Why does temperature decrease when altitude increases?

Temperature decreases with altitude primarily due to how the Earth's atmosphere is warmed and how atmospheric pressure changes. Here are the key reasons:

1. Atmospheric Warming from Below: The Earth's surface absorbs solar radiation and then heats the air above it through conduction and convection. This process warms the troposphere, the lowest layer of the atmosphere, from the bottom up rather than from the top down. As you ascend, you move away from this heat source, leading to cooler temperatures2.

2. Decrease in Atmospheric Pressure: As altitude increases, the weight of the air above decreases, resulting in lower atmospheric pressure. This decrease in pressure causes air molecules to spread out, which leads to cooling because the air expands and its temperature decreases13.

3. Concentration of Greenhouse Gases: Greenhouse gases like water vapor and carbon dioxide, which help retain heat, decrease in concentration with altitude. This reduction in greenhouse gases contributes to lower temperatures at higher elevations4.

4. Lapse Rate: The standard lapse rate, which is the rate at which temperature decreases with altitude, is about 9.8°C per 1,000 meters (or 5.4°F per 1,000 feet) under dry conditions. This rate can vary depending on weather conditions, such as precipitation, which can slow down the cooling effect13.