will depend strongly on the warming pattern of
the ocean.
The ocean water contains about 50 times the
carbon stored in the atmosphere. On average about
90 billion tons of carbon (GtC) are released from
the ocean and about 92 GtC are absorbed by the
ocean each year. Carbon models indicate a net
uptake of 2<0.8 GtC released from anthropogenic
sources during the 1980s. Colleagues from the Joint
Global Ocean Flux Study (JGOFS) used the WOCE
Hydrographic Programme to collect a global ocean
carbon data set, which is being used to improve our
understanding of the carbon cycle within the ocean
(Wallace, Chapter 6.3). JGOFS process studies have
examined how different marine ecosystems take up
carbon in different parts of the oceans from the
tropics to the poles. Changes in the temperature,
vertical stability, circulation and marine ecosystems
will change how and where the ocean will take
up carbon in the future (Sarmiento et al., 1998;
Matear and Hirst, 1999). Ocean colour satellite
systems offer a way to monitor the biological component of this carbon uptake into the future. It will
be important to include ocean carbon chemistry
and biology in future ocean climate models.
Mean sea-level rise is one of the major consequences of anthropogenic climate change. While
the further melting of land ice (glaciers, small ice
caps, ice sheets) will certainly lead to sea-level rise,
thermal expansion of seawater will be the dominant contribution during the twenty-first century
(Clarke et al., Chapter 1.2). Model calculations
indicate sea-level rise will have large regional variations but as yet there is little confidence in these
regional patterns (Clarke et al., Chapter 1.2). Sealevel rise threatens the coastal zone where most of
the world population lives, especially those zones
where there may be concomitant increases in
storm surges. Thus, sea-level rise is a major argument in the political debates on anthropogenic
climate change. Here again, WOCE has led to a
breakthrough by the advent of precise altimeter
measurements of local, regional and global sea level
(Fu, Chapter 3.3) and observations of ocean warming and thus thermal expansion (Church et al.,
2001). If altimeters on TOPEX/POSEIDON are
continued on Jason, we will soon have more than a
decade of precise global sea-level observations
from space that – if calibrated by reliable coastal
tide gauges – will remove the large uncertainties
associated with present estimates of sea-level rise.
Although the contribution of the melting ice
from mountain glaciers, small ice caps and ice
sheets to sea-level changes can only be roughly
estimated because of the lack of sufficiently
accurate mass budgets for most glaciers, present
understanding of sea-level rise does not point to
potential major surprises. Furthermore, the long
debate on the instability of the West Antarctic Ice
Sheet has recently been less intense, but there is
still no firm conclusion. As stated in Warrick et al.
(1996, p. 389): ‘Estimating the likelihood of a collapse during the next century is not yet possible. If
collapse occurs it will probably be caused more by
climate changes of the last 10 000 years rather than
greenhouse induced warming. Nonetheless, such a
collapse, once initiated, would be irreversible.’
1.1.7 Future climate research and ocean
observing systems
WOCE has revealed large-scale patterns of decadal
change in the ocean whereas previously there was a
tacit assumption of a steady-state ocean. It is also
revealing significant horizontal and vertical variations in small-scale mixing compared with the
uniform pattern assumed in earlier climate models.
Thus, WOCE’s Analysis Interpretation Modelling
and Synthesis (AIMS) phase is in a more challenging position than anticipated at the conception of
WOCE. Will it be possible to get a consistent picture of ocean structure and circulation if one only
has – taking a comparison to a meteorological case –
a few radiosonde ascents at different times over
different continents? A partial answer is already
given in the new projects that WOCE and TOGA
have stimulated: CLIVAR and GODAE. These programmes will build on the understanding gained
and the techniques developed through the assimilation of the WOCE data set into global ocean
models (Talley et al., Chapter 7.1). While significant progress has been made, much remains to be
done and continued observations are essential.
Ocean observations are more difficult to obtain
than atmospheric observations because the ocean
is virtually opaque to electromagnetic radiation.
Remote sensing from space is thus restricted to
the ocean surface and the upper parts of the
euphotic zone for visible radiation. Thus, the full
understanding of decadal time scale climate variability requires – as mentioned earlier – sustained
observation in the ocean on a full global scale.
SECTION 1 THE OCEAN AND CLIMATE
8
the ocean.
The ocean water contains about 50 times the
carbon stored in the atmosphere. On average about
90 billion tons of carbon (GtC) are released from
the ocean and about 92 GtC are absorbed by the
ocean each year. Carbon models indicate a net
uptake of 2<0.8 GtC released from anthropogenic
sources during the 1980s. Colleagues from the Joint
Global Ocean Flux Study (JGOFS) used the WOCE
Hydrographic Programme to collect a global ocean
carbon data set, which is being used to improve our
understanding of the carbon cycle within the ocean
(Wallace, Chapter 6.3). JGOFS process studies have
examined how different marine ecosystems take up
carbon in different parts of the oceans from the
tropics to the poles. Changes in the temperature,
vertical stability, circulation and marine ecosystems
will change how and where the ocean will take
up carbon in the future (Sarmiento et al., 1998;
Matear and Hirst, 1999). Ocean colour satellite
systems offer a way to monitor the biological component of this carbon uptake into the future. It will
be important to include ocean carbon chemistry
and biology in future ocean climate models.
Mean sea-level rise is one of the major consequences of anthropogenic climate change. While
the further melting of land ice (glaciers, small ice
caps, ice sheets) will certainly lead to sea-level rise,
thermal expansion of seawater will be the dominant contribution during the twenty-first century
(Clarke et al., Chapter 1.2). Model calculations
indicate sea-level rise will have large regional variations but as yet there is little confidence in these
regional patterns (Clarke et al., Chapter 1.2). Sealevel rise threatens the coastal zone where most of
the world population lives, especially those zones
where there may be concomitant increases in
storm surges. Thus, sea-level rise is a major argument in the political debates on anthropogenic
climate change. Here again, WOCE has led to a
breakthrough by the advent of precise altimeter
measurements of local, regional and global sea level
(Fu, Chapter 3.3) and observations of ocean warming and thus thermal expansion (Church et al.,
2001). If altimeters on TOPEX/POSEIDON are
continued on Jason, we will soon have more than a
decade of precise global sea-level observations
from space that – if calibrated by reliable coastal
tide gauges – will remove the large uncertainties
associated with present estimates of sea-level rise.
Although the contribution of the melting ice
from mountain glaciers, small ice caps and ice
sheets to sea-level changes can only be roughly
estimated because of the lack of sufficiently
accurate mass budgets for most glaciers, present
understanding of sea-level rise does not point to
potential major surprises. Furthermore, the long
debate on the instability of the West Antarctic Ice
Sheet has recently been less intense, but there is
still no firm conclusion. As stated in Warrick et al.
(1996, p. 389): ‘Estimating the likelihood of a collapse during the next century is not yet possible. If
collapse occurs it will probably be caused more by
climate changes of the last 10 000 years rather than
greenhouse induced warming. Nonetheless, such a
collapse, once initiated, would be irreversible.’
1.1.7 Future climate research and ocean
observing systems
WOCE has revealed large-scale patterns of decadal
change in the ocean whereas previously there was a
tacit assumption of a steady-state ocean. It is also
revealing significant horizontal and vertical variations in small-scale mixing compared with the
uniform pattern assumed in earlier climate models.
Thus, WOCE’s Analysis Interpretation Modelling
and Synthesis (AIMS) phase is in a more challenging position than anticipated at the conception of
WOCE. Will it be possible to get a consistent picture of ocean structure and circulation if one only
has – taking a comparison to a meteorological case –
a few radiosonde ascents at different times over
different continents? A partial answer is already
given in the new projects that WOCE and TOGA
have stimulated: CLIVAR and GODAE. These programmes will build on the understanding gained
and the techniques developed through the assimilation of the WOCE data set into global ocean
models (Talley et al., Chapter 7.1). While significant progress has been made, much remains to be
done and continued observations are essential.
Ocean observations are more difficult to obtain
than atmospheric observations because the ocean
is virtually opaque to electromagnetic radiation.
Remote sensing from space is thus restricted to
the ocean surface and the upper parts of the
euphotic zone for visible radiation. Thus, the full
understanding of decadal time scale climate variability requires – as mentioned earlier – sustained
observation in the ocean on a full global scale.
SECTION 1 THE OCEAN AND CLIMATE
8