The troposphere is the lowest level of Earth's atmosphere, and is where all weather phenomena occur. The temperature of the troposphere varies with altitude, and is generally warmest near the surface and coldest at the top. The average temperature at sea level is about 15 degrees Celsius (59 degrees Fahrenheit), while the average temperature at the top of the troposphere is about -56 degrees Celsius (-69 degrees Fahrenheit). The troposphere is also where most of the Earth's water vapor is located.