Geoscience Reference
In-Depth Information
Incident solar radiation
340 W m
-2
Reflected solar
radiation 100 W m
-2
Earth's biosphere
and climatic systems
Atmospherically
absorbed solar radiation
240 W m
-2
Radiated infrared energy
240Wm
-2
Fig. 1.1
Asummaryoftheprincipalsolar-energylowandbalanceintheEarth'satmosphere.Notallthehigh-energy
infraredradiationfallingontheEarthisrelectedbackoutintospace.Someisconvertedintolower-energy
infraredradiationintheatmosphere.Theresultisatmosphericwarming.Note:theSunradiates1370Wm
−2
totheEarth'sdistance.However,theEarthisarotatingspherenotalatsurface,sotheaverageenergyfalling
ontheEarth'ssurfaceisjust340Wm
−2
.
is why those constituents of the atmosphere that strongly exhibit these properties
are called greenhouse gases. The Irish polymath John Tyndall described the green-
house role of some gases in 1861 and succeeded in quantifying their heat-absorbing
properties.
There are a number of greenhouse gases. Many of these occur naturally at concen-
trations determined by natural, as opposed to human, factors. Water vapour (H
2
O) is
one, methane (CH
4
) another, as is nitrous oxide (N
2
O), but the one talked about most
frequently is carbon dioxide (CO
2
). Others do not occur naturally. For example, halo-
carbons such as chlorofluorocarbons (CFCs) are completely artificial (human-made),
being products from the chemical industry that are used as coolants and in foam
blowing. Then again, today there are the naturally occurring greenhouse gases, such
as carbon dioxide, the atmospheric concentrations of which are further enhanced by
human action.
Tyndall not only recognised that there were greenhouse gases, he also speculated
what would happen if their concentration in the atmosphere changed. He considered
what it would be like if their warming effect did not take place (as on the Moon).
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