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The Greenhouse Effect

Imagine a greenhouse made of glass. Inside the greenhouse, it will be warmer than outside, allowing gardeners to grow plants that aren’t hardy enough for the natural climate for that region.

Plants are growing in this greenhouse, despite the cold temperatures and icy, snowy conditions outside.
Plants are growing in this greenhouse, despite the cold temperatures and icy, snowy conditions outside.

 

The Greenhouse Effect describes the process where Earth’s Troposphere is heated enough to support life. There are five basic steps to the Greenhouse Effect:

  1. Incoming Short Wave (SW) radiation (i.e. solar energy) arrives at Earth from the sun. Some is scattered, some is reflected, but most of this energy (~45%) is absorbed by Earth's surface.
  2. The absorbed SW radiation changes to heat energy (i.e. Longwave/LW radiation) inside the Earth.
  3. Earth emits LW radiation back outwards. This emitted heat energy warms Earth's surface and the lower atmosphere.
  4. Two things can happen at this point:
    1. Some LW radiation 'escapes' out into space.
    2. Some LW radiation is absorbed then re-emitted by gases in Earth's lower atmosphere.
  5. The LW radiation trapped by Earth's atmosphere warms Earth's surface and the lower atmosphere. 

 

Most solar radiation is absorbed by the Earth's surface and warms it. Some infrared radiation emitted by Earth passes through the atmosphere, while some is absorbed and re-emitted by greenhouse gases in the atmosphere. The effect of this is to warm Earth's surface and the lower atmosophere (troposphere). This process is Earth's Greenhouse Effect.
Most solar radiation is absorbed by the Earth's surface and warms it. Some infrared radiation emitted by Earth passes through the atmosphere, while some is absorbed and re-emitted by greenhouse gases in the atmosphere. The effect of this is to warm Earth's surface and the lower atmosophere (troposphere). This process is Earth's Greenhouse Effect.

 

The Greenhouse Effect is a necessary process for supporting life on Earth.

 

Earth’s average temperature is 15 degrees Celsius/59 degrees Fahrenheit. Without the greenhouse effect, Earth’s temperature would be about 35 degrees Celsius cooler, or -18 degrees Celsius/0 degrees Fahrenheit on average!

 

Greenhouse Gases

So what role do greenhouse gases play in the Greenhouse Effect?

You have probably heard the term ‘greenhouse gases’ or ‘greenhouse gas emissions’ used in reporting on human-induced climate change. As covered earlier, different gases absorb and reflect different wavelengths.

Greenhouse gases are gases found in the atmosphere that absorb Earth’s emitted heat energy – not incoming solar energy. This is how the Greenhouse Effect works!

Greenhouse gases in the atmosphere absorb most of Earth’s emitted heat energy, which heats the lower atmosphere. In turn, the warmed atmosphere helps keep Earth’s surface warm and generally comfortable.

Some of the most common greenhouse gases are:

  • Water Vapor (H20) – typically ranges between 0% and 4%
  • Carbon Dioxide (CO2)
  • Methane (CH4)
  • Nitrous Oxide (N2O)

Potent greenhouse gases like Carbon Dioxide, Methane, and Nitrous Oxide all do exist naturally – the Greenhouse Effect wouldn’t function without them! For example, natural sources of Carbon Dioxide include volcanic eruptions, plant respiration (plants ‘exhaling’), and natural fires. Natural sources of methane include the anaerobic (low/no oxygen) decay of organic material in wetlands and bogs, and fermentation in the digestive tracts of ruminant animals (i.e. cow farts). Nitrous Oxide can be found in some animal waste.