20.4: The Atmosphere and Climate Change
The Atmosphere and Climate Change
Once heat radiates off Earth’s surface it travels into the atmosphere. Certain gases in Earth’s atmosphere, called greenhouse gases Links to an external site., allow sunlight to pass but absorb terrestrial energy and radiate it in all directions, including back to the surface of the Earth (Figure 20.7).
Figure 20.7: A simplified animation of the greenhouse effect. (Public Domain; NASA/JPL-Caltech Links to an external site.)
These gases, such as water vapor, carbon dioxide, ozone, and methane, represent a tiny but important fraction of atmospheric material. Different greenhouse gases vary in how effectively they absorb and reradiate energy and in their relative proportions in the atmosphere; a higher concentration of potent greenhouse gases can retain more thermal energy within the atmosphere while the rest of the reflected and radiated energy escapes from the atmosphere and dissipates into space. The proportion of greenhouse gases in the atmosphere has changed dramatically through geologic time as a result of numerous factors influencing the atmospheric system, including the rate of plate motion, amount of volcanism, photosynthesis, weathering of rocks, burning of fossil fuels, and more.
Another major component of our atmosphere are aerosols (sea spray, dust, ash, etc.). Aerosols originate from surficial processes, like the expulsion of ash or sulfur dioxide from volcanoes and the burning of fossil fuels, that can alter climate by reflecting incoming solar radiation before it reaches the Earth’s surface.