Guest post by Dr. Walt Meier, National Snow and Ice Data Center
Winds, Temperatures, and Arctic Sea Ice Extent
As the summer sea ice melt season gets into high gear, I thought I’d do a post on sea ice processes and other tidbits about sea ice that may be useful as people watch the seasonal sea ice extent decline. My thanks to Anthony for the opportunity to share this information.
Often, much of the focus in the news is on the effect of warming air temperatures on observed decline in Arctic sea ice extent, such as in the The Economist article. Others have suggested, such as in last Saturday’s post, that winds are the key to understanding the extent decline. These are not competing viewpoints, but reflect complementary contributions to changes in sea ice extent. For a full description of how sea ice changes – day-by-day, month-by-month, and over the years and decades – both wind and air temperatures (along with other factors, e.g., the oceans) need to be considered.
Winds and daily variations in extent
Winds primarily affect sea ice extent by pushing ice around, either spreading the ice out over larger area (increasing extent) or compressing it into a smaller area (decreasing extent). Often, day-to-day changes in sea ice extent are primarily due to changes in winds and not freezing or melting. The winds can also open areas of water within the ice-pack, called leads, if they push floes of ice apart. Thus, even during winter, there are open water areas or areas of thin ice (as leads begin to re-freeze) throughout the ice-pack. It is this feature that has allowed submarines to surface at the North Pole since the 1950s, even though the overall sea ice thickness was much greater in the 1950s compared to today. (In other words, surfacing subs at the North Pole are not an indicator of Arctic sea ice conditions.)
Winds and interannual changes in extent
Winds are variable, blowing at different directions and speeds. Thus over time, the effect of the winds settles into an average pattern and their net effect on extent is smaller relative to temperatures. However, average wind patterns can themselves vary over longer periods of time due to large-scale climate oscillations, most notably for the Arctic Oscillation (AO). During the late 1980s and early 1990s, the AO was often in a positive mode that favors the motion of older, thicker sea ice out of the Arctic. The remaining younger, thinner ice cover was more easily melted completely in the subsequent summers. This contributed to some of the summer extent decline during that period, as was noted in papers by Rigor and Wallace (2004) and Rigor et al. (2002). However, in recent years, this relationship appears to have broken down. After very strongly negative AO winters in 2009-2010 and 2010-2011, the summer sea ice again reached low levels (Stroeve et al., 2011).
Winds and summer extent
Even over a season, variation in the winds can play an important role. They were a key factor in the record low extent of 2007, as noted for example by Ogi and Wallace (2012) and Zhang et al. (2008) , who found that ~30% of the record low extent could be attributed to unusual ice motion (driven by the winds). According to Ogi et al. (2010), 50% of the year-to-year variation in extent can be explained by the variation in winds. Ogi and Wallace (2012) noted that if the wind patterns were similar to 2007, the minimum extent during 2010 and 2011 would have likely been as low as or lower than 2007.
Effects of winds and temperature on long-term changes in sea ice
Winds can also influence the long-term trend in extent. Ogi et al. (2010) estimated that up to 33% of the trend for 1979-2009 could be explained by winds. One mechanism for this long-term influence is via long-term changes in the winds, which have been noted by Ogi et al. (2010) and Smedsrud et al. (2009). Another effect on extent due to winds is in how effective winds are pushing the ice around. Spreen et al. (2011) noted that while some increase in wind speed is observed (in agreement with the Ogi and Smedsrud papers), the speed of the ice increased much more. In other words, the winds are becoming more effective at pushing the ice around.
The motion of sea ice is affected not only by winds (and other smaller factors), but also by the ice itself. Thinner ice is more easily pushed around by the winds than thicker ice (Haas et al., 2008). And the sea ice cover has been getting substantially thinner through the loss of older, thicker ice (e.g., Maslanik et al., 2011; Kwok and Rothrock, 2009). Zhang et al. (2008) found that thinner ice cover was a crucial factor in the 2007 ice loss and if the ice pack were thicker, a record low would not have occurred under the same winds. As mentioned above, some of this loss can be ascribed to the positive AO of a couple decades ago. However, since then the AO has been in a mostly neutral or negative mode and yet older ice has continued to be lost. For those interested, a nice animation of changes in ice age can be seen at the NOAA Climate Watch website.
Thus, the long-term thinning trend is primarily a reflection of additional energy from globally warming temperatures. Thick ice still moves out of the Arctic (or melts within the Arctic), but the additional energy in the Arctic prevents the replenishment of thicker ice at the same pace. The system is out of equilibrium and older, thicker ice continues to decline (though with some year-to-year variability). The additional energy is not always indicated by warmer local air temperatures though, especially in ice-covered areas. The Danish Meteorological Institute (DMI) air temperature estimates for north of 80° N, shows summer temperatures just above freezing during summer and there is little or no trend. This is because the additional energy is used to melt the surface of the ice and not warm the atmosphere, which stays near the melting point through the summer.
Conclusion
So, overall, the long-term decline in sea ice is mostly due to increasing temperatures leading to thinner ice cover that is more easily melted completely during summer. Winds accelerate or slow the long-term decline through the motion of thick ice out of the Arctic for period of up to a few years. The effects of winds may have longer-term consequences because their effect on ice motion increases as ice thins. The interplay between the two factors – wind and temperature – is perhaps best exemplified by the estimates for September sea ice extent in the recently released Sea Ice Outlook. There is a wide spread between different outlooks – about 500,000 square kilometers; even the uncertainties of a single method are on the same order of magnitude. That 500,000 square kilometer uncertainty reflects uncertainty in how the winds will vary this summer. However, all of the outlook contributions are more than 1.5 million square kilometers below normal, which demonstrates the effect of the long-term warming trend.
References
Haas, C., A. Pfaffling, S. Hendriks, 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.
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.
Maslanik, J., J. Stroeve, C. Fowler, and W. Emery (2011), Distribution and trends in Arctic sea ice age through spring 2011, Geophys. Res. Lett., 38, L13502, doi:10.1029/2011GL047735.
Ogi, M., K. Yamazaki, and J. M. Wallace (2010), Influence of winter and summer surface wind anomalies on summer Arctic sea ice extent, Geophys. Res. Lett., 37, L07701, doi:10.1029/2009GL042356.
Ogi, M. and J. M. Wallace (2012), The role of summer surface wind anomalies in the summer Arctic sea ice extent in 2010 and 2011, Geophys. Res. Lett., 39, L09704, doi:10.1029/2012GL051330.
Rigor, I.G. and J.M. Wallace (2004), Variations in the Age of Sea Ice and Summer Sea Ice Extent, Geophys. Res. Lett., v. 31, doi:10.1029/2004GL019492.
Rigor, I.G., J.M. Wallace, and R.L. Colony (2002), Response of Sea Ice to the Arctic Oscillation, J. Climate, v. 15, no. 18, pp. 2648 – 2668.
Smedsrud, L. H., Sirevaag, A., Kloster, K., Sorteberg, A., and Sandven, S. (2011), Recent wind driven high sea ice area export in the Fram Strait contributes to Arctic sea ice decline, The Cryosphere, 5, 821-829, doi:10.5194/tc-5-821-2011.
Spreen, G., R. Kwok, and D. Menemenlis (2011), Trends in Arctic sea ice drift and role of wind forcing: 1992–2009, Geophys. Res. Lett., 38, L19501, doi:10.1029/2011GL048970.
Stroeve, J. C., J. Maslanik, M. C. Serreze, I. Rigor, W. Meier, and C. Fowler (2011), Sea ice response to an extreme negative phase of the Arctic Oscillation during winter 2009/2010, Geophys. Res. Lett., 38, L02502, doi:10.1029/2010GL045662.
Zhang, J., R. Lindsay, M. Steele, and 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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Latest graphs are on the WUWT Arctic Sea Ice page
Related articles
- The Economist Provides Readers With Erroneous Information About Arctic Sea Ice (wattsupwiththat.com)
- Global warming: Arctic sea ice extent dips toward new lows (summitcountyvoice.com)
- Will Arctic Sea Ice Reach Record Low This Year? (news.discovery.com)
@David Falkner
“Second, I want to present my major issue here. Your conclusion is that increasing Arctic temperatures are the main driver of ice decrease, yet the major swings in Arctic temperature are during the colder months according to the Denmark Institute temperatures. It is readily apparent to anyone with an understanding of the mechanics of statistics that the temperatures are wildly variable in the other seasons, but in melt season they are remarkably consistent. This can be seen by comparing the DMI actuals (red line) to the DMI averages (green line) in the WUWT Sea Ice tab (click your way through the years, readers). I wondered if you, or anyone else could quantify the effect of CO2 on this temperature variability? ”
Dr Meier addressed this issue:
“The additional energy is not always indicated by warmer local air temperatures though, especially in ice-covered areas. The Danish Meteorological Institute (DMI) air temperature estimates for north of 80° N, shows summer temperatures just above freezing during summer and there is little or no trend. This is because the additional energy is used to melt the surface of the ice and not warm the atmosphere, which stays near the melting point through the summer.”
First of all thanks to Dr Meier for his article – I learnt from it. I hope he manages to filter out valid questions from the comments of those who would never ever believe him.
It seems to me that the central problem of attribution is that we only have accurate data from 1979 to the present when the trend was mainly in one direction. It would help to resolve the issue if we had a consistent data set going back over 100 years or more. (Manfred made a similar point.) This of course would mean sitting down with dusty archive records in Russian, Icelandic, Finnish etc and trying to make consistent sense out of them. Not half as much fun as jetting off to Rio with people who share your eschatological view of humanity’s future.
Note also that the current temp is slap bang on the 40 year average, so how can only really say increased temperature is the cause.
While I’m far from convinced that the position Dr Meier sets forth is entirely correct, at least it is clearly and intelligently set forth — which is a refreshing change from the usual climate-crap, dubious math, worse logic, cherry-picking, blatant manipulation of appallingly bad data, ad hominem attacks on dissent, etc that afflicts so many climate discussions. And he does address issues like the lack of dramatic atmospheric warming in the high Arctic. I would like to see a bit more about assertion that energy is going into ice melt rather than warming. It’s plausible. And I haven’t encountered it before. But some evidence would be nice. (Where is the energy coming from? The sun hasn’t brightened? The mid latitudes haven’t warmed much? Has cloud cover changed?) Anyway, something is clearly going on in the Arctic and has been for a decade. This is the best discussion I’ve seen of the situation.
Thanks to you and Dr Meier for presenting it.
I will remind all readers, and the good Dr Meier himself – that it was this WUWT group that first plotted all of the historic DMI daily temperatures at 80 north latitude since 1958.
And, the results of that plot of daily temperatures during the melting season?
Since 1958, summer temperatures in the actual Arctic Ocean where all of the sea ice actually is have declined since 1958, and the recent rate of decline is increasing!
Since summer temperatures immediately above the ice match the only time of year when solar radiation can actually reach the ice surface, the greenhouse gas feedback/effect of CO2 on re-radiated radiation from the ice cannot be true: At 4.5 million km^2, the Arctic ice extents reflect a “cap” that can be approximated as that region between latitude 79.5 and the pole. Or, in round numbers, 80 north to the pole.
So his excuse that some kind of “summer heat increase” is melting ice rather than increasing the temperature of the air is incorrect. There is NO summer heat increase that is actually measured at the place where the ice is!
I was wondering what effect the regional changes in salinity were having on the Arctic sea ice.
Ref, January 04, 2012: http://www.jpl.nasa.gov/news/news.cfm?release=2012-002
NASA Finds Russian Runoff Freshening Canadian Arctic
A strengthening of the west-east Arctic Oscillation has made an ocean circulation pattern go the other way. Historically the Russian river runoff flowed westward, ending up in the Eurasian basin between Russia and Greenland. Now it goes eastward to the Beaufort Sea (near western Canada and Alaska).
(Arctic reference map showing the assorted seas for the other people who wonder where the hell they all are.)
The Canada Basin (see large version of salinity change map from NASA article) has freshened considerably.
As the freezing point of water drops as salinity increases, I commonly find -2°C cited for “average” seawater, this should lead to greater extent in the Beaufort Sea and Canada Basin regions as ice would be formed when the water is warmer than would have historically supported ice growth. Offhand I guess the main difference would be additional thin ice at the end of the freeze-up season, prone to breakup by winds.
The reverse should also hold true. As noted on the large salinity change map, the area around the Laptev Sea has seen significant increases in salinity.
As mentioned in the Alfred Wegener Institute press release in a recent WUWT post, SMOS Satellite imagery suggests NE passage to open soon – ‘primarily attributable to the wind’, about the Laptev Sea:
The increase in salinity would lead to a decrease in ice production, as has been noted.
The strengthening of the Arctic Oscillation appears to be primarily influencing the decreases in extent and multi-year ice, with more breakup from stronger winds and changes in ocean circulation. As Julienne Stroeve noted in March:
With the winds of the predominantly-positive AO having grown strong enough to reverse a longstanding ocean current, I would expect this has lead to stronger west-to-east ocean currents around Greenland, where the multi-year sea ice likes to hang out, thus leading to increased amounts of multi-year ice being flushed out of the Fram Strait to the east of Greenland, and the decline of the Arctic sea ice.
So one question would be, since the energy for winds normally comes from temperature differences and ice is a source of coldness, will the sea ice decline lead to the AO weakening, to where either an equilibrium or a reversal of the decline occurs?
One other question would be, as I wondered at the beginning of this thought train, how much has the changes in salinity affected the sea ice? And if it is significant, if the AO weakens, the Arctic Ocean currents weaken and that freshwater starts flowing back to the Eurasian Basin and the salinity reasserts the historical distributions, won’t that yield a quick whipsawing back to increasing ice?
“I would like to see a bit more about assertion that energy is going into ice melt rather than warming. It’s plausible. And I haven’t encountered it before. But some evidence would be nice. ”
It is widely reported in the litterature. See for instance:
Variations in Surface Air Temperature Observations in the Arctic, 1979–97
http://ruby.fgcu.edu/courses/twimberley/EnviroPhilo/Rigor.pdf
The authors state (p 907)
“The ice and snow masses in the polar regions interact
with the global climate system in a myriad of complex
ways. During most seasons, SAT [Surface Air Temperature] trends can be studied
by simple statistical methods, but during summer, because
these masses hold the SAT to the melting point
of sea ice, detection of changes in SAT must rely on
other, less direct indicators such as the length of the
melt season.”
other source:
Vertical structure of recent Arctic warming
http://ic.ucsc.edu/~acr/BeringResources/Articles%20of%20interest/Central%20Artic/Graversen%20et%20al%202008.pdf
The authors state (p 54)
“We note that the lack of amplification near the surface in summer is
consistent with expectations because surface air temperatures over
the Arctic Ocean are constrained to be close to the freezing point
owing to the melting of sea ice”
Dr. Meier,
You wrote: “Thus, the long-term thinning trend is primarily a reflection of additional energy from globally warming temperatures.”
I draw your attention to the “models versus observations 1958 – 2011” graph, posted at WUWT on June 15th and ask to know the authority by which you assert your statement?
http://wattsupwiththat.com/2012/06/15/james-hansens-climate-forecast-of-1988-a-whopping-150-wrong/
Steve Goddard has also commented on the meaning of Hansen’s 1988 scenarios.
http://stevengoddard.wordpress.com/2012/06/15/clarifying-hansens-scenarios-worse-than-it-seems/
So compered with the warmingperiod leading to the MWP…whats the difference?
Given that the summer temperatures in the Arctic have not risen it should be clear that little heat is transferred from the air to the ice. The ocean must supply the heat and changes in the ocean current flow must be responsible. What are the present and past flow rates in and out of the arctic ocean. Comparing the specific heat of ice, water and air it should be clear that ice would have a large moderating influence on temperature excursions during the summer and open water during the winter.
Ron Manley said;
“It seems to me that the central problem of attribution is that we only have accurate data from 1979 to the present when the trend was mainly in one direction. It would help to resolve the issue if we had a consistent data set going back over 100 years or more. (Manfred made a similar point.) This of course would mean sitting down with dusty archive records in Russian, Icelandic, Finnish etc and trying to make consistent sense out of them.”
I did that back in 2009 in this article carried here
http://wattsupwiththat.com/2009/06/20/historic-variation-in-arctic-ice/
I am currently working on the period from 1940 backwards to the start of the Hoocene. The melting of the arctic in the 1920-1939 doesnt seem a whole lot different to today, which is one of seven substantial periods of melt we can trace back several thousand years.
tonyb
“will the sea ice decline lead to the AO weakening,”
The temperature diference inside and outside the arctic air is less than used to be weaking jet stream and therefore weather that the Jet stream carries about. On a ‘normal’ June it would be over UK or above Scotland… http://squall.sfsu.edu/gif/jetstream_atl_init_00.gif
currently it’s over Spain http://squall.sfsu.edu/gif/jetstream_atl_init_00.gif
Jet Stream displacement seems to be happening more frequently. I’d say AO is already too weak.
RobertInAz says: June 20, 2012 at 9:43 pm
“What is the basis for this statement? The primary driver of the long-term thinning trend appears to be that thicker multi-year ice has been transported through the Fram Strait”
Dr Meier said
“Winds can also influence the long-term trend in extent. Ogi et al. (2010) estimated that up to 33% of the trend for 1979-2009 could be explained by winds.”
So one might conclude that his educated opinion based on his life work is that wind accounts for 33% of the sea ice loss leaving the rest to increased energy uptake.
You are comparing two different things here, i.e. I am challenging Walt’s assertion as it relates to sea ice thickness/thinning, whereas the quote and paper you’ve cited only addresses sea ice extent, i.e.:
Craig Schleuniger says: June 20, 2012 at 10:17 pm
Remote Sensing Systems (RSS) – Microwave Sounding Units (MSU) – Click the pic to view at source[/caption]
However, your explanation of the many drivers of ice extent relies heavily on the existence of warming temperatures in the Arctic. Yet any references to studies of the number of above freezing hours or higher daily temperatures in the various weather stations in the Arctic are not listed. Would it be possible to get unadjusted temperature references for support?
It has definitely gotten warmer in the Arctic over the last 30 years, i.e. RSS Northern Polar Temperature Lower Troposphere(TLT) Brightness Temperature Anomaly;
[caption id="attachment_54067" align="alignleft" width="568"]
shows a .337 K/C per decade increase.
However, some of this warming may be related to the Arctic Oscillation, i.e.;
versus the change in global temperatures, i.e. RSS Global Temperature Lower Troposphere (TLT) – Brightness Temperature Anomaly- 1979 to Present;
Remote Sensing Systems (RSS) – Microwave Sounding Units (MSU) – Click the pic to view at source[/caption]
[caption id="attachment_54067" align="alignleft" width="568"]
which have only increased by .134 K/C per decade.
Regardless of source of the warming, undoubtedly arctic atmospheric temperatures have increased during the last 30 years. The key question is how much atmospheric warming has influenced the thinning of Arctic sea ice, as compared to wind and currents transporting multi-year sea ice into warmer waters, changes in sea surface temperatures, increases in soot, increased ship traffic and icebreaking, etc.
I am not sure why some people are saying that the Arctic has not warmed. UAH data show a strong warming trend over the Arctic Ocean for their period of record.
http://vortex.nsstc.uah.edu/data/msu/t2lt/uahncdc.lt
Surface warming will, of course, not be the same as that detected by the satellites, but still …
In a previous life I did a lot of rowing when the wind refused to blow. In our Viking long boat we traversed much of the area now rather severely ice bound. The hide covering on our long boat suffered not from ice as we explored the far north and travelled west then south. We turned north again and travelled back to a friendly welcome as the natives we met were a tad aggressive.
It was not long after our exploration that the cold set in and our farmers and communities suffered starvation, as the cold and advancing ice killed crops and live stock. The advent of the sea ice prevented us from fishing and those that could escaped to sea did, it was a bad time.
My question is, what is the problem, in my days the ice was not there, and it was a good time of plenty. WUWT {sarc}
Interesting article. Thanks for posting it Mr. Watts. Seems we were told just a little over 2 weeks ago on this very site that “In fact, as the NSIDC points out, the extent of Arctic sea ice is very close to the average for the last three decades” How quickly things change.
Warm says:
June 21, 2012 at 2:29 am
“I would like to see a bit more about assertion that energy is going into ice melt rather than warming. It’s plausible. And I haven’t encountered it before. But some evidence would be nice. ”
It is widely reported in the litterature. See for instance:
——–
Thanks, but what you have cited is evidence that Arctic temperatures probably would not increase much while ice is melting. Yeah, I’ll buy that. I forget the heat of fusion for water, but it is substantial.
However, what I’m looking for is evidence that additional energy is actually present to melt the ice as well as some thoughts on where that energy is coming from.
Many ice ridges form over winter, with stronger winds, even with the thicker ice. So wind action does not need thin ice alone.
One thing not discussed by Dr. Walt is the role that ocean currents, which over time vary both in intensity and location, has upon the sea ice. Furthermore, the current that flows through the Bearing Strait into the Arctic Ocean is likely affected by the Pacific Decadal Oscillation, and thus has funneled warm water to the arctic since the PDO flipped to the warm state back in the late 70’s.
The heat capacity of water far exceeds that of air and since we know that temperatures during the melt season have varied little over the years, then I find it plausible that ocean currents play a major role in the degree at which ice melts from season to season.
It would seem to me that the winds effect on sea ice would an accelerating effect. If 5 year old ice is blown out of the arctic, it will result in the formation of more new ice, which is more easily moved around and blown out of the arctic as well. Common sense tells you that such a process would result in an acceleration of ice exit through the Fram Strait.
Thicker, older ice will take a much longer period to replace, and its formation itself will be dependent on the wind, and its residency in the arctic over multiple years. IMO, it will take a prolonged period of decreased ice exit through the Fram Strait, thus allowing thicker, less mobil ice to form. I’m not seeing that at the moment in the wind graph on the sea ice page.
It makes sense that the Arctic is warmer, and that ice is therefore melting more quickly. Let’s accept and get past that, to other questions:
1. What is the relative contribution of black carbon, vs. other emissions (CO2, methane, tropospheric ozone)? If people want to reduce warming in the Arctic, black carbon (mainly from older diesels, or newer diesels without the pollution controls diesels now have in the US) can be reduced much more quickly and cheaply than can CO2. The health of people in China would certainly be improved if they reduced diesel emissions.
2. What are the effects of less sea ice in the Arctic? We’ve already learned that the Arctic was largely ice free at summer peak at what used to be called the “Holocene optimum” about 6,000 to 8,000 years ago. We’ve also learned recently that polar bears can swim over 400 miles, and even cubs can swim over 100. The notion that polar bears will die out when there is less ice is now looking more than a little shaky. Even more so when you realize that the last interglacial, 110,000 years ago, was warmer than today, with sea levels 7 feet higher, but polar bears survived that as well.
I take warming seriously, but we need to understand concrete effects, we need to understand timing, and we need to know why we have to act precipitously NOW, putting people out of work and increasing our national indebtedness even more, rather than waiting a decade or so for solar energy to be competitive and with no need for subsidies. When that day comes, CO2 can be dealt with much more easily.
An excellent paper. What I always hope is that when people like Walt seem to have such an excellent grasp on a situation, in this case Arctic sea ice extent, they dont use this knowledge to forecast what will happen in the near future. Canadian Ice Services has, for two years, put in a forecast to ARCUS for minimum Arctic sea ice extent. One wonders why NSIDC is absent from the list of ARCUS forecasters. Surely their knowledge should be second to none, and their forecasts amongst the most accurate.
Hi Walter,
you say:
In your opinion what part does soot have to play in these “increasing temperatures” as you say?
References:
http://www.pnas.org/content/101/2/423.long
http://www.agu.org/pubs/crossref/2005…/2004JD005296.shtml
http://www.sciencedirect.com/science/article/pii/0004698181903437
http://www.sciencedirect.com/science/article/pii/S1352231005002165
http://www.agu.org/pubs/crossref/2010/2009JD013795.shtml
To Jimbo at 7:08 am:
Exactly! Let’s get to the specifics of what is causing the warming, and what reductions can be done quickly and effectively.