Geoscience Reference
In-Depth Information
(nitrogen 78.08 percent, oxygen 20.98 percent,
argon 0.93 percent and carbon dioxide 0.035
percent) had been identified. It had been long
suspected that human activities could have the
potential to alter climate. While the atmospheric
'greenhouse effect' was discovered in 1824 by
Joseph Fourier, the first serious consideration of
a link between climate change, the greenhouse
effect and changes in atmospheric carbon dioxide
also emerged in the late nineteenth century
through the insights of Swedish scientist Svante
Arthenius. His expectation that carbon dioxide
levels and temperature would rise due to fossil
fuel burning has sadly turned out to be correct.
The hair hygrograph, designed to measure
relative humidity (the amount of water vapor in
the atmosphere relative to how much it can
hold at saturation, expressed as a percent), was
invented in 1780 by de Saussure. Rainfall records
exist from the late seventeenth century in England,
although early measurements are described from
India in the fourth century
BC
, Palestine about
AD
100 and Korea in the 1440s. A cloud classification
scheme was devised by Luke Howard in 1803,
but was not fully developed and implemented in
observational practice until the 1920s. Equally
vital was the establishment of networks of
observing stations, following a standardized set of
procedures for observing the weather and its
elements, and a rapid means of exchanging the
data (the telegraph). These two developments
went hand-in-hand in Europe and North America
in the 1850s-1860s.
The greater density of water compared with
that of air (a factor of about 1000 at mean sea level
pressure) gives water a higher specific heat. In
other words, much more heat is required to raise
the temperature of a cubic meter of water by 1
exchanges with the atmosphere is key to under-
standing climate variability. Another important
feature of the behavior of air and water appears
during the process of evaporation or condensa-
tion. As Black showed in 1760, during evapora-
tion, heat energy of water is translated into kinetic
energy of water vapor molecules (i.e., latent heat),
whereas subsequent condensation in a cloud or as
fog releases kinetic energy which returns as heat
energy. The amount of water which can be stored
in water vapor depends on the temperature of the
air. This is why the condensation of warm, moist
tropical air releases large amounts of latent heat
increasing the instability of tropical air masses.
This may be considered as part of the process
of convection in which heated air expands,
decreases in density and rises, perhaps resulting
in precipitation, whereas cooling air contracts,
increases in density and subsides.
The combined use of the barometer and
thermometer allowed the vertical structure of
the atmosphere to be investigated. While it is
common experience to the aviator and mountain
traveler that temperature tends to decrease
with height, the reverse pattern of temperature
increasing with height, known as an inversion, is
also quite common, and in fact dominates in
certain regions and atmospheric levels. A low-
level (i.e., near-surface) temperature inversion
was discovered in 1856 at a height of about 1km
on a mountain in Tenerife. Later investigations
revealed that this so-called Trade Wind Inversion
is found over the eastern subtropical oceans where
subsiding dry high pressure air overlies cool,
moist maritime air close to the ocean surface.
Such inversions inhibit vertical (convective) air
movements and, consequently, form a lid to some
atmospheric activity. The Trade Wind Inversion
was shown in the 1920s to differ in elevation
between some 500m and 2km in different parts of
the Atlantic Ocean in the belt 30°N to 30°S.
Around 1900 a more important continuous and
widespread temperature inversion was revealed
by balloon flights to exist at about 10km at the
equator and 8km at high latitudes. This inversion
C
than to raise the temperature of an equal volume
of air by the same amount. It is interesting to note
that just the top 10-15cm of ocean waters contain
as much heat as does the total atmosphere; the
total heat in the ocean in turn dwarfs that of the
atmosphere. As is now known, this tremendous
reservoir of heat in the upper ocean and its
°
