A few thoughts on IPCC AR4 and ice:

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• A few thoughts on IPCC AR4 and ice
• Ice occupies an anomalously prominent role in
  public discussions of climate change, so quality
  and continuity of observational record are
  important
• For seasonally and regionally resolved
  temperature projections, sea-ice change probably
  produces the largest signals, and the largest
  uncertainties
• AR4 highlighted carbon-cycle feedback as a main
  uncertainty, which is tied tightly to permafrost
  behavior (frozen carbon typically doesnt burn)
  
• AR4 neither a best estimate nor an upper limit on
  sea-level rise because of ice-sheet
  uncertainties may be the largest policy-relevant
  failure identified by the IPCC.

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Fig. 4.9 Arctic summer sea ice
Fig. 4.2 Northern snow cover
Fig. 4.18 Greenland ice sheet
Fig. 4.15b, Glaciers
Fig. 4.18 Antarctic ice sheet
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Warming of the climate system is unequivocal, as
is now evident from observations of increases in
global average air and ocean temperatures,
widespread melting of snow and ice, and rising
global average sea level (see Figure SPM-3).
3.2, 4.2, 5.5
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• There are worries concerning observational
  continuity
• GLAS (laser altimetry) is burning out
• GRACE (satellite gravity) is past design life
• InSAR suffers data-availability difficulties
• Visible imagery (LANDSAT) highly shaky
• Etc.
• And real issues with ground-truth (permafrost,
  snow courses, glacier and ice-sheet changes, etc.)

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improvement in simulating sea ice in these
models, as a group, is not obvious Even in the
best case (NH winter), the range of simulated sea
ice extent exceeds 50 of the mean, and ice
thickness also varies considerably, suggesting
that projected decreases in sea ice cover remain
rather uncertain. The model sea ice biases may
influence global climate sensitivity (see Section
8.6). There is a tendency for models with
relatively large sea ice extent in the present
climate to have higher sensitivity. (ch. 8, p.
616, IPCC WG1 AR4)
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Figure 8.10. Baseline climate (19801999) sea ice
distribution in the Northern Hemisphere (upper
panels) and Southern Hemisphere (lower panels)
simulated by 14 of the AOGCMs listed in Table 8.1
for March (left) and September (right), adapted
from Arzel et al. (2006). For each 2.5 x 2.5
longitude-latitude grid cell, the
figure indicates the number of models that
simulate at least 15 of the area covered by sea
ice. The observed 15 concentration boundaries
(red line) are based on the Hadley Centre Sea Ice
and Sea Surface Temperature (HadISST Rayner et
al., 2003) data set.
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Models used to date do not include uncertainties
in climate-carbon cycle feedback nor do they
include the full effects of changes in ice sheet
flow, because a basis in published literature is
lacking. The projections include a contribution
due to increased ice flow from Greenland and
Antarctica at the rates observed for 1993-2003,
but these flow rates could increase or decrease
in the future. For example, if this contribution
were to grow linearly with global average
temperature change, the upper ranges of sea level
rise for SRES scenarios shown in Table SPM-3
would increase by 0.1 m to 0.2 m. Larger values
cannot be excluded, but understanding of these
effects is too limited to assess their likelihood
or provide a best estimate or an upper bound for
sea level rise. 10.6 p. 14-15
8
Model-based projections of global average sea
level rise at the end of the 21st century
(2090-2099) are shown in Table SPM-3. For each
scenario, the midpoint of the range in Table
SPM-3 is within 10 of the TAR model average for
2090-2099. The ranges are narrower than in the
TAR mainly because of improved information about
some uncertainties in the projected
contributions15. 10.6 15 TAR projections were
made for 2100, whereas projections in this Report
are for 2090-2099. The TAR would have had similar
ranges to those in Table SPM-2 if it had treated
the uncertainties in the same way. p. 15
9
Alley et al., in press, Ann. Glac.
10
Alley et al., in press, Ann. Glac.
11
Alley et al., in press, Ann. Glac.
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Alley et al., in press, Ann. Glac.
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Models used to date do not includethe full
effects of changes in ice sheet flow, because a
basis in published literature is
lackingunderstanding of these effects is too
limited toprovide a best estimate or an upper
bound for sea level rise. 10.6
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Ice sheets have flying buttresses, too

• Floating extensions called ice shelves--ice
  flows over water for a while before breaking off
  to make bergs
• Ice shelves may run aground on islands or scrape
  past rocky sides of bays
• Friction from this slows ice-sheet spreading
• Warming air or water can attack ice shelves
  quickly, speeding ice-sheet spreading and
  sea-level rise.

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Antarctic Peninsula (gothic cathedral)
Ocean
12 mi
http//svs.gsfc.nasa.gov/vis/a000000/a002400/a0024
21/index.html
20 km
Melt ponds
Icebergs
Larsen B Ice Shelf (flying buttress)
January 31, 2002
16
12 mi
http//svs.gsfc.nasa.gov/vis/a000000/a002400/a0024
21/index.html
20 km
January 31, 2002
17
12 mi
20 km
http//svs.gsfc.nasa.gov/vis/a000000/a002400/a0024
21/index.html
March 7, 2002. 8x tributary flow-speed increase
followed
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Glaciers lost ice shelf
Ice Velocity December, 2003 October,
2003 December, 2002 BREAKUP FEB. 2002 October,
2000 January, 1996
Glacier lost ice shelf
Glacier still has ice shelf
Rignot et al., 2004, GRL
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• Thoughts on solutions
• The ice is big, the community small--there is
  plenty of room for capacity-building
• To me, the biggest shortcoming in our
  climate-change research effort is the failure to
  include ice sheets in the mission of the modeling
  centers
• Sensitivity studies (what data pay off best?)
• Data assimilation (still cant measure
  everything)
• Limiting cases (realistically, what is
  possible?)
• Serious model intercomparisons.

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CO2 in atmosphere has followed IPCC-linked
projections closely. Temperature rise has been a
bit larger than central projections, but well
within error bars. Sea-level rise has been well
above central projections, and barely within
error bars (sea-level-rise variability has been
high). Rahmstorf et al., Science, 2007