The troposphere is the layer of the atmosphere extending from Earth’s surface to an altitude of 10 to 16 km. It contains the air we breathe. From it falls the water we drink. And through it passes the life producing energy of the sun. It is also the seat of weather and climate. Given the diversity of ecosystems on the Earth, it is likely that the natural troposphere is highly inhomogeneous in its chemical composition.
As the heat energy from sunlight travels through the atmosphere, only a small part of it is trapped by the atmosphere. Most of the heat energy is absorbed by the ground. The ground then warms the air above it. The warm, less dense air rises and is replaced by cooler, dense air. Currents of air that carry heat up into the atmosphere are produced. These air movements are called convection.
There is more water vapor and carbon dioxide in the troposphere than in any other layer. This fact is important because the two gases in question affect the heat balance of the Earth, particularly in the infrared radiation coming from the sun. Water vapor trap much of the infrared that is being reradiated from the sun heated ground. The troposphere, therefore, is heated by the ground as well as by the sun.
Temperature decreases with increasing altitude in the troposphere. The temperature of the troposphere drops about 6.5 degrees Celsius for every kilometer above the Earth’s surface. But at an altitude of about 12 kilometers, the temperature seems to stop dropping.
Much of the solar radiation reaching the Earth is absorbed by the ground, air, clouds, water and ice. The rest is reflected back into space. Much of the short wave radiation from the sun and outer space-ultraviolet, X-rays and cosmic rays is absorbed or scattered in the upper atmosphere before it reaches the troposphere or the ground.
There is increasing evidence that the climate of the Earth is becoming warmer. For one thing, many of the glaciers and ice sheets in the mountains and polar regions seem to be melting away. An increase in the carbon dioxide contained in the atmosphere may be one factor, for this gas behaves as an insulator, retaining much of the sun’s heat that reaches the earth.