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)

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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)

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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

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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).

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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

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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)

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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.