Control of the temperature and humidity of an environment is obtained by injecting a large volume of water droplets into the air with a major portion of the water droplets being in the range of from about 5 to 50 microns in diameter and with an average diameter in the range of from about 10 to 30 microns. In one embodiment such environmental control is employed for cooling an outdoors area wherein the droplets provide evaporative cooling. When temperatures are low a fog of water droplets essentially opaque to infrared is provided as a cover to crops for preventing frost damage. In another embodiment means for injecting water droplets are arranged within a roofed shelter having sides open at the top and bottom for permitting air circulation. In another embodiment a visible cloud is provided for decorative effect or as a medium on which an image can be projected. Fog having droplets in the above-mentioned size range is produced by impacting a stream of water having a diameter in the range of from about 125 to 400 microns at a velocity in excess of about 135 feet per second against a smooth, solid surface. Such impact causes the stream of water to separate into droplets in the selected size range. In one embodiment a nozzle having an orifice in the range of from about 125 to 400 micron diameter and operated at a pressure in excess of about 350 psi is used to create a water jet. A flat surface having substantially the same diameter as the orifice, normal to the orifice, closely aligned with the orifice, and spaced only a short distance from the orifice is employed for impacting the stream coming out of the orifice. In another embodiment a surface having compound convexity is arranged in front of the orifice at a distance of up to about four millimeters. A complete system involves a large plurality of such nozzles supplied with water substantially free of particles having a size larger than about 1/10 the diameter of the orifice, and at a pressure in excess of about 350 psi. Automatic control of such a system in response to temperature and wind velocity and direction is also provided.