Understanding and Projecting Sea Level Change: An Overview of the IPCC 5th Assessment Report (AR5)
R. Steven
Nerem On Behalf of the Working Group I Chapter 13 Writing Team
University of Colorado at Boulder
Keynote
John A. Church (Australia), Peter U. Clark (USA), Anny Cazenave (France),
Jonathan M. Gregory (UK), Svetlana Jevrejeva (UK), Anders Levermann (Germany),
Mark A. Merrifield (USA), Glenn A. Milne (Canada), R. Steven Nerem (USA),
Patrick D. Nunn (Australia), Antony J. Payne (UK), W. Tad Pfeffer (USA),
Detlef Stammer (Germany), Alakkat S. Unnikrishnan (India)
The rate of global mean sea level rise (GMSLR) has accelerated during the last
two centuries, from a rate of order tenths of mm/yr during the late
Holocene, to about 1.7 mm/yr since 1901. Ocean thermal expansion and
glacier melting were the dominant contributors to 20th century GMSLR, with
relatively small contributions from the Greenland and Antarctic ice sheets.
Process-based models suggest that the larger rate of rise since 1990 results
from increased radiative forcing (both natural and anthropogenic) and
increased ice-sheet outflow, induced by warming of the immediately adjacent
ocean. Confidence in projections of global mean sea level rise has increased
since the AR4 because of improved physical process-based understanding of
observed sea level change, especially in recent decades, and the inclusion of
future rapid ice-sheet dynamical changes, for which a quantitative assessment
could not be made on the basis of scientific knowledge available at the time
of the AR4. By 2100, the rate of GMSLR for a scenario of high emissions
(RCP8.5) could approach the average rates that occurred during the last
deglaciation, whereas for a strong emissions mitigation scenario (RCP2.6) it
could stabilize at rates similar to those of the early 21st century. In either
case, GMSLR will continue for many subsequent centuries. Although there has
been much recent progress, projections of ice-sheet change are still
uncertain, especially beyond 2100. Future sea level change will not be
globally uniform, but models still exhibit substantial disagreement in
projections of ice mass loss and ocean dynamics, which are the main influences
on the pattern. Uncertainty in projections of future storminess is a further
obstacle to confident projection of changes in sea level extremes.
Jonathan M. Gregory (UK), Svetlana Jevrejeva (UK), Anders Levermann (Germany),
Mark A. Merrifield (USA), Glenn A. Milne (Canada), R. Steven Nerem (USA),
Patrick D. Nunn (Australia), Antony J. Payne (UK), W. Tad Pfeffer (USA),
Detlef Stammer (Germany), Alakkat S. Unnikrishnan (India)
The rate of global mean sea level rise (GMSLR) has accelerated during the last
two centuries, from a rate of order tenths of mm/yr during the late
Holocene, to about 1.7 mm/yr since 1901. Ocean thermal expansion and
glacier melting were the dominant contributors to 20th century GMSLR, with
relatively small contributions from the Greenland and Antarctic ice sheets.
Process-based models suggest that the larger rate of rise since 1990 results
from increased radiative forcing (both natural and anthropogenic) and
increased ice-sheet outflow, induced by warming of the immediately adjacent
ocean. Confidence in projections of global mean sea level rise has increased
since the AR4 because of improved physical process-based understanding of
observed sea level change, especially in recent decades, and the inclusion of
future rapid ice-sheet dynamical changes, for which a quantitative assessment
could not be made on the basis of scientific knowledge available at the time
of the AR4. By 2100, the rate of GMSLR for a scenario of high emissions
(RCP8.5) could approach the average rates that occurred during the last
deglaciation, whereas for a strong emissions mitigation scenario (RCP2.6) it
could stabilize at rates similar to those of the early 21st century. In either
case, GMSLR will continue for many subsequent centuries. Although there has
been much recent progress, projections of ice-sheet change are still
uncertain, especially beyond 2100. Future sea level change will not be
globally uniform, but models still exhibit substantial disagreement in
projections of ice mass loss and ocean dynamics, which are the main influences
on the pattern. Uncertainty in projections of future storminess is a further
obstacle to confident projection of changes in sea level extremes.
OSTS session
Science Results from Satellite Altimetry