Antarctic Sea Ice Melts More Rapdily than the Arctic Sea Ice Each Summer
Why Antarctic Sea Ice Is the Better Climate Change Indicator
by Jim Steele
Arctic vs Antarctic sea ice
1) Sea ice melts deep inside the Arctic Circle during the coldest of winters because warm water from the Atlantic and the Pacific intrude and melt the ice from below. During the past two decades scientists have observed an increase in the volume of warm water penetrating deep inside the Arctic Circle, which then preconditioned the polar ice cap for a greater loss of summer ice.3,8 Changes in the North Atlantic/Arctic Oscillation affect how much heated water is driven into the Arctic, which then causes the widespread melt seen in the Barents Sea and adjoining Kara Sea. Similarly the warm phase of the Pacific Decadal Oscillation drives more warm water through the Bering Strait into the Chukchi Sea.2,5,8
In contrast for millions of years the Antarctic Circumpolar Current (ACC) has created a formidable barrier that prevents any similar warm water intrusions. (The ACC is discussed further at the end of this essay). Therefore changes in Antarctic sea ice are not confounded by warm water intrusions, making Antarctic sea ice a better indicator of the effects of rising CO2 concentrations.
2) Any trend in the degree of summer melt in the Arctic is further confounded by the fluctuating concentrations of thin first year ice. Because continents surround the Arctic Ocean, Arctic Sea ice undergoes cycles of accumulating or reducing the amount of thick, multi-year sea ice that resists melting.2 When the winds pile sea ice against the Arctic shoreline, thicker multi-year ice accumulates. When the winds shift, that thicker ice is blown out past Svalbard into the north Atlantic, and is replaced by thinner, first-year ice that more readily melts each summer. The amount of multi-year ice in the Arctic is controlled by the direction of the winds and the Arctic oscillation.2 It was not warmer air temperatures that removed the thickest Arctic Ice, but sub-freezing winds blowing from the coldest regions in the northern hemisphere.4,5
Due to the constraints of the continents, the maximum extent of Arctic sea ice in 1979 covered about 15 million square kilometers. In contrast, Antarctic sea ice is unconstrained by continental boundaries and each winter winds blowing from the cold Antarctic interior push the sea ice much further towards the equator. By September the sea ice covers 16 to 17 million square kilometers of the Antarctic Ocean, nearly 40% of the southern hemisphere’s ocean surface. Because sea ice is less likely to be piled against a shoreline to form thicker multi?year ice, most of the Antarctic sea ice is relatively thin, first-year ice.
(Measurements of sea ice extent differ depending on what concentration of ice cover is used as the threshold between ice and “no ice”. For example, by using a lower concentration, some authors report that Antarctica’s maximum coverage reaches 20 million km2. Here we use statistics supplied by the University of Illinois’ website The Cryosphere Today to allow an accessible comparison of the Arctic and Antarctic)
Despite more extensive winter ice, each summer Antarctic sea ice retreats much more rapidly than Arctic sea ice. Antarctica’s first-year ice can quickly shrink to a less than two million square kilometers. Even during the Arctic’s “historic” summer lows of 2007 and 2012, the Arctic still retained more sea ice than the Antarctic.
When the Arctic Oscillation shifts and blows thick multi-year ice out into the northern Atlantic, the Arctic is dominated by first year ice that behaves just like the rapidly melting Antarctic sea ice. A season of rapid summer melt is normal wherever first-year ice predominates, whether it occurs in the Arctic or Antarctic, and is not an indicator of rising air temperatures. For example off the coast of Alaska, climate scientists reported a more rapid summer melt even though air temperatures were colder than average, simply because the winds had removed the thicker multi-year ice which was replaced with more rapidly melting first year ice.5
Climate scientists acknowledge that due to Arctic Oscillation’s natural variability, “detection of possible long-term trends induced by greenhouse gas warming [is] most difficult.”3 Therefore because the confounding percentages of trapped multi-year ice fluctuates greatly in the Arctic, trends in Antarctica’s sea ice are again a much cleaner indicator of global climate change.
3) There is so much warm, salty Atlantic and Pacific water lurking just 100 meters below Arctic Ocean’s surface, that it could melt the winter ice completely several times over. As climate scientists noted, “There are arguments in support of an important role for oceanic heat in shaping the Arctic pack ice. They are often keyed to the presence of warm intermediate-depth (150–900 m) water of Atlantic origin”3 Sea ice insulates the ocean surface from the stirring effects of the wind that will raise those warmer waters from intermediate depths. However once the insulating layer of ice is removed, the formation of thicker ice is delayed because the winds will now stir and raise warm subsurface waters. For example even when the Pacific Decadal Oscillation shifted to its cool phase and the volume of intruding Pacific water was reduced, the stirring effect of the winds still caused greater summer melt.6 Global warming advocates argue that the lack of Arctic sea ice amplifies the warming of the Arctic Ocean and accelerates the los of sea ice. They argue without summer ice to reflect the sun, the waters will continue to warm. However if that dynamic was so important, it should be happening in Antarctica as well. But it is not.
4) When the effects of ventilating heat are removed, air temperatures show little warming. Most of the warming in the Arctic has not been caused by CO2-warmed air from above, but from the ventilated warmth from Atlantic and Pacific waters. In addition to raising warmer water from below, thinner ice also allows more heat to ventilate than thicker ice. In fact before the insulating ice cover was blown out of the Arctic, climate scientists in the 1980s and 90s had measured a cooling trend writing, “In particular, we do not observe the large surface warming trends predicted by models; indeed, we detect significant surface cooling trends over the western Arctic Ocean during winter and autumn. This discrepancy suggests that present climate models do not adequately incorporate the physical processes that affect the polar regions.”1
Similarly if we examine winter air temperatures over the South Pole where ventilated heat from the ocean is not a factor, again there is no warming trend (Figure below). In fact there is a slight cooling during the months of April, May, and June which is consistent with the increasing Antarctic sea ice.
5) To explain the growing Antarctic sea ice, CO2 advocates argue that warming is causing more ice. They argue melting glaciers create more freshwater in the Antarctic seas which freezes more readily than salty water. Theoretically that is true, but is deceptive. NASA's Aquarius satellite data clearly shows the Arctic seas contain far more fresh water than in the Antarcitc. Trying to preserve the global warming explanation, advocate scientists offer the schizophrenic explanation that warming is melting ice in the Arctic and expanding ice in the Antarctic, while denying observation. This is irresponsible and only confuses the public's understanding of climate change
A Natural Experiment Has Begun
In 2010 Michael Mann and 8 other climate scientists wrote to Secretary Ken Salazar suggesting climate change had imperiled the polar bears stating, “Scientific studies and observations indicate that climate change is more rapid and pronounced in the Arctic than in other areas of the world. Data and modeling studies repeatedly document that the geography, ice albedo feedback and cloud feedbacks make this region extremely sensitive to climate forcings. The IPCC Fourth Assessment Report (AR4) found that the Arctic has warmed at twice the rate of the rest of the globe on average, and some areas have warmed even faster. Mean annual temperatures in Alaska have increased by 1.9 degrees Celsius in the past 50 years, almost three times the global average over the same time period, and by 3.5 degrees Celsius in winter, as reported by the U.S. Global Change Research Program.” They predicted, “Under current greenhouse gas emissions trends, Arctic summer sea ice has been projected to disappear in the 2030s or before, as reported by several recent studies.”
Oddly, Mann did not address the changes in intruding warm water or the Arctic Oscillation and Pacific Decadal Oscillation (PDO). It was the greater volume of warm water that had passed through the Bering Strait that had caused the extensive loss of sea ice in the Chukchi Sea in 2007 resulting in the historic summer low. But all that is now changing. Mann’ alarming trend of rising Alaskan temperatures has already reversed with the shifting to the PDO cool phase and Alaska is becoming the most rapidly cooling region on the globe, cooling by 1.3°C for just the recent decade.9 As the PDO trends to its cool phase and less Pacific water enters the Chukchi Sea, its sea ice is also recovering.
Likewise the Barents and neighboring Kara Sea are most affected by warm intruding Atlantic water, but as the Arctic Oscillation trends negative, less Atlantic water is pumped towards the poles. The 2013 increase of Kara Sea ice is likely a result. Unlike the Arctic, Antarctic waters are not so affected by cycles of intruding warm water, and its growing sea ice suggests that rising greenhouse gases exert a very trivial effect.
As the Pacific Decadal Oscillation and Arctic Oscillation shift to their cool phases and solar activity wanes, natural climate cycles predict that Arctic sea ice should recover within the next 5 to 15 years. Climate models have demonstrated that Arctic sea ice can recover in just a few years after the winds change.7 Allowing for a lag effect as subsurface heat ventilates and thicker multiyear ice begins to accumulate, recovery could be swift. If so, CO2 advocates like Mann and his allies who have based their political and scientific authority on predictions that Arctic Sea Ice will disappear by 2030 will likely suffer embarrassing unprecedented scientific and political repercussions.
Antarctic Circumpolar Current
Antarctic Circumpolar Current’s (ACC) oceanic barrier was first established when continental drift separated Antarctica from the other continents several million years ago. This allowed an unimpeded flow and the ACC became the world’s greatest and most powerful current, moving a hundred times more water than all the earth’s rivers combined. As it strengthened and isolated the seas inside the ACC, Antarctic waters cooled dramatically. Inside the ACC species requiring warmer water soon became extinct, and the ACC still maintains a formidable thermal barrier that has thwarted invasions by cold-blooded marine species. Since its establishment, true sharks, true crabs, and some families of barnacles are uniquely absent inside the ACC, and many of Antarctica’s remaining cold-blooded species are found nowhere else. In contrast, the Arctic Ocean has been invaded by many North Atlantic and Pacific species that can persist at lower depths in warmer subsurface waters that circulate throughout the entire Arctic. The ACC’s thermal barrier is also why the Antarctic pack ice symmetrically extends far beyond the Antarctic Circle (Figure 1).
1. Kahl, J., et al., (1993) Absence of evidence for greenhouse warming over the Arctic Ocean in the past 40 years. Nature 361, 335 – 337.
2. Venegas, S. A., and L. A. Mysak, 2000: Is there a dominant timescale of natural climate variability in the Arctic? J. Climate, 13, 3412–3434.
3. Polyakov, I., et al., (2010) Arctic Ocean warming contributes to reduced polar ice cap. Journal of Physical. Oceanography, vol. 40, p. 2743–2756. doi: 10.1175/2010JPO4339.
4. 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.
5. 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.
6. Shimada, K. et al. , (2006) Pacific Ocean inflow: Influence on catastrophic reduction of sea ice cover in the Arctic Ocean. Geophysical Research Letters, vol. 33, L08605, doi:10.1029/2005GL025624.
7. Tietsche, S.,et al. (2011) Recovery mechanisms of Arctic summer sea ice. Geophysical Research Letters, vol. 38, L02707, doi:10.1029/2010GL045698.
8. Woodgate, R., et al. (2006) Interannual changes in the Bering Strait fluxes of volume, heat and freshwater between 1991 and 2004. Geophysical Research Letters, vol. 33, L15609, doi:10.1029/2006GL026931
9. Wendler,G., et al. (2012) The First Decade of the New Century: A Cooling Trend for Most of Alaska. The Open Atmospheric Science Journal, 2012, 6, 111-116
10. Landrum, L., et al. (2012) Antarctic Sea Ice Climatology, Variability, and Late Twentieth-Century Change in CCSM4. Journal of Climate, vol. 25, p. 4817?4838.
See related article: Less Arctic Ice Can Be Beneficial
Essay first posted to Watts Up With That as
Why Antarctic Sea Ice Is the Better Climate Change Indicator, guest post by Jim Steele Director emeritus Sierra Nevada Field Campus, San Francisco State University