In simple terms, trees increase moisture in the atmosphere by the process of evapotranspiration. This is a process by which tree leaves “exhale” moisture in the form of vapor through small openings (stomata). A mature tree pumps about 400 gallons of water per day through it’s vascular tissue, then evaporates most of that into the air. This moisture contributes to cloud formation and precipitation.

Trees also decrease air temperatures by intercepting ultraviolet light, shade, and evaporative-cooling.

“Trees play an important role in Kilimanjaro’s ecosystem by providing moisture through transpiration. Pepin suggests that extensive regional deforestation in recent decades has reduced the flow of moisture up the mountainside, thus speeding up the disappearance of the ice.” –New Scientist