. The meta-analysis indicates that studies using pairs of station groups (in mountains and nearby low elevation areas) show a tendency towards enhanced warming at higher elevations. However, when all past studies of observations are combined globally, no systematic difference in warming rates for high vs. low elevation groups is found. Thus, on a global scale, local and regional features may obscure EDW. Precipitation changes in mountain areas based on station data are inconsistent, and a global elevational gradient in precipitation trends does not emerge. Gridded datasets (CRU, GISTEMP, GPCC, ERA5, CMIP5) show increased warming rates at higher elevations in specific regions (e.g. Andes for CMIP5 and Greater Alpine Region for ERA5), but again, there is no universal amplification of warming in mountains. The agreement between datasets is weak for temperature. Changes in precipitation show a tendency towards weaker (stronger) increase at higher (lower) elevations, especially in mid-latitudes. This means that the orographic effect may be weakening on a global scale, which may be a result of both thermodynamics and changes in atmospheric circulation.