Global warming is a real, rapidly advancing, and widespread threat facing humanity this century. Climate change is expected to accelerate water cycles and thereby increase the available, renewable freshwater Recent observations suggest that at global scales, rapid environmental changes may be altering the structure, composition and dynamics of forests. Predicted global warming will probably affect range sizes and the geographical distribution of biota. Climatically determined ecotones, arctic and alpine treelines are assumed to be particularly sensitive to altered temperature regimes and climate warming is expected to drive treelines upslope and poleward at the expense of alpine and arctic ecosystems, respectively. Currently, there is much interest in the rate at which the tree line may advance in response to environmental change, especially global warming. The reason for the renewed interest in tree lines is clear: an advancing tree line, or a denser forest below the tree line, would have important implications for the global carbon cycle (increasing the terrestrial carbon sink) and for biodiversity of the alpine ecotone (possibly ousting rare species and disrupting alpine and arctic plant communities).
