Desert ecology is the study of interactions between both biotic and abiotic components of desert environments. A desert ecosystem is defined by interactions between organisms, the climate in which they live, and any other non-living influences on the habitat. Deserts are arid regions that are generally associated with warm temperatures; however, cold deserts also exist. Deserts can be found in every continent, with the largest deserts located in Antarctica, the Arctic, Northern Africa, and the Middle East. Climate Deserts experience a wide range of temperatures and weather conditions, and can be classified into four types: hot, semiarid, coastal, and cold. Hot deserts experience warm temperatures year round, and low annual precipitation. Low levels of humidity in hot deserts contribute to high daytime temperatures, and extensive night time heat loss. The average annual temperature in hot deserts is approximately 20 to 25 °C, however, extreme weather conditions can lead to temperatures ranging from -18 to 49 °C. Rainfall generally occurs, followed by long periods of dryness. Semiarid deserts experience similar conditions to hot deserts, however, the maximum and minimum temperatures tend to be less extreme, and generally range from 10 to 38 °C. Coastal deserts are cooler than hot and semiarid deserts, with average summer temperatures ranging between 13 and 24 °C. They also feature higher total rainfall values. Cold deserts are similar in temperature to coastal deserts, however, they receive more annual precipitation in the form of snowfall. Deserts are most notable for their dry climates; usually a result from their surrounding geography. For example, rain-blocking mountain ranges, and distance from oceans are two geographic features that contribute to desert aridity. Rain-blocking mountain ranges create Rain Shadows. As air rises and cools, its relative humidity increases and some or most moisture rains out, leaving little to no water vapor to form precipitation on the other side of the mountain range. Deserts occupy one-fifth of the Earth's land surface and occur in two belts: between 15° and 35° latitude in both the southern and northern hemispheres. These bands are associated with the high solar intensities that all areas in the tropics receive, and with the dry air brought down by the descending arms of both the Hadley and Ferell atmospheric circulation cells. Dry winds hold little moisture for these areas, and also tend to evaporate any water present. Many desert ecosystems are limited by available water levels, rather than rates of