26. The figure shows a comparison of current vegetation zones at a hypothetical dry temperate mountain site with simulated vegetation zones under a climate-warming scenario. Mountains cover about 20% of the Earth's continents and serve as an important water source for most major rivers. Paleologic records indicate that climate warming in the past has caused vegetation zones to shift to higher elevations, resulting in the loss of some species and ecosystems. Simulated scenarios for temperate-climate mountain sites suggest that continued warming could have similar consequences. Species and ecosystems with limited climatic ranges could disappear and, in most mountain regions, the extent and volume of glaciers and the extent of permafrost and seasonal snow cover will be reduced. Along with possible changes in precipitation this would affect soil stability and socio-economic activities such as agriculture, tourism, hydropower and logging. Resources for indigenous populations and recreational activities would also be disrupted.