336 Glossary
molecules of greenhouse gasesinstead of being retransmitted out to space, thus
warming the atmosphere. The name comes from the ability of greenhouse glass
to transmit incoming solar radiation but retain some of the outgoing thermal
radiation to warm the interior of the greenhouse. The ‘natural’ greenhouse
effect is due to the greenhouse gases present for natural reasons, and is also
observed for the neighbouring planets in the solar system. The ‘enhanced’
greenhouse effect is the added effect caused by the greenhouse gases present in
the atmosphere due to human activities, such as the burning offossil fuelsand
deforestation
Greenhouse gas emissions The release ofgreenhouse gasesinto the atmosphere,
causingglobal warming
Greenhouse gases Moleculesin the Earth’satmospheresuch ascarbon dioxide
(CO 2 ), methane (CH 4 ) and CFCs which warm the atmosphere because they
absorb some of thethermal radiationemitted from the Earth’s surface (see the
greenhouse effect)
GtC Gigatonnes of carbon (C) (1 gigatonne= 109 tonnes). 1 GtC= 3 .7Gt
carbon dioxide
GWP Global warming potential: the ratio of the enhancedgreenhouse effectof
any gas compared with that ofcarbon dioxide
Heat capacity The amount of heat input required to change the temperature of a
substance by 1◦C. Water has a high heat capacity so it takes a large amount of
heat input to give it a small rise in temperature
Hectopascal (hPa) Unit of atmospheric pressure equal tomillibar. Typical
pressure at the surface is 1000 hPa
Hydrological (water) cycle The exchange of water between the atmosphere, the
land and the oceans
Hydro-power The use of water-power to generate electricity
IPCC Intergovernmental Panel on Climate Change – the world scientific body
assessingglobal warming
Isotopes Different forms of anelementwith different atomic masses; an element
is defined by the number ofprotonsits nucleus contains, but the number of
neutronsmay vary, giving different isotopes. For example, the nucleus of a
carbon atom contains six protons. The most common isotope of carbon is^12 C,
with six neutrons making up an atomic mass of 12. One of the other isotopes is(^14) C, with eight neutrons, giving an atomic mass of 14. Carbon-containing
compounds such ascarbon dioxidewill contain a mixture of^12 C and^14 C
isotopes. See alsodeuterium, tritium
Latent heat The heat absorbed when a substance changes from liquid to gas
(evaporation), for example when water evaporates from the sea surface using
the Sun’s energy. It is given out when a substance changes from gas to liquid
(condensation), for example when clouds are formed in theatmosphere
Milankovitch forcing The imposition of regularity on climate change triggered
by regular changes in distribution ofsolar radiation(seeMilankovitch theory)
Milankovitch theory The idea that major ice ages of the past may be linked with
regular variations in the Earth’s orbit around the sun, leading to varying
distribution of incomingsolar radiation