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Kevin O'Neill

Recovery mechanisms of Arctic summer sea ice S. Tietsche, D. Notz, J. H. Jungclaus, and J. Marotzke.

IPCC climate models do not capture Arctic sea ice drift acceleration: Consequences in terms of projected sea ice thinning and decline P. Rampal, J. Weiss, C. Dubois, J.-M. Campin

Daniel Bailey

The Arctic’s rapidly shrinking sea ice cover: a research synthesis J. Stroeve, M. Serreze, M. Holland, J. Kay, J. Malanik, A. Barrett
Climatic Change (2012) 110:1005–1027
DOI 10.1007/s10584-011-0101-1

Abstract

The sequence of extreme September sea ice extent minima over the past decade suggests acceleration in the response of the Arctic sea ice cover to external forcing, hastening the ongoing transition towards a seasonally open Arctic Ocean. This reflects several mutually supporting processes.

Because of the extensive open water in recent Septembers, ice cover in the following spring is increasingly dominated by thin, first-year ice (ice formed during the previous autumn and winter) that is vulnerable to melting out in summer. Thinner ice in spring in turn fosters a stronger summer ice-albedo feedback through earlier formation of open water areas. A thin ice cover is also more vulnerable to strong summer retreat under anomalous atmospheric forcing.

Finally, general warming of the Arctic has reduced the likelihood of cold years that could bring about temporary recovery of the ice cover. Events leading to the September ice extent minima of recent years exemplify these processes.

Money Quotes:

"Schefer et al. (2009) argue that before a system is close to a critical threshold, there is a ‘critical slowing down’, i.e., the system becomes increasingly slow in recovering from perturbations which leads to an increase in the ‘memory’ of the system."
And
"With these processes described above working together to support further ice loss, combined with the greater ease at which anomalous atmospheric forcing can cause dramatic summer ice loss, the system may be poised to undergo rapid change."

Neven

Thanks, Kevin and Daniel! Those are excellent papers, just the things needed here. I will put them on the list, but it could take a while for me to digest them.

Daniel Bailey

This one will cause the denialists to Cry Havoc! And let slip the dogs of war!

Observations reveal external driver for Arctic sea-ice retreat
Dirk Notz, Jochem Marotzke
Geophysical Research Letters, 2012; 39 (8)
DOI: 10.1029/2012GL051094

Open-copy available here:
http://www.mpimet.mpg.de/fileadmin/staff/notzdirk/2012GL051094.pdf

Abstract
The very low summer extent of Arctic sea ice that has been observed in recent years is often casually interpreted as an early-warning sign of anthropogenic global warming. For examining the validity of this claim, previously IPCC model simulations have been used. Here, we focus on the available observational record to examine if this record allows us to identify either internal variability, self-acceleration, or a specific external forcing as the main driver for the observed sea-ice retreat.

We find that the available observations are sufficient to virtually exclude internal variability and selfacceleration as an explanation for the observed long-term trend, clustering, and magnitude of recent sea-ice minima. Instead, the recent retreat is well described by the superposition of an externally forced linear trend and internal variability. For the externally forced trend, we find a physically plausible strong correlation only with increasing atmospheric CO2 concentration.

Our results hence show that the observed evolution of Arctic sea-ice extent is consistent with the claim that virtually certainly the impact of an anthropogenic climate change is observable in Arctic sea ice already today.

Conclusions
In this contribution, we have shown that the following conclusions can be drawn from an analysis of the available observational record:

1. Internal variability as estimated from pre-satellite observations cannot explain the recent retreat of Arctic sea ice.

2. The observational record shows no signs of selfacceleration and hence no signs of a possible ‘tipping’.

3. The satellite record is well described by a linear trend onto which internal variability is superimposed. The magnitude of this superimposed internal variability is very similar to that of the pre-satellite record.

4. The most likely explanation for the linear trend during the satellite era from 1979 onwards is the almost linear increase in CO2 concentration during that period.

Science News Daily Article here:
http://www.sciencedaily.com/releases/2012/05/120502091932.htm

Daniel Bailey

Check out Fig 4 for some eye-candy...
http://www.skepticalscience.com/pics/Notz2012.jpg

Neven

This one will cause the denialists to Cry Havoc! And let slip the dogs of war!

Well, if it's that bad, I guess it merits a blog post of its own. ;-)

Thanks, Daniel.

Artful Dodger

Hi folks,

Long-time readers will recall the international scientific voyage lead by Dr. David Barber on the Canadian Icebreaker Amundsen during the ASI blog's first Summer. That mission brought together a multidisciplinary team, and took them through the heart of the pack ice in the Beaufort Sea and the Central Arctic Basin, North of the CAA.

Well folks, the results are in!

Barber et.al (2012) Change and variability in sea ice during the 2007-2008 Canadian International Polar Year program
Published online: 03 May 2012

Here are the studies 5 major conclusions about Arctic Sea Ice:

  1. In the Amundsen Gulf, at the western end of the Northwest Passage, open water persists longer than normal and winter sea ice is thinner and more mobile.
  2. Large areas of summer sea ice are becoming heavily decayed during summer and can be broken up by longperiod waves being generated in the now extensive open water areas of the Chukchi Sea.
  3. Cyclones play an important role in flaw leads-regions of open water between pack ice and land-fast ice. They delay the formation of new ice and the growth of multi-year ice.
  4. Feedbacks involving the increased period of open water, long-period wave generation, increased open ocean roughness, and the precipitation of autumn snow are all partially responsible for the observed reduction in multiyear sea ice.
  5. The atmosphere is observed as remaining generally stable throughout the winter, preventing vertical entrainment of moisture above the surface.

    The full text of the paper is available as a PDF at the link above. Enjoy!

Artful Dodger

New paper published in Geophysical Research Letters on Aug 25 - Stroeve et. al (2012) "Trends in Arctic sea ice extent from CMIP5, CMIP3 and observations"

Key Points:

  • CMIP5 models continue to underestimate rate of sea ice loss
  • CMIP5 models are more consistent with observations than CMIP3
  • CMIP5 suggests 60% of 1979-2011 rate of decline is externally forced

Abstract:

The rapid retreat and thinning of the Arctic sea ice cover over the past several decades is one of the most striking manifestations of global climate change. Previous research revealed that the observed downward trend in September ice extent exceeded simulated trends from most models participating in the World Climate Research Programme Coupled Model Intercomparison Project Phase 3 (CMIP3). We show here that as a group, simulated trends from the models contributing to CMIP5 are more consistent with observations over the satellite era (1979–2011). Trends from most ensemble members and models nevertheless remain smaller than the observed value. Pointing to strong impacts of internal climate variability, 16% of the ensemble member trends over the satellite era are statistically indistinguishable from zero. Results from the CMIP5 models do not appear to have appreciably reduced uncertainty as to when a seasonally ice-free Arctic Ocean will be realized.

Citation:

Stroeve, J. C., V. Kattsov, A. Barrett, M. Serreze, T. Pavlova, M. Holland, and W. N. Meier (2012), Trends in Arctic sea ice extent from CMIP5, CMIP3 and observations, Geophys. Res. Lett., 39, L16502, doi:10.1029/2012GL052676.

Hans Kiesewetter

CMIP5 suggests 60% of 1979-2011 rate of decline is externally forced. What does this mean? What is the other 40%?
I tried to download the article but: paywall! Google found an other interesting document from Stroeve: www.cesm.ucar.edu/working_groups/Polar/presentations/2012/stroeve.pdf.

Seke Rob

That means those going right up on 2 hindlegs also known as Homo Sapiens Sapiens: http://en.wikipedia.org/wiki/Global_warming

We've seen so many variations on this theme. CO2 is 5%, but the feedback, such as more water vapor is 95%. In the total state of present, this one though wishes to attribute 60% to us is my understanding.

Artful Dodger

Hi Hans,

Notz and Marotzke (2012) suggest the external forcing is the steadily increasing amounts of atmospheric CO2. Below is Fig. 4 from their paper.

Notz, D. and J. Marotzke (2012), Observations reveal external driver for Arctic sea-ice retreat, Geophys. Res. Lett., 39, L08502, doi:10.1029/2012GL051094.

Notice the strong correlation between decrease in SIE and CO2 concentration over time. Also note the lack of correlation between SIE decrease and these 3 variables:

  • It's the Sun,
  • It's the Pacific Decadal Oscillation,
  • It's the Arctic Oscillation

Cheers,
Lodger

Timothy Chase

Seke Rob wrote:

We've seen so many variations on this theme. CO2 is 5%, but the feedback, such as more water vapor is 95%. In the total state of present, this one though wishes to attribute 60% to us is my understanding.
More like 19% for CO2 and 50% for water vapor, where the residence time for water vapor is on the order of 10 days and rapidly adjusts to temperature and thus other forcings.

Please see:

As can be seen in Table 2, the most important overlaps are between water vapour and clouds, followed by water vapour and CO2. Once they are attributed, the total net effects for water vapour, clouds, CO2 and the other forcings are 50%, 25%, 19% and 7%, respectively. For the clear sky calculation, we can remove the clouds and examine the allocation of the remaining LW absorption to get 67%, 24% and 9% for water vapour, CO2 and the other forcings respectively.

Schmidt, G.A., R. Ruedy, R.L. Miller, and A.A. Lacis, 2010: The attribution of the present-day total greenhouse effect. J. Geophys. Res., 115, D20106, doi:10.1029/2010JD014287.

Timothy Chase

Correction: I had written above:

...thus other forcings.
However, technically, given its versy short residence time, water vapor is a feedback, not a forcing.

Seke Rob

Timothy, I would have done better to qualify that as and example of variations going around in cause and effect [feedback]. The residence time *was* 10 days for water vapor. I've seen here blog entries of authoritative toned 11 days, but other sources speak of acceleration... 9 days. I'm leaning towards the shorter lifetime of a water mol in the atmosphere... sooner rain out (of course not washing out CO2 as some happy campers readily will postulate in the FS camp).

Seke Rob

P.S. Thanks for the paper link. I've seen your numbers too. WV is beyond a shadow of a doubt [on my part] a feedback... a resultant of everything else going around and coming in. Take CO2 out and temps drop about 33-35C... numbers on that too vary, but ice-ball earth would return real quick, a Holocene optimal axis alignment for maximum NH continental insolation or not.

Timothy Chase

Seke Rob wrote:

I've seen your numbers too. WV is beyond a shadow of a doubt [on my part] a feedback... a resultant of everything else going around and coming in.

Regardless a figure of 5% for carbon dioxide and 95% for water vapor is incorrect. Depending upon how you calculatee it, carbon dioxide is responsible for 14-25% and water vapor 39-62%.

Please see:

As expected, the joint effects of removing water vapour and CO2 or water vapour and clouds is greater than the sum of effects of removing each component individually. In line with previous results, we nd that water vapour accounts for 39% if removed, and 62% of the net LW absorption if acting alone, similarly, clouds account for 15 and 36% and CO2, 14 and 25%.

Schmidt, G.A., R. Ruedy, R.L. Miller, and A.A. Lacis, 2010: The attribution of the present-day total greenhouse effect. J. Geophys. Res., 115, D20106, doi:10.1029/2010JD014287.

Seke Rob wrote:

I've seen here blog entries of authoritative toned 11 days, but other sources speak of acceleration... 9 days. I'm leaning towards the shorter lifetime of a water mol in the atmosphere... sooner rain out (of course not washing out CO2 as some happy campers readily will postulate in the FS camp).
I said "... on the order of..." but in either case the residence time of water vapor actually increases with time.

Please see:

There are a number of ways of measuring the strength of the atmospheric circulation, but by this particular measure, the circulation must weaken as the climate warms. We can, alternatively, speak of the mean residence time of water vapor in the troposphere as increasing with increasing temperature (Roads et al., 1998; Bosilovich et al., 2005).

Held I M and Soden B J 2006 Robust responses of the hydrological cycle to global warming J. Clim. 19 5686–99

I believe this is in part due to Arctic amplification reducing the temperature gradient between the Arctic and lower latitudes and thus reducing the strength of the jet stream, which also leads to an increase in the amplitude of Rossby waves as well as increased blocking events, both of which result in increased extreme weather.

Please see:

Francis, J. A. and S. J. Vavrus, 2012: Evidence Linking Arctic Amplification to Extreme Weather in Mid-Latitudes, Geophys. Res. Lett., Vol. 39, L06801, doi:10.1029/2012GL051000

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