Page 7 - SGG_220316_Teachers_Handbook_Module_7

Version for older students

When short-wave radiation from the sun reaches Earth, most of it passes straight
through and hits the surface. The Earth absorbs most of this radiation and gives off
longer-wavelength infrared radiation.

The greenhouse gases absorb some of this infrared radiation, instead of it passing
straight out into space. The atmosphere then emits radiation in all directions, sending
some of it back to the surface, causing the planet to heat up. This process is known as
the 'greenhouse effect'.

NASA – Graphic: The Greenhouse Effect

https://climate.nasa.gov/climate_resources/188/graphic-the-greenhouse-effect/

The greenhouse effect is the phenomenon of the increase of the temperature of a planet by
greenhouse gases present in its atmosphere (compared to a situation in which there are no
greenhouse gases). It raises the temperature of the Earth's surface by 33°C. Without the greenhouse
effect, our planet would be all ice-bound, and the average temperature would be -18°C instead of
+15°C. Without greenhouse gases and their warming effect, we wouldn't be able to survive.

These heat-trapping gases, called greenhouse gases, come from both human and natural sources.
Greenhouse gases like carbon dioxide, methane, and nitrous oxide naturally occur in the atmosphere.
Others, such as halocarbons, are only produced by human activity.

Carbon dioxide originates from volcanic eruptions, the burning of fossil fuels, plant decay, and animal
respiration. Carbon dioxide is also produced by such human activities as land-use change and
deforestation resulting in the release of carbon stored in biomass and less carbon accumulation in soil
and biomass.

Methane originates from the decomposition of organic matter and it can be found in the gas and coal
mines, and in wetlands. The majority of methane emissions come from such human activities as mining
(coal, natural gases, oil) and agriculture (rice cultivation and stomach fermentation in animals).

Nitrous oxide originates from the bacterial decomposition of the earth’s soils and oceans. Humans
increase the amount of nitrous oxide in the atmosphere through land-use change (e.g. cutting down
trees to make space for farming), the use of fertilizers and the burning of fossil fuels.

Halocarbons are produced only by human activities. Chlorofluorocarbons (CFCs), a type of
halocarbons, were widely used in spray cans, cleaners, air conditioners, and refrigerators. After
regulating CFCs, which caused the depletion of the ozone layer, the substitute – hydrofluorocarbons
(HFCs), another type of halocarbons, were introduced. While HFCs do not cause depletion of the ozone
layer, they are greenhouse gases and contribute to the greenhouse effect.

This project has been funded with support from the European Commission. This communication reflects the
views only of the author, and the Commission cannot be held responsible for any use which may be made of the

information contained therein.