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Summary

The Greenhouse Effect is a natural phenomenon caused by the presence of certain molecules in the Earth's atmosphere (water vapor, Carbon Dioxide, Ozone, Methane...)

The Earth's surface is heated solely by solar energy (geothermal sources are 10,000 times less important).  Half of this solar energy is captured by the Earth, while the rest is absorbed by the atmosphere and, to a small extent, reflected back into space. The Earth, thus heated, itself emits radiation, but in the infrarouge.   The greenhouse gases in the atmosphere absorb  primarily these infrared wavelengths, and re-emit 80% of this energy back toward the Earth. It is this energy trap that we call the Greenhouse Effect.  It is responsible for permitting water in the liquid  state to exist on our planet, and so it favored the development of Life on Earth:  without the Greenhouse Effect, ground temperature would be around -18°C.

But human activities are beginning to disturb this equilibrium by increasing the atmospheric concentrations of several greenhouse gases, most notably Carbon Dioxide (CO2 ) and Methane (CH4).

Click on the percentages to get information.

Learning goals

  • To insist that the Greenhouse Effect is a natural phenomenon that has allowed the appearance of Life on Earth.
  • To distinguish the electromagnetic characteristics of radiations. Those from the Sun are primarily in the high infrared, the visible and the near ultraviolet. Those emitted by the Earth are in the low infrared. Molecules of greenhouse gases are little affected by the former.
  • To mention the certitude of climate change resulting from the release of greenhouse gases. (Source: Work done by The Intergovernmental Panel on Climate Change (IPCC) between 1990 and 1997 (Kyoto). To also recognize the uncertainty about the extent and the rapidity of the changes.
  • To remind people of the call of the Kyoto Protocol: 170 countries have agreed to, by 2012, reduce greenhouse gas emissions to levels 5% lower than those existing in 1990. In the he Paris agreement (12 December 2015) all countries agreed to work to limit global temperature rise to well below 2 degrees Celsius, and given the grave risks, to strive for 1.5 degrees Celsius.

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The atmosphere is composed of 78% Nitrogen (N2), 20.9% Oxygen (O2), 0.9% Argon (Ar) and, in much more diffuse quantities, greenhouse gases,  among which we should make note of, in particular,…

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