Anthropogenic
Contributions to Future Sea
Level and Temperature
Chase Asher
Critical Literature Review
Geo 387H 12/7/06
Outline
Introduction
Sea Level Change


Thermal Expansion
Glacial Melting
Temperature Change


Constant Composition
Constant Emission
Summary
Sources
Introduction
Intergovernmental Panel on Climate Change
released its Third Annual Report in 2001


This featured the ‘hockey stick’ diagram.
Helped to bring worldwide focus to the global
warming issue.
Several people questioned the veracity of the
claims of the TAR.


Some claims of overestimation.
Some models not applicable outside of a specific
purpose (Melt model)
Sea Level Change
Sea level change, even more than
temperature, affects people immediately.


Changing coastlines
Changing fisheries
In the long term, sea level can also affect
habitats

Epipelagic zone would be altered, causing
damage to existing coral reefs and other
delicate ecosystems.
Sea Level Change
Sea level rises through one of two
methods:

Thermal expansion.
The physical result of heating the water. Like all
matter, it expands when heated.

Melting ice.
Ice comes either from alpine glaciers, or ice sheets
such as those in Antarctica or Greenland.
Thermal Expansion
Small temperature changes (<1˚ C ) can
equate to sea level changes measured in
centimeters
This increase in sea level is unavoidable,
even if we were to stabilize atmospheric
CO2.
Two models discussed:


Parallel Climate Model
Community Climate System Model
Parallel Climate Model
Older and more established of the two
models.
Equilibrium climate sensitivity of 2.1˚ C
Transient Climate Response of 1.3˚ C
Coarser resolution over land.
Worse parameterizations, but corresponds
better with known data.
Does not include meltwater.
Community Climate System Model
Newer modeling system.
Equilibrium climate sensitivity of 2.1˚ C
Transient climate response of 1.3˚ C
Higher resolution.
Better parameterization.
Does not include meltwater.
Comparison
B1, A1B, and A2 are
differing levels of carbon
dioxide.
Even A1B would be a
difficult target without
reducing emissions to
what they were before the
nineties.
Even for the case where
CO2 stabilizes at 2000,
the globe warms by .4C
(PCM) or .6C (CCSM).
CCSM’s higher sensitivity
is clearly visible.
Comparison
Global average
temperature increases
more in the CCSM model
once again.
Temperature increase in
the North Atlantic
especially is due to a
decrease of meridional
overturning, which
causes a more defined
thermocline and
increased forcing.
Glacial Melting
Glaciers melting are
generally considered to
be the source of most of
the increase in sea level.
Though one paper
(Raper, 2006) disagrees
and gives thermal
expansion greater
importance.
In general, glacial
surfaces melt much faster
than ice sheets, due to an
increased surface area to
volume ratio.
Glacial Melting
IPCC TAR used a melt model which is
used in most studies with some
modifications.
Only takes into account glaciers and small
ice caps (GSIC).
There is an empirical limitation which puts
an artificial ceiling on melting after 2100.
Corrected TAR formula
The corrected TAR
formula created by
Wigley and Raper solves
this problem.
Matches up well with
original TAR formula
before 2100.
Continues on realistically
afterwards, tending
asymptotically to the
initially available ice
volume.
Results of New Model
Three different CO2
situations are shown in
these graphs, as well as
different mass balance
sensitivities.
Even after CO2
concentration stabilizes,
radiative forcing
continues to increase
due to climate inertia.
Glacier vs Ice Cap Melting
Raper claimed that it
was not ice caps that
were contributing to
the rising sea level
most, but glaciers.
For three different
initial volumes of
glacial ice, glacial
outpaced ice cap
water for the next 600
years.
Temperature Change
Two Different Models

Constant Composition
Assumes that no further green house gasses were
put into the atmosphere after 2000.
An impossible model and extreme baseline
prediction.

Constant Emission
Assumes that emission rates for GHG’s remain
constant at 2000 levels.
A more realistic view of temperature change.
Constant Composition
Even with constant
composition, the climate is still
catching up to its equilibrium
warming commitment of .5 ˚ C.
Following traditional physics it
would never actually reach this
equilibrium.
Wigley creates a time
dependent model, so the
climate approaches it
asymptotically.
Climate sensitivity and aerosol
forcing both affect the end
result to an appreciable
degree.
Constant Emission
Increase in
temperature is much
more dramatic with
increasing equilibrium
temperature.
Aerosol forcing is
much weaker
compared to climate
sensitivity.
Less asymptotic,
more linear.
Conclusions
Anthropogenic forcing is almost certainly
altering the climate.
The degree to which it is altering the
climate is difficult to determine.
Altering current emissions practices could
have far reaching benefits, but fewer
immediate ones.
No one estimate for sea level rise or
temperature is good on its own.
Thank you!
Sources
Literature Sources:
1.
Meehl , Gerald A et al. (2004)How Much More Global Warming and Sea Level
Rise? Science, Vol 307, page 1769-1772.
2.
Wigley, T.M.L.. (2004) The Climate Change Commitment. Science, Vol 307,
page 1766-1769.
3.
Kohfeld, Karen E. et al. (2004) Role of Marine Biology in Glacial-Interglacial
CO2 Cycles. Science, Vol 308, page 74-78.
4.
Wigley, T. M. L. and Raper, S. C. B. (2004) Extended scenarios for glacier melt
due to anthropogenic forcing. Geophysical Research Letters, Vol 32, L05704,
doi:10.1029/2004GL021238, 2005.
5.
Hansen, James (2005) A slippery slope: How much global warming constitutes
“Dangerous anthropogenic interference”? Climactic Change, Vol 68, 269-279.
6.
Koch, Dorothy and Hansen, James Distant origins of Arctic black carbon: A
Goddard
Institute for Space Studies ModelE experiment. JOURNAL OF GEOPHYSICAL
RESEARCH, VOL. 110, D04204, doi:10.1029/2004JD005296, 2005
7.
Raper, S.C.B. and Braithwaite, Roger J. Low sea level rise projections from
mountain
glaciers and icecaps under global warming. Letters, Vol 439, 19 January 2006,
doi:10.1038/nature04448