Yesterday, Dr. Meier commented on PIPS -VS- PIOMAS, here is Part 2
Here are some thoughts on three other sea ice issues addressed in recent posts: (1) concentration vs. extent, (2) the causes of the 2007 record minimum, and (3) whether it is possible for the Arctic to lose all its sea ice during summer. Again, I’m speaking only for myself and not as a representative of the National Snow and Ice Data Center or the University of Colorado at Boulder.
Concentration vs. Extent as a measure of the summer ice cover
Sea ice concentration fields are difficult to interpret during summer because of the significant melt that occurs. Areas of low concentration may include open water or ice with surface melt or some combination of both.
Atmospheric moisture, which is higher in the summer, can also affect the observed concentration (e.g., concentration values can change with passing storms). Extent is a more consistent and stable measure of the amount of surface covered by ice and is more legitimate in comparing the data from different years, which is why NSIDC uses extent. Because of the melt and atmospheric effects on concentration, it can be particularly misleading to Steve’s comparison of two single days of concentration data. If one wants to compare concentration, it is better to compare monthly averages, which smoothes out at least some of the ephemeral atmospheric and surface effects. Looking at anomalies for June from 1990 and 2010, there isn’t much difference in the middle of the Arctic (the 2010 anomaly is a bit lower) with lower anomalies in 2010 in coastal areas. Again though, in the central Arctic this may indicate more open water or simply more intensive surface melt. Comparisons with other years can be made at NSIDC’s Sea Ice Index.
Monthly concentration anomaly (in percent) for June 2010 (left) and June 1990 (right). Positive anomalies (higher than average concentration) are in red, negative anomalies (lower than average concentration) are in blue. Anomalies are relative to a 1979-2000 average.
Reasons behind the record low minimum 2007 ice extent
Ice motion has been discussed as a major reason for the record 2007 minimum. While ice motion was important, it was far from the only contributor. For example, Zhang et al. (2008) attribute ~30% of the ice volume loss to ice motion, with the remaining 70% due to pre-conditioning (i.e., thinner ice cover) and more solar heating. Kwok (2008) attributes 15% of the extent loss to motion of ice from the Pacific side across the pole toward the Atlantic. Ogi et al., (2008) calculated a 37% contribution of unusual winds (and resulting ice motion) to the September extent.
So, what else played a role? Kay et al. (2008) suggest that below normal cloud cover and enhanced solar energy played a role (though another study, Schweiger et al. [2008] suggest the role may have been limited). Steele et al. (2008) found anomously high sea surface temperatures during 2007, which enhanced melt. Lindsay et al. (2009) showed that by 2007, the ice cover had thinned enough to reach a threshold where a dramatic loss in extent was possible under conditions experienced during the summer of 2007. Furthermore, the thinner ice cover allows the ice cover to be blown by winds more easily (Haas et al., 2008) – i.e., the winds contributed to the low extent, but the thin ice enhanced the effect of the winds.
In other words, the 2007 minimum was not simply the result of unusual ice motion. It was the result of ice motion, enhanced melt, warmer ocean temperatures, and a long-term thinning trend seen in a variety of observations (Maslanik et al., 2007; Nghiem et al., 2007; Kwok and Rothrock, 2009). The same atmospheric conditions would not have led to such a low extent in earlier years when the ice pack was thicker. As Ogi et al. (2008) say (with clarifying comments by me italicized in brackets): “… the precipitous decline in September SIE [sea ice extent] in recent years is mainly due to the cumulative loss of multi-year ice: summertime SLP [sea level pressure] anomalies [which control the strength and direction of the wind anomalies] have played an important role in setting the timing of record lows, but the long term trend is mainly due to preconditioning [the thinning of the ice cover].”
Can the Arctic really become sea ice-free during summer?
It has been suggested that the Arctic really can’t lose all its sea ice during summer because there isn’t enough energy to melt all of the ice in the short summer. There are a couple of reasons why this thinking is faulty.
First, we know the Arctic can potentially lose all its sea ice during summer because it has done so in the past. Examination of several proxy records (e.g., sediment cores) of sea ice indicate ice-free or near ice-free summer conditions for at least some time during the period of 15,000 to 5,000 years ago (Polyak et al., 2010) when Arctic temperatures were not much warmer than today.
Second, the primary evidence provided for the implausibility of ice-free summers is the plot of daily temperature for regions poleward of 80 degrees N from the Danish Meteorological Institute. It shows that temperatures rise only a couple degrees above freezing for a period of about 75 days throughout the entire record since 1958. So there is no warming trend of the surface air temperatures in the high Arctic. So how could one possibly melt ice near the pole with summer temperatures at most a couple degrees above freezing with no increasing trend?
North of 80 degrees, the Arctic has been continuously covered by ice, even during summer, throughout the entire record (except for a small area briefly during summer 2007). As a result, any heat energy in the vicinity will be used to melt ice and will not raise temperatures. Only after the ice melts can the ocean absorb the energy allowing the ocean surface and the air above it to warm significantly. So the summer near-freezing temperatures don’t say anything much about the energy available to melt ice, only that ice is melting. (I’ll note that it is possible to have higher air temperatures locally, for example due to a weather system bringing in warm air from the south, but the average over the entire region will stay near freezing).
However, there are still only ~75 days of melt, which isn’t much time. But one needs to think about the overall process of what happens in the Arctic, not simply the direct solar energy. As temperatures increase, summer extent decreases, which allows more absorption of solar energy. This melts more ice, decreasing the extent and thinning the ice. Heat absorbed in the ocean away from the ice edge will warm the ocean waters, which will delay freeze-up in the fall. This leads to less ice growth further thinning of the ice. With warmer temperatures, melt will begin earlier in the spring and freeze-up will start later in the fall (as has been observed, e.g., Markus et al. [2009], Serreze et al. [2009], Stroeve et al. [2006]). This is a positive feedback (the sea ice-albedo feedback). Under this feedback, the ice will eventually become thin enough to melt completely most everywhere in the Arctic during a single summer.
There is little doubt in the sea ice community that during summer the Arctic can become ice-free and will become ice-free as temperatures continue to rise.
References
Haas , C., A. Pfaffling, S. Hendricks, L. Rabenstein, J.‐L. Etienne, and I. Rigor, 2008. Reduced ice thickness in Arctic Transpolar Drift favors rapid ice retreat, Geophys. Res. Lett., 35, L17501, doi:10.1029/2008GL034457.
Kay, J.E., T. L’Ecuyer, A. Gettelman, G. Stephens, and C. O’Dell, 2008. The contribution of cloud and radiation anomalies to the 2007 Arctic sea ice extent minimum, Geophys. Res. Lett., 35, L08503, doi:10.1029/2008GL033451.
Kwok, R., 2008. Summer sea ice motion from the 18 GHz channel of AMSR-E and the exchange of sea ice between the Pacific and Atlantic sectors. Geophys. Res. Lett., 35, L03504, doi:10.1029/2007GL032692.
Kwok , R. and D.A. Rothrock, 2009. Decline in Arctic sea ice thickness from submarine and ICESat records: 1958–2008, Geophys. Res. Lett., 36, L15501, doi:10.1029/2009GL039035.
Lindsay, R.W., J. Zhang, A. Schweiger, M. Steele, and H. Stern, 2009. Arctic sea ice retreat in 2007 follows thinning trend, J. Climate, 22, 165-176.
Markus , T., J. C. Stroeve, and J. Miller (2009), Recent changes in Arctic sea ice melt onset, freezeup, and melt season length, J. Geophys. Res., 114, C12024, doi:10.1029/2009JC005436.
Maslanik, J.A., C. Fowler, J. Stroeve, S. Drobot, J. Zwally, D. Yi, and W. Emery, 2007. A younger, thinner Arctic ice cover: Increased potential for extensive sea-ice loss, Geophys. Res. Lett., 34, L24501, doi:10.1029/2007GL032043.
Meier, W.N., 2005. Comparison of passive microwave ice concentration algorithm retrievals with AVHRR data in Arctic peripheral seas, IEEE Trans. Geosci. Remote Sens., 43(6), 1324-1337.
Nghiem, S.V., I.G. Rigor, D.K. Perovich, P. Clemente-Colon, J.W. Weatherly, and G. Neumann, 2007. Rapid reduction of Arctic perennial sea ice, Geophys. Res. Lett., 34, L19504, doi:10.1029/2007GL031138.
Ogi , M., I.G. Rigor, M.G. McPhee, and J.M. Wallace, 2008. Summer retreat of Arctic sea ice: Role of summer winds, Geophys. Res. Lett., 35, L24701, doi:10.1029/2008GL035672.
Polyak, L., and 17 others, 2010. History of sea ice in the Arctic, Quaternary Science Rev., 29, 1757-1778, doi:10.1016/j.quascirev.2010.02.010.
Schweiger , A.J., J. Zhang, R.W. Lindsay, and M. Steele, 2008. Did unusually sunny skies help drive the record sea ice minimum of 2007?, Geophys. Res. Lett., 35, L10503, doi:10.1029/2008GL033463.
Serreze, M.C., A.P. Barrett, J.C. Stroeve, D.N. Kindig, and M.M. Holland. 2009. The emergence of surface-based Arctic amplification, The Cryosphere, 3, 11–19.
Steele, M., W. Ermold, and J. Zhang, 2008. Arctic Ocean surface warming trends over the past 100 years, Geophys. Res. Lett., 35, L02614, doi:10.1029/2007GL031651.
Stroeve, J., T. Markus, W.N. Meier, and J. Miller, 2006. Recent changes in the Arctic melt season, Ann. Glaciol., 44, 367-374.
Zhang, J., R. Lindsay, M. Steele, A. Schweiger, 2008. What drove the dramatic retreat of arctic sea ice during summer 2007?, Geophys. Res. Lett., 35, L11505, doi:10.1029/2008GL034005.
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From a carefull look at the graphic:
“The urgent need to act can’t be overstated” (climateprogress)
I am concerned, very concerned about my grand children.
[snip – ad hom, insulting, and juvenile – you’ve been warned – permanent troll bin for you now Luis]
Thank you for this. The science of Arctic ice is fascinating.
>> Henry chance says:
July 14, 2010 at 11:18 am
From carefull look at the graphic:
“The urgent need to act can’t be overstated” (climateprogress)
I am concerned, very concerned about my grand children. <<
I'm leaving a message for my grandchildren to stay off the Arctic ice.
I don’t know. I quit reading after “proxy”. That’s even worse than a Godwin.
How come the German overflight seems to be ignored by everyone?
Still no evidence it is anything to do with CO2.
Still no evidence that it is anything to do with Anthropogenic CO2
Still no evidence that no arctic ice would be a bad thing.
Still no evidence that building tens of thousands of wind turbines will do diddly squat about melting ice, global “average temperatures” or anything else except transferring huge amounts of loot from the average little man to the politicians, city slickers and “climate scientists” and denying the third world poor any prospect of hope or progress.
The final paragraph: “There is little doubt in the sea ice community that during summer the Arctic can become ice-free and will become ice-free as temperatures continue to rise.”
In my opinion, if Dr Meier had been smart he would have stated “ice-free IF temperatures continue to rise”. He clearly seems to believe in AGW and the fact that summer Arctic sea ice has increased since 2007 and atmospheric temperatures have remained more or less constant since 1998 does not affect his judgement. He is probably right in what he is writing except his emphasis on the unquestionable forecast (I would say belief) that global temperatures will continue to rise cause by AGW. On the other hand he may not secretly include himself in the “sea ice community” or they are all (in that community) desperate to appear “on message” with Obama and company. If he said otherwise he might be out of a job. Dangerous times for those in official jobs who would like to express their own thoughts.
“There is little doubt in the sea ice community that during summer the Arctic can become ice-free and will become ice-free
asif temperaturescontinue toresume a rise.”There you go Walt, fixed.
Instead of an overall area extent, why not report it by sectors of, say, 45 degree wedges radiating from the geographic north pole? That might iron out some of the variability due to wind effects?
“Still no evidence it is anything to do with CO2.”
I think this can’t be emphasized enough….
nc says:
July 14, 2010 at 11:44 am
How come the German overflight seems to be ignored by everyone?
Link, please?
Walt
A couple tangentially related questions:
There appear to be mechanisms that help to balance Global Sea Ice such that when when one pole is above average;
http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/seaice.anomaly.antarctic.png
the other pole is often below average;
http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/seaice.anomaly.arctic.png
and Global Sea Ice remains reasonably stable:
http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/global.daily.ice.area.withtrend.jpg
Here is a good overlay showing the relationship between Arctic and Antarctic Sea Ice Area:
http://www.robertb.darkhorizons.org/seaice.anomaly.Ant_arctic.jpg
Why are there no Global Sea Ice Extent charts on the NSIDC website?
On the right side of this page;
http://nsidc.org/data/seaice_index/
in the drop down, it would seem a logical to add Global. Can this be done? Is there a reason why NSIDC does not offer this information?
Also, we’ve already tread over this ground, but NSIDC’s choice to exclude data after 2000 from their standard deviation calculations makes the “normal” range misleadingly narrow, such that both the Arctic;
http://nsidc.org/data/seaice_index/images/daily_images/N_stddev_timeseries.png
and Antarctic;
http://nsidc.org/data/seaice_index/images/daily_images/S_stddev_timeseries.png
are currently outside this range. Why does NSIDC exclude data after 2000 from their calculation? Can the data through 2008 be added to help dispel the perception that NSIDC excludes this data in order to make the current Arctic Sea Ice Extent look misleadingly anomalous?
An excellent paper. Hpwever, I have one major quibble. Walt writes “There is little doubt in the sea ice community that during summer the Arctic can become ice-free and will become ice-free AS temperatures continue to rise.” (My capitals)
This implies that global temperatures are going to go on rising. I think it is much more scientific to replace “as” with “if”. i.e. ” will become ice-free IF temperatures continue to rise”
But then comes the important question. How long might it be before we see an ice free summer in the Arctic?
I agree with Martin Brumby.
I would condense his statements to: ‘So what?’ Unlike the alarmist crowd, we all know that the climate always changes, and that the planet has been naturally warming since the LIA.
The alarmist conjecture claims that the warming is caused by human activity. But the hypothesis that the observed temperature changes are a consequence of natural variability has never been falsified.
All this arm-waving over what is a natural, regional event happens because out of all the climate scares pronounced by co-opted scientists, the only one that hasn’t been completely debunked is the Arctic ice trend.
But unless the Antarctic begins to trend the same way, then what is occurring in the Arctic must be seen as regional climate variability. The burden of showing that CO2 is the cause is entirely on the alarmist scientists. So far, they have shown us models, opinions, assumptions, conjectures, and everything else — except for empirical, testable evidence.
John Peter says:
July 14, 2010 at 11:57 am
…they are all (in that community) desperate to appear “on message” with Obama and company. If he said otherwise he might be out of a job. Dangerous times for those in official jobs who would like to express their own thoughts.
Silly. Whenever I see comments like this, my first thought is “gee, then how did they all survive Bush/Cheney for 8 years, as they expressed the same, and at that time very unpopular in the Executive Branch, scientific opinions?”
Maybe, just maybe, it really is the prevailing view…
Smokey,
So just what is this “natural variability”? Just how does it work? By what means is it doing this? What mechanism is in play? How do we scientifically explore this “natural variability”? Or is it, as Dr. Spencer says, just what happens, and there is no reason or possibility of explaining it?
A precondition that contributed to the 2007 melt was further wind-driven loss of thick ice in 2006. Meier should be a bit more upfront about that point.
so the arctic has had ice free summers in the recent past, and may see them again if it keeps warming.
meanwhile, it’s snowing in july in canada-
http://www.theweathernetwork.com/news/storm_watch_stories3&stormfile=jaspersnow_13_07_2010?ref=ccbox_weather_bottom_title
Jakers,
As Walt pointed out in his paper, there is pretty strong evidence that the arctic may have indeed been ice-free during some times in the period of 15,000 to 5000 years ago. He also says at that time it was NOT MUCH WARMER THAN NOW (which means it WAS INDEED warmer than now.
Since there was no man-made CO2 15,000 to 5000 years ago, this ice-free condition in the Arctic only be attributed to… wait for it… NATURAL VARIABILITY.
The term “natural variability” is not mystical in any way, shape or form. Climate CHANGES. It always HAS changed, and it always WILL change, and this will happen regardless of what human beings do. We MAY have some influence on the direction and/or magnitude of climate change, but that has yet to be conclusively proven. So far all climate change from 1850-present is well within the previous range of documented climate changes. For example, Walt does acknowledge that it was indeed warmer (albeit not much warmer) at least at some period or periods of time from 15,000 to 5000 years ago compared to now.
So, by the same token, antarctic ice is increasing because of the continued warming?
“Again, I’m speaking only for myself and not as a representative of the National Snow and Ice Data Center or the University of Colorado at Boulder.”
Hopefully the two “versions” would be identical, as we are paying for the official one. The good Doctor’s presentation is much appreciated both for its tone as well as its content. His “AGW” tendency is understandable but needs factual verification if it is to be chosen over the influence of natural variation.
jakers ,
there’s a paper out (Chylek et al. 2010) which seems to consider the mechanism which explains arctic versus antarctic trends to be associated with the AMO. The paper does indicate though that the positive phase of the AMO will soon come to an end.
OK, so it’s “natural variation” then. Well, if you can’t identify the mechanism, the ‘how’ of its workings, then how is it not mystical?
This blog is blessed by Dr. Meiers obvious love of teaching.
So if something other than AGW caused an ice free arctic summer a few thousand years ago, could Walt Meier explain why he is convinced it is AGW this time and not the same mechanism as the last time?
Also, as it appears that Antarctic ice is rising above average about the same amount as the Arctic is below average, the net anomaly for humanity to worry about is……zero?