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Greenhouse effect
The Earth’s atmosphere is composed of a variety of gases, some constant and some variable. Variable gases, such as water vapor and carbon dioxide, play an important role in influencing the Earth’s average temperature. These gases are referred to as greenhouse gases (GHG), because they act like the glass on a greenhouse: they allow solar radiation in through the atmosphere, but prevent the escape of all of the counter radiation back out into space. These greenhouse gases absorb counter radiation and emit it back towards the Earth, causing a warming of the lower atmosphere.
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Figure 1: The Greenhouse Effect. Incoming solar radiation passes through the atmosphere, where some of it is reflected back into space, and some is absorbed by the Earth’s surface. The Earth emits longwave counter radiation, some of which is dissipated out through space, while some of it is absorbed by greenhouse gases and emitted back to Earth. (1)
This naturally occurring process is an important part of the planet’s ability to maintain an average temperature that is capable of supporting life on Earth as we know it. Without this process, the Earth would be a very different place: the average temperature of the atmosphere near the surface would be approximately -18°C, as opposed to the average temperature of approximately 14°C observed today (2). The Greenhouse Effect is thus critical to maintaining life on our planet.
What is not natural is the rate at which humans are adding additional greenhouse gases to the atmosphere. This process is referred to as the Enhanced Greenhouse Effect, and is responsible for triggering and enhancing the current warming trend.
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Enhanced Effect
The Greenhouse Effect is an important, naturally occurring process that allows life to thrive on Earth. Humans are, however, causing warming to occur on a global scale by causing the release of additional greenhouse gases into the atmosphere. These additional greenhouse gases are responsible for altering the natural balance of the Greenhouse Effect. As more greenhouse gases are produced, they accumulate in the atmosphere, and are thus available to absorb longwave counter radiation. More radiation is thus radiated back towards Earth, causing an enhanced degree of warming. This process is what we are currently observing today: humans are producing increased amounts of greenhouse gases, which in turn are causing the surface and lower atmosphere to warm.
