Wind, Humidity and Altitude

Three further abiotic factors round out the environment's physical profile. Wind is simply the natural movement of air, driven mainly by differential heating between the equator and the poles together with the planet's rotation (the Coriolis effect); ecologically it disperses pollen and seeds, assists bird flight, is harvested as wind energy, but can also drive erosion, and its speed is measured with an anemometer. Humidity is the invisible water vapour present in the atmosphere, expressed as absolute humidity (total mass of vapour in a given volume of air, independent of temperature) or relative humidity (vapour present as a percentage of what the air could hold at saturation at that same temperature), and is measured with a hygrometer. Altitude, the elevation or gradient of a location, indirectly controls both temperature and precipitation — as altitude increases, temperature and the density of atmospheric oxygen both fall, and higher elevations tend to receive snow rather than rain. Animals can partially compensate for altitude-driven stress through acclimatization, a short-term physiological adjustment; people who mov …