444
Hjalmar THIEL
will allow the impacts to be predicted confidently,
and such experiments must be conducted on a scale
from which the results can be extrapolated to fullscale disposal actions. For mud dumping a set of
integrated disposal experiments of increasing size has
been proposed (Thiel et al., 1998). A large amount
of mud, still small compared with an economically
viable operation, should be deposited at a suitable
site, already well studied in a baseline survey. Apart
from topographical, biological and sedimentological
descriptions, the current system must be analysed for
at least one year, including measurements close to
the seafloor and records of possible resuspension of
sediment. After dumping, careful monitoring of the effects on the environment should include visual controls
using a submersible or at least a remotely operated
vehicle. If this step and its extrapolation to larger scales
seem to be acceptable, a test disposal probably ten
times larger should be arranged for, followed by an
even larger one. Assuming an expected disposal of
10
6 m
3 per year, the experimental design for the steps
could cover 10
5 m
3 , 10
6 m
3 and in the pilot disposal
operation (PDO) 10
6 m
3 for ten subsequent years.
Careful monitoring of all effects must be conducted
between the steps, with high technical and personal
dedication. For financial reasons, such a test could
be conducted only in cooperation with an industrial
enterprise, and this would demand exact planning and
implementation, with carefully chosen time schedules
for the disposal and monitoring periods.
Carbon dioxide
One of the options to reduce atmospheric carbon
dioxide (CO 2 ) is its storage in the deep sea (Ormerod
and Angel, 1996). Carbon dioxide is well known as
a “greenhouse gas” produced by society in excess of
natural equilibrium. The content of carbon dioxide in
the atmosphere has increased by about 50% during the
last 200 years. Although technical and political efforts
are being made to mitigate the emission of carbon
dioxide, industrialization of “third-world” countries
and increases in world population will probably cause
the atmospheric concentration to double during the
next century. All effective methods must therefore
be mobilized against this development and related
anthropogenic climate changes. Reductions of carbon
dioxide production are still more than counterbalanced
by enhanced energy consumption for the purpose of
increasing food production (Pimentel et al., 1994). In
order to increase agricultural areas deforestation will be
called for, thus reducing the terrestrial uptake of carbon
dioxide and, consequently increasing the atmospheric
carbon dioxide (Keller et al., 1996). More energy
will be demanded by expanding industry. Powerplants burning pulverized coal produce 23 kg of carbon
dioxide per second to generate 100 megawatts; this
output of carbon dioxide is equivalent to 7×10
5 tonnes
of carbon per year. It is generally accepted that the
increase in atmospheric carbon dioxide will cause
a change in global radiation balance, even if some
doubt is expressed about its influence on climate
development. It may be difficult to counterbalance this
change in radiation, but its global environmental and
socio-economic implications may be so destructive that
all possible measures must be taken to limit it. The
situation is serious and requires urgent discussions
and precautionary research on the various options to
mitigate increase in atmospheric carbon dioxide and its
potential impacts on the global ecosystem.
Whereas the avoidance of production of carbon
dioxide and its release into the atmosphere should have
priority in all developments, the gas may be discharged
into geological formations deep below the seafloor,
including saline aquifers, coal beds that cannot be
mined, depleted oil and gas reservoirs, rock caverns,
and mined salt domes in many localities of the world
(Herzog et al., 2000). This is already happening, for
instance, in the Sleipner oil and gas field 240 km off
the Norwegian coast. In other situations sequestration
in the deep ocean may be the best practical option.
Certainly this would short-cut the natural passage of
carbon dioxide from the atmosphere and the ocean
surface into the deep sea by physical and biological
processes, and later back to the surface, which may take
many hundreds to thousands of years. Carbon dioxide
pumped into the deep ocean may return to the surface
and the atmosphere after 500 years; but this would
be a long delay, and by that time one may hope that
succeeding human generations will have found ways to
reduce carbon dioxide emission greatly, or to dispose of
it in other ways. There is little time left either for the
present or for future generations.
Several options exist for the disposal of carbon
dioxide into the oceans (Ohsumi, 1996). They are
related to the thermophysical phases of this compound
(Uchida et al., 1995), depending on temperature and on
pressure, given as water depth:
– gaseous: surface – ~500 m;
– liquid: >~500 m, >11ºC;
– solid and gaseous: ~130–~350 m, <11ºC;
Hjalmar THIEL
will allow the impacts to be predicted confidently,
and such experiments must be conducted on a scale
from which the results can be extrapolated to fullscale disposal actions. For mud dumping a set of
integrated disposal experiments of increasing size has
been proposed (Thiel et al., 1998). A large amount
of mud, still small compared with an economically
viable operation, should be deposited at a suitable
site, already well studied in a baseline survey. Apart
from topographical, biological and sedimentological
descriptions, the current system must be analysed for
at least one year, including measurements close to
the seafloor and records of possible resuspension of
sediment. After dumping, careful monitoring of the effects on the environment should include visual controls
using a submersible or at least a remotely operated
vehicle. If this step and its extrapolation to larger scales
seem to be acceptable, a test disposal probably ten
times larger should be arranged for, followed by an
even larger one. Assuming an expected disposal of
10
6 m
3 per year, the experimental design for the steps
could cover 10
5 m
3 , 10
6 m
3 and in the pilot disposal
operation (PDO) 10
6 m
3 for ten subsequent years.
Careful monitoring of all effects must be conducted
between the steps, with high technical and personal
dedication. For financial reasons, such a test could
be conducted only in cooperation with an industrial
enterprise, and this would demand exact planning and
implementation, with carefully chosen time schedules
for the disposal and monitoring periods.
Carbon dioxide
One of the options to reduce atmospheric carbon
dioxide (CO 2 ) is its storage in the deep sea (Ormerod
and Angel, 1996). Carbon dioxide is well known as
a “greenhouse gas” produced by society in excess of
natural equilibrium. The content of carbon dioxide in
the atmosphere has increased by about 50% during the
last 200 years. Although technical and political efforts
are being made to mitigate the emission of carbon
dioxide, industrialization of “third-world” countries
and increases in world population will probably cause
the atmospheric concentration to double during the
next century. All effective methods must therefore
be mobilized against this development and related
anthropogenic climate changes. Reductions of carbon
dioxide production are still more than counterbalanced
by enhanced energy consumption for the purpose of
increasing food production (Pimentel et al., 1994). In
order to increase agricultural areas deforestation will be
called for, thus reducing the terrestrial uptake of carbon
dioxide and, consequently increasing the atmospheric
carbon dioxide (Keller et al., 1996). More energy
will be demanded by expanding industry. Powerplants burning pulverized coal produce 23 kg of carbon
dioxide per second to generate 100 megawatts; this
output of carbon dioxide is equivalent to 7×10
5 tonnes
of carbon per year. It is generally accepted that the
increase in atmospheric carbon dioxide will cause
a change in global radiation balance, even if some
doubt is expressed about its influence on climate
development. It may be difficult to counterbalance this
change in radiation, but its global environmental and
socio-economic implications may be so destructive that
all possible measures must be taken to limit it. The
situation is serious and requires urgent discussions
and precautionary research on the various options to
mitigate increase in atmospheric carbon dioxide and its
potential impacts on the global ecosystem.
Whereas the avoidance of production of carbon
dioxide and its release into the atmosphere should have
priority in all developments, the gas may be discharged
into geological formations deep below the seafloor,
including saline aquifers, coal beds that cannot be
mined, depleted oil and gas reservoirs, rock caverns,
and mined salt domes in many localities of the world
(Herzog et al., 2000). This is already happening, for
instance, in the Sleipner oil and gas field 240 km off
the Norwegian coast. In other situations sequestration
in the deep ocean may be the best practical option.
Certainly this would short-cut the natural passage of
carbon dioxide from the atmosphere and the ocean
surface into the deep sea by physical and biological
processes, and later back to the surface, which may take
many hundreds to thousands of years. Carbon dioxide
pumped into the deep ocean may return to the surface
and the atmosphere after 500 years; but this would
be a long delay, and by that time one may hope that
succeeding human generations will have found ways to
reduce carbon dioxide emission greatly, or to dispose of
it in other ways. There is little time left either for the
present or for future generations.
Several options exist for the disposal of carbon
dioxide into the oceans (Ohsumi, 1996). They are
related to the thermophysical phases of this compound
(Uchida et al., 1995), depending on temperature and on
pressure, given as water depth:
– gaseous: surface – ~500 m;
– liquid: >~500 m, >11ºC;
– solid and gaseous: ~130–~350 m, <11ºC;