Arctic Sea Ice – Now and in the Future. J. Stroeve National Snow and Ice Data Center (NSIDC),...
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Transcript of Arctic Sea Ice – Now and in the Future. J. Stroeve National Snow and Ice Data Center (NSIDC),...
Arctic Sea Ice – Now and in the Future
Arctic Sea Ice – Now and in the FutureJ. StroeveNational Snow and Ice Data Center (NSIDC), Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado (CU)
With contributions from S. Drobot, M. Holland, R. Kwok, A. Mahoney, J. Maslanik, W. Meier, M. Serreze, J. Zwally
Arctic Sea Ice – Now and in the Future
The Poster Child of Climate Change: Arctic Sea Ice
Variability of September Sea Ice Cover (1979-2007)
Arctic Sea Ice – Now and in the Future
2005 Median September Ice Extent
1979-2000 Median September Ice Extent
1953-2000 Median September Ice Extent
Ice Loss in 2007 Extended Further Into Central Arctic
Arctic Sea Ice – Now and in the Future
Transition Towards Younger Ice
• Ice age tracking algorithm from C. Fowler and J. Maslanik show ice 5 years or older now only makes up 10% of the perennial ice pack.
Spring 1986 Spring 1990 Spring 2007
Maslanik et al., 2007
Arctic Sea Ice – Now and in the Future
Younger Ice is Thinner Ice
• Comparison between ice age and ice thickness from 4 years of spring ICESat GLAS-derived thickness fields from J. Zwally and D. Yi.
• Results suggest a decrease in mean thickness of 2.6 m in March 1987 to 2.0 m in March 2007
Maslanik et al., 2007
Arctic Sea Ice – Now and in the Future
Conditions this Spring: Ice Extent/Concentration
• Some recovery in winter extent, but still well-below normal
Source: nsidc.org/seaice_index
Arctic Sea Ice – Now and in the Future
Conditions for Spring 2008: Ice Age
First-year ice now covers 73% of the Arctic Basin, whereas in 2007 it covered 58%.
Data from C. Fowler and J. Maslanik
Arctic Sea Ice – Now and in the Future
Conditions for Spring 2008: Freeboard
Comparison between 2007 and 2008 suggests the seasonal ice cover is 5-10 cm thinner and covers more area in 2008
Image courtesy of R. Kwok
Arctic Sea Ice – Now and in the Future
Age as Proxy for Thickness and VolumeArctic Ice Volume (70-90N)
Week 11 (March)
15000
15500
16000
16500
17000
17500
18000
18500
19000
1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007
Year
Vo
lum
e (
km
^3
)
1987
1990
1995
1997
2000
2006
2007
2004
2008
Arctic Sea Ice – Now and in the Future
This Spring is Warm
April 2008 Air Temperature Anomalies (relative to 1979-2007)
Arctic Sea Ice – Now and in the Future
Survival of Winter Formed First Year IceSurvivability of Winter-Formed FYI
(Arctic Ocean Domain)
0
10
20
30
40
50
60
70
80
1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008
Year
FY
I Fra
ctio
n (
%)
wk11 FYI fraction
FYI at end of Melt Season
Arctic Sea Ice – Now and in the Future
Estimated 2008 Minimum Sea Ice Extent
• Based on survival rates from previous years (Drobot et al., GRL, submitted)
Estimated end-of-summer minimum sea ice extent for 2008 based on previous years' melt data
1996
1994
1992
1997
2001
2000
1989
1988
2004
1986
1991
1995
1987
1985
1998
1993
2006
1990
2002
1999
2003
2005
2007
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
Ext
ent
(mill
ion
sq
-km
)
2007 Record minimum extent: 4.13 mil. sq-km
Average estimate: 3.48 mil. sq-km
Arctic Sea Ice – Now and in the Future
Does 2007 Represent a Tipping Point?• Tipping Point – what is it?
A threshold at which the sea ice cover rapidly transitions to a new stable (seasonally ice-free) equilibrium state.
• Abrupt climate change is often defined in the context of this type of tipping point behavior (e.g. National Research Council, 2002).
• Some climate models suggest that a transition towards seasonally ice-free conditions may result from “tipping point” behavior (e.g. Winton, 2006).
• Other models suggest abrupt change may happen, but may not constitute a threshold response (e.g. CCSM3).
Arctic Sea Ice – Now and in the Future
Abrupt Ice Loss
• Climate models suggest that once the ice thins sufficiently, it becomes vulnerable to natural variability such that abrupt ice losses may occur (Holland et al., 2006).
0
1
2
3
4
5
6
7
8
9
10
1900 1920 1940 1960 1980 2000 2020 2040 2060 2080 2100
Year
Ice
Ex
ten
t (m
illi
on
sq
-k
m)
NCAR CCSM3 model simulationObservations
Model drop1.8 million sq km, 2024–2025
Observed drop1.6 million sq km, 2006–2007
September Sea Ice Extent
Arctic Sea Ice – Now and in the Future
The Set up Looks Right
• Mean thickness (70-90N) in CCSM3 before abrupt change: 1.71 m
• Mean thickness (70-90N) from ICESat in Spring 2007: 1.75 m (data from D. Yi and J. Zwally)
Arctic Sea Ice – Now and in the Future
Natural Variability Remains Important!NCAR CCSM3 Mean Ice
Thickness vs. Std. Dev. Ice Extent
• Natural variability increases with a thinning ice pack until the ice is gone
Arctic Sea Ice – Now and in the Future
Thus, Ice May Recover this Summer
• If we have a strong cyclonic pattern with attendant cold temperatures as in 1996, we may not set a new record in summer 2008.
September Ice Extent
0
2
4
6
8
10
12
1950 1970 1990 2010 2030 2050 2070 2090
Year
Ext
ent
(mill
ion
sq
-km
)
CCSM3 Run 6
Observations
Arctic Sea Ice – Now and in the Future
Does the Thin Ice Imply a Tipping Point?• If the simulated abrupt transitions are the manifestation of a “tipping
point”, then it is likely they would be preceded by a similar critical state
From Holland et al. in press
Solid line ice extent preceding the event, dashed line, extent after the event
Run 1: Year 2024 Run 2: Year 2025 Run 3: Year 2030
Run 4: Year 2027 Run 5: Year 2029
Arctic Sea Ice – Now and in the Future
However, Thin Ice Remains Important• Although there is not a “critical” ice thickness (or ice concentration) that
precedes rapid ice loss, it remains clear that an abrupt ice loss event is only possible if the ice has thinned adequately.
• Other GCMs also show thin ice is needed for large regions of the ice pack to melt completely out.
Annual Average Ice Thickness (m)
Sept
embe
r Ic
e E
xten
t (10
6 km
2 )
From Holland et al., in press
Arctic Sea Ice – Now and in the Future
Concluding Statements• Current models tend to underestimate the
observed rate of ice loss (Stroeve et al., 2007) and the large ice loss seen in 2007 typically doesn’t happen until mid-century.
• NCAR CCSM3 model simulations show 3 factors that contribute to abrupt transitions: Thinning sea ice Pulse-like increases in ocean heat transport to the
Arctic Positive surface albedo feedback.
• Ice loss in 2007 is similar in character to abrupt ice loss events simulated by CCSM3 later in this century.
Arctic Sea Ice – Now and in the Future
Concluding Statements (cont)
• Outstanding question remains whether the abrupt events occur due to a threshold or “tipping point”.
• Abrupt ice loss in NCAR CCSM3 seems to represent the interaction of large intrinsic Arctic variability with increasing forced change from rising GHGs.
• However, the result of an abruptly changing ice cover would be the same, with considerable impacts on the socio-economics, climate and biological systems in the Arctic.
• Summer 2008 is poised for yet another dramatic retreat of the sea ice cover.