The variable gases, while small in amount, play major roles in weather and climate. Pressure is a measure of the mass of the atmosphere above us, therefore pressure decreases with height.
Barometers measure pressure.
Temperature varies with height in the atmosphere. Layers of the atmosphere are associated with the average vertical temperature profile. The rotation of the earth destroys this simple pattern and results in complex, spiral-like wind patterns. Cool air can hold less water than warm air. Rising air cools, so clouds and precipitation are regions of rising air.