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)
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Dr Meier, Hopefully, since you will be responding to this thread there is a question about a comment you made in a 2008 CNN interview that was hyping shrinking ice and polar bear cannibalism, that has long troubled me. You said, “That warming is going to spread to the lower latitudes, to the United States, and it’s going to affect storm systems and storm tracks, the jet stream; that’s going to affect crops and all sorts of things,”
My understanding is excess heat from the tropics is redistributed towards the poles due to the temperature gradient. Your suggestion that heat will accumulate in the poles and then flow back towards the equator against that gradient appears to defy the law of physics. Polar air masses that move south are always colder. So could you explain why a scientist would suggest such a thing?.
I’m confused, as usual. I was under the impression the models predict the poles cool down and the tropics warm up due to global warming (err, Climate change).
Please help me to understand this, and if the poles are supposed to cool down, then you have to take away the idea it’s on account of heat, as you are saying here.
Or do you think the models are wrong? Or do you think there is less ice when things cool down?
Really in a spin,
Regards,
Ed
Has anyone ever succeeded in definitively mapping thickness across the entire broad swath of Arctic Sea Ice and done so in a way to create meanigful time series of such mappings? And the follow on question, what would be the earliest reliable baseline mapping assuming any acceptable mapping even exists or has ever existed?
Ed Barbar,
Climate models predict that there will be more warming at the poles than at tropical latitudes.
Just The Facts says
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;
Thanks for the point out. I do understand that both you and myself can find a source or two for a short period arctic temperature trend. However, I was looking for the reason that Dr Meier did not list a reference for temperature data and it’s effect on ice melt.
@Jimbo
“Water temperature and salinity
Maximum upper ocean temperatures in summer 2009 continued to decline since the historical extreme in summer 2007 (Fig. O.2). This tendency is strongly linked to changes in the characteristics (e.g., pace and location) of the summer sea ice retreat and their effect on local atmospheric warming (Steele et al. 2010, manuscript submitted to J. Geophys. Res.). Surface warming and sea ice reduction in the Canada Basin has also been accompanied by the widespread appearance of a near-surface temperature maximum at 25–35 m depth due to penetrating solar radiation (Jackson et al. 2010). As described in the Arctic atmosphere section, the heat accumulated in the surface and near-surface layers of the ocean can be released back into the atmosphere in the fall—a cycle that is likely to influence sea ice conditions in the future.
”
Extract from the link I posted earlier.
@Jimbo
http://www.eea.europa.eu/themes/coast_sea/sea-surface-temperature/rising-temp
More evidence for you.
Any author who knows the difference between complementary and complimentary registers confidence in me. Well done Dr Meier
Dr. Meier: Thank you for posting. That said, I have a difficult time reading your science, well prepared and articulate presentation, and accepting your leaps in logic. The leaps in logic are either based on somebody else’s science (and I assume their conclusions) or behind paywalled research and again their conclusions.
Unexplained, yet explained away by possibles assumption. That is, plausible conclusions are maybe used as conclusions and citations to the work drop the maybes. No long term historical research, No existing climate or circulation cycles verified, no defined laboratory experiments/tests confirming assumptions then verified by direct observations of the identified processes in the field. It seems that climate science no longer is based on repeatable tests confirmed by larger yet still repeatable experiments in the field.
When people fantasize theories and then confirm them with programs and models designed to provide confirmation, it bears little difference both in result and method from preschoolers involved in make-believe plays. Nothing of this process resembles reality except through sheer chance.
Your science is excellent. Keep performing your science and expect others in the climate science world to perform with equal rigor and standards. When faced with a leap in logic, look explicitly for the data that validates and confirms the steps towards the conclusion. All too often we are being handed conclusions and refused any information that might prove a supposition.
Coincidence is not causation! Yet we are being handed conclusions that depend on accepting causes without proof that current trend are more than coincidence. A science lesson every climate scientist existing must understand is that climate is based on natural cycles (often very long ones)until PROVED otherwise. Your science is wonderful. Your acceptance of other’s statements of causation when proof is lacking is puzzling. What about climate science is so secret that you accept their proofs, but we are not allowed to see/read/analyze those proofs. Are we so unclean?
Think about it. If you were to look at long long climate cycles and you accept there are ice ages and warmer periods in-between, what are your expectations for how this cycle proceeds? Just what steps have you taken to ensure any atmospheric science you observe are truly outside of normal boundaries? This is even before we get into historical concepts of warmer or cooler episodes of climate, e.g. Roman warm period, medieval warm period. And we haven’t even reached back to deeper time climate cycles, yet; such as, when can we expect a return to weather the dinosaurs experienced? If not, exactly whynot? I’ll lay odds that it’s not because of CO2 or CFCs, (CFCs have been postulated recently by warmers trying to explain why CO2 is on vacation as a greenhouse gas the last decade).
“Using all different ranges of greenhouse gasses that occurred during the early Eocene, models were unable to produce the warming that was found at the poles and the reduced seasonality that occurs with winters at the poles being substantially warmer. The models, while accurately predicting the tropics, tend to produce significantly cooler temperatures of up to 20 °C (36 °F) underneath the actual determined temperature at the poles.[14] This error has been classified as the “equable climate problem”. To solve this problem, the solution would involve finding a process to warm the poles without warming the tropics. Some hypotheses and tests in attempt to find the process are below.”
http://en.wikipedia.org/wiki/Eocene
John Daly gave a good reason to take Atlantic and Pacific ocean circulation into consideration.
After all, more floating ice melts from the bottom than from the top. Here is one of his illustrations
Seems to me, Dr Meier falls a bit short in acknowledging the influence of the respective oceanic oscillations.
I prefer to look at all sources of additional heat energy. Greenhouse gas sourced higher air temperatures are one source, but a distant cousin compared to what really has the power to warm us or chill us. The author has failed to rule out the first encountered pathology – Oceanic current temperatures going in and out of the bowl. In NE Oregon, we are hog-tied to the temperature of the pond to the west of us. And not just the overall temperature, but the temperature and placement of different pools of warm versus cold water in that big pond. As the on-shore flow and jet stream pick up these “pond” signals we get warm and dry, warm and wet, cold and dry, or cold and wet, depending on where these ponds are and what temperature they are. What’s worse, we get to experience these wonderful results over multiple years, because the offending pools of water tend to oscillate noisily in and out of these conditions over multiple years and sometimes over multiple decades.
The Arctic is filled with currents going this way and that, and run the gamut of temperatures. This also means the Arctic has its fair share of pools. It makes sense to see what is happening with these current and pool temperatures before looking at CO2. The proper analysis should have included such an obvious and well known source and store of heat energy variations, oscillations, and trends.
If you take a look at the warming trends in the NH air temperature outside of the arctic (eg 0oN-60oN) you’ll see that there has been zero warming over the past decade.
There has also been zero warming in the Atlantic waters entering into the arctic seas for the past 5 years.
How long can internal feedback processes continue to warm the arctic and melt more ice without an increase in energy avected from outside the arctic?