catastrophic impacts. Current thinking is that collapse is unlikely during the
21st century. For instance, Vaughan and Sponge concluded that the probability
of a sea-level rise contribution from the WAIS of more than 0.5 m during the 21st
century was 5%. Going beyond 2100, this probability increases. Thus, WAIS
collapse remains a plausible, albeit unlikely scenario, and from an impacts
perspective it should not be totally discounted, particularly if changes over 100;
years are being considered.
The SRES emission scenarios have a wide divergence, reflecting the different
storylines that are considered plausible. In addition, mitigation (or deliberate
reduction) of greenhouse gas emissions could be implemented with the Kyoto
Protocol being the beginning of this process. However, even if atmospheric
greenhouse-gas concentrations are stabilized in the next few decades, a rise in
global-mean sea level still follows. This has been termed ‘the commitment to
sea-level rise’, which reflects the slow penetration of heat into the deeper ocean: it
may take thousands of years to reach equilibrium with the new conditions.
Subsequent analyses suggest that global-mean sea-level rise is almost independent
of future emissions to 2050, and future emissions become most important in
controlling sea-level rise after 2100. During the 21st century, the main source
of uncertainty concerning global-mean sea-level rise is the climate response to the
emissions, particularly the climate sensitivity. Therefore, some global-mean
sea-level rise appears inevitable during the 21st century and beyond, even given
substantial mitigation of climate change. (Note the important point that
mitigation also makes abrupt climate change events such as the WAIS collapse
even more unlikely. This benefit of mitigation is almost always ignored.)
An example of relative sea-level observations and a high, mid and low scenario
based on the scenarios of Church et al. are shown for New York City in Figure 3.
The rise during the 20th century (30 cm/century) is 10—20 cm/century larger than
the global-mean trend, reflecting the fact that New York is slowly subsiding due
to GIA. The relative mid scenario shows a 2-fold acceleration relative to the
20th century. However, the range is more than a 3-fold acceleration to a slight
deceleration. Note that the scenarios assume no meteo-oceanographic effects at
New York, but they do take account of the uncertainty in subsidence. All these
uncertainties need to be considered when assessing responses to sea-level rise (see
later).
S. H. Schneider and R. S. Chen, Carbon dioxide flooding: physical factors and climatic impact,
Annu. Rev. Energy, 1980, 5, 107—140.
Referenced in J. A. Church, J. M. Gregory, P. Huybrechts, M. Kuhn, K. Lambeck, M. T. Nhuan, D.
Qin and P. L. Woodworth, Changes in sea level, in J. T. Houghton, Y. Ding, D. J. Griggs, M.
Noguer, P. J. van der Linden and D. Xiaosu (eds.), Climate Change 2001. The Scientific Basis,
Cambridge University Press, Cambridge, 2001, pp. 639—693.
T. M. L Wigley and S. C. B. Raper, Future changes in global mean temperature and sea level, in
R. A. Warrick, E. M. Barrow and T. M. L. Wigley (eds.), Climate and Sea Level Change:
Observation, Projections and Implications, Cambridge University Press, Cambridge, 1993, pp. 111—133.
T. M. L. Wigley, The Science of Climate Change: Global and U.S. Perspectives, Report for the Pew
Center on Global Climate Change, Arlington, VA, 1999, 51 pp. (http://www.pewclimate.org/projects/env—science.cfm)
B. C. Douglas, Global sea-level rise. J. Geophys. Res., 1991, 96 (C4), 6981—6992.
R. J. Nicholls
88
21st century. For instance, Vaughan and Sponge concluded that the probability
of a sea-level rise contribution from the WAIS of more than 0.5 m during the 21st
century was 5%. Going beyond 2100, this probability increases. Thus, WAIS
collapse remains a plausible, albeit unlikely scenario, and from an impacts
perspective it should not be totally discounted, particularly if changes over 100;
years are being considered.
The SRES emission scenarios have a wide divergence, reflecting the different
storylines that are considered plausible. In addition, mitigation (or deliberate
reduction) of greenhouse gas emissions could be implemented with the Kyoto
Protocol being the beginning of this process. However, even if atmospheric
greenhouse-gas concentrations are stabilized in the next few decades, a rise in
global-mean sea level still follows. This has been termed ‘the commitment to
sea-level rise’, which reflects the slow penetration of heat into the deeper ocean: it
may take thousands of years to reach equilibrium with the new conditions.
Subsequent analyses suggest that global-mean sea-level rise is almost independent
of future emissions to 2050, and future emissions become most important in
controlling sea-level rise after 2100. During the 21st century, the main source
of uncertainty concerning global-mean sea-level rise is the climate response to the
emissions, particularly the climate sensitivity. Therefore, some global-mean
sea-level rise appears inevitable during the 21st century and beyond, even given
substantial mitigation of climate change. (Note the important point that
mitigation also makes abrupt climate change events such as the WAIS collapse
even more unlikely. This benefit of mitigation is almost always ignored.)
An example of relative sea-level observations and a high, mid and low scenario
based on the scenarios of Church et al. are shown for New York City in Figure 3.
The rise during the 20th century (30 cm/century) is 10—20 cm/century larger than
the global-mean trend, reflecting the fact that New York is slowly subsiding due
to GIA. The relative mid scenario shows a 2-fold acceleration relative to the
20th century. However, the range is more than a 3-fold acceleration to a slight
deceleration. Note that the scenarios assume no meteo-oceanographic effects at
New York, but they do take account of the uncertainty in subsidence. All these
uncertainties need to be considered when assessing responses to sea-level rise (see
later).
S. H. Schneider and R. S. Chen, Carbon dioxide flooding: physical factors and climatic impact,
Annu. Rev. Energy, 1980, 5, 107—140.
Referenced in J. A. Church, J. M. Gregory, P. Huybrechts, M. Kuhn, K. Lambeck, M. T. Nhuan, D.
Qin and P. L. Woodworth, Changes in sea level, in J. T. Houghton, Y. Ding, D. J. Griggs, M.
Noguer, P. J. van der Linden and D. Xiaosu (eds.), Climate Change 2001. The Scientific Basis,
Cambridge University Press, Cambridge, 2001, pp. 639—693.
T. M. L Wigley and S. C. B. Raper, Future changes in global mean temperature and sea level, in
R. A. Warrick, E. M. Barrow and T. M. L. Wigley (eds.), Climate and Sea Level Change:
Observation, Projections and Implications, Cambridge University Press, Cambridge, 1993, pp. 111—133.
T. M. L. Wigley, The Science of Climate Change: Global and U.S. Perspectives, Report for the Pew
Center on Global Climate Change, Arlington, VA, 1999, 51 pp. (http://www.pewclimate.org/projects/env—science.cfm)
B. C. Douglas, Global sea-level rise. J. Geophys. Res., 1991, 96 (C4), 6981—6992.
R. J. Nicholls
88