612
Climatic Geomorphology
oceanic water, which constitutes an enormous reservoir of CO2, and marine biota play an
important role on the regulation dynamics of atmospheric CO2. Carbon dioxide flux in
the oceans depends on CO2 pressure, atmospheric concentration of CO2, and on surface
winds. Carbon dioxide pressure is controlled by oceanic transport processes, geochemical
processes, and biological processes in the top part of the oceans. Furthermore, solar flux
and latent calorific flow have an influence, as do the above-mentioned factors, in climate
modelling. Therefore, the system is very complex and the models of the flows in the
ocean-atmosphere inter-phase can be subject to large errors (Dickinson et al., 1996).
Moreover, there is limited knowledge on the temperature and salinity of deep waters, close
boundaries between currents, ocean eddies, and on thermohaline circulation (McBean
et al., 1996).
The statistical analyses of the daily difference of temperature between maxima and
minima from 2000 stations all over the world for a period of 40 years show that nights are
warmer than days, 0.84~ and 0.28~ respectively. This means that the principal warming
is due to the increase of night temperatures. Statistics reveal that cloud cover seems to be
the cause of this circumstance (Henderson-Sellers, 1992), because clouds regulate night
temperatures by controlling long-wave emissions. During the 20th century, clouds have
increased 3.4 to 9.4%, possibly because of the increment of condensation nucleus due to air
pollution. This could explain the smaller percentage of clouds above oceans with respect
to continents. Without doubt, it is necessary to know the variations of cloud cover in order
to carry out further analysis of climate change in the future.
Volcanic activity, mainly in the case of acid composition eruptions, which are more
explosive, can occur sporadically and has a marked influence on climate. If the eruption
is large, volcanic ash is driven into the stratosphere, affecting general atmospheric circulation. In June 1991, the Pinatubo volcano, located in the Philippine islands, erupted.
Volcanic aerosols extended all over the planet and the models developed indicated that the
average global temperature decreased on the surface up to 0.5~ for 2 years and 0.6~ in
the troposphere for several months. The effects of the eruption were less evident in 1994.
The consequences of the volcanic activity, which produced opacity in the stratosphere, had
a significant influence on climate, but only sporadically.
Man, by means of industrial activity and agriculture, increases atmospheric dust
significantly. Also, large quantities of aeolian dust can be deposited on to continents and
into oceans from long distances. Dust reaches the upper part of the troposphere and restricts
solar radiation. As a result, there is a global cooling (Bryant, 1997).
The importance of anthropic sulphate aerosols on climate change is becoming
accepted. These aerosols come mainly from coal and petroleum combustion. Records
indicate that during the last century the exponential increase in sulphate aerosols is parallel
to the rise of CO2. The high reflectivity of the sulphate aerosols produces a cooling in the
troposphere with both clear and cloudy skies (Pearce, 1994; Santer et al., 1996).
Houghton et al. (1996) point out the difficulty for the prediction of long- and short-term
climate changes. This is what some authors call "climate surprises" (Jouzel and Lorius,
1999). Rapid climate variations have been found for the last glacial age. In cores obtained
from the Greenland icecap, several warming phases of about 10~ have been found. Those
phases lasted several tens of years and gradually turned into colder conditions. Such
sequences, the duration of which range from 500 to 2000 years, recurred about 20 times in
the last glacial epoch (Bender et al., 1994), and not only in Greenland. On the other hand,
Climatic Geomorphology
oceanic water, which constitutes an enormous reservoir of CO2, and marine biota play an
important role on the regulation dynamics of atmospheric CO2. Carbon dioxide flux in
the oceans depends on CO2 pressure, atmospheric concentration of CO2, and on surface
winds. Carbon dioxide pressure is controlled by oceanic transport processes, geochemical
processes, and biological processes in the top part of the oceans. Furthermore, solar flux
and latent calorific flow have an influence, as do the above-mentioned factors, in climate
modelling. Therefore, the system is very complex and the models of the flows in the
ocean-atmosphere inter-phase can be subject to large errors (Dickinson et al., 1996).
Moreover, there is limited knowledge on the temperature and salinity of deep waters, close
boundaries between currents, ocean eddies, and on thermohaline circulation (McBean
et al., 1996).
The statistical analyses of the daily difference of temperature between maxima and
minima from 2000 stations all over the world for a period of 40 years show that nights are
warmer than days, 0.84~ and 0.28~ respectively. This means that the principal warming
is due to the increase of night temperatures. Statistics reveal that cloud cover seems to be
the cause of this circumstance (Henderson-Sellers, 1992), because clouds regulate night
temperatures by controlling long-wave emissions. During the 20th century, clouds have
increased 3.4 to 9.4%, possibly because of the increment of condensation nucleus due to air
pollution. This could explain the smaller percentage of clouds above oceans with respect
to continents. Without doubt, it is necessary to know the variations of cloud cover in order
to carry out further analysis of climate change in the future.
Volcanic activity, mainly in the case of acid composition eruptions, which are more
explosive, can occur sporadically and has a marked influence on climate. If the eruption
is large, volcanic ash is driven into the stratosphere, affecting general atmospheric circulation. In June 1991, the Pinatubo volcano, located in the Philippine islands, erupted.
Volcanic aerosols extended all over the planet and the models developed indicated that the
average global temperature decreased on the surface up to 0.5~ for 2 years and 0.6~ in
the troposphere for several months. The effects of the eruption were less evident in 1994.
The consequences of the volcanic activity, which produced opacity in the stratosphere, had
a significant influence on climate, but only sporadically.
Man, by means of industrial activity and agriculture, increases atmospheric dust
significantly. Also, large quantities of aeolian dust can be deposited on to continents and
into oceans from long distances. Dust reaches the upper part of the troposphere and restricts
solar radiation. As a result, there is a global cooling (Bryant, 1997).
The importance of anthropic sulphate aerosols on climate change is becoming
accepted. These aerosols come mainly from coal and petroleum combustion. Records
indicate that during the last century the exponential increase in sulphate aerosols is parallel
to the rise of CO2. The high reflectivity of the sulphate aerosols produces a cooling in the
troposphere with both clear and cloudy skies (Pearce, 1994; Santer et al., 1996).
Houghton et al. (1996) point out the difficulty for the prediction of long- and short-term
climate changes. This is what some authors call "climate surprises" (Jouzel and Lorius,
1999). Rapid climate variations have been found for the last glacial age. In cores obtained
from the Greenland icecap, several warming phases of about 10~ have been found. Those
phases lasted several tens of years and gradually turned into colder conditions. Such
sequences, the duration of which range from 500 to 2000 years, recurred about 20 times in
the last glacial epoch (Bender et al., 1994), and not only in Greenland. On the other hand,