The state of global polar sea ice area in early August 2012 remains significantly below climatological normal conditions (1979-2009). Arctic sea ice loss is solely responsible for this condition during this boreal summer. Arctic sea ice melted quickly in July because it was thinner than usual and winds helped push ice out of the Arctic where it could melt at lower latitudes; Antarctic sea ice has refrozen at a slightly above normal rate during the austral winter. Polar sea ice recovered from an extensive deficit of -2 million sq. km. area late last year to a +750,000 sq. km. anomaly in March 2012 before falling back to a -1.8 million sq. km. deficit.
After starting the year at a deficit from normal conditions last year, sea ice area spent an unprecedented length of time near the -2 million sq. km. deficit in the modern era in 2011. Generally poor environmental conditions (warm surface temperatures and certain wind patterns) established and maintained this condition, predominantly across the Arctic last year. Conditions were slightly “better” than they were in 2007 or even in 2011 during July. As we know from past experience, that can change rather quickly as Arctic sea ice melts in August and early September on its way to its yearly minimum.
Conditions are prime for another modern-day record sea ice extent minimum to occur in early September. Specific weather conditions over the next month will determine how 2012′s extent minimum ranks compared to the last 33 years. There is a very impressive low pressure system currently in the Arctic Ocean; a strong storm that normally doesn’t occur in July/August. This might seem at first to indicate that sea ice melt might not occur, but the energy being exerted on the ocean and ice is actually more likely to assist in ice melt. This is because of the turbulent motion imparted on the ocean by the storm’s winds, which repeatedly submerge ice in warmer water. The winds also bring warmer sub-surface water up to the surface. After the storm clears and within the following week, we shall see what effects the storm had on the thin Arctic ice. The concentration maps below in particular will take a few days to report the effect – they are five-day averages of measurements so that spurious data do not unduly affect ice condition assessment.
According to the NSIDC, the weather conditions that caused less freezing to occur on the Atlantic side of the Arctic Ocean and more freezing on the Pacific side shifted in late spring/early summer this year to conditions that aided rapid melting across the Arctic – a continuation of similar events in the past six years. Sea ice melt during July was not the fastest on record: 2.97 million sq. km. vs. 3.53 million sq. km. in July 2007! Still, July′s extent was far below average for the month, as some of the graphs below demonstrate. In fact, the extent set multiple daily record lows in July, as shown by one of the graphs below. Arctic sea ice extent on in July averaged 7.94 million sq. km. Ice in the Laptev, East Siberian and Kara Seas remained very much below normal, themselves setting daily record lows during July. The Bering Sea, which saw ice extent growth due to anomalous northerly winds in the late winter/early spring witnessed the record high extent melt back to zero in an extremely short time period earlier this year. The NSIDC included the following in their analysis:
Temperatures at the 925 hPa level (about 3,000 feet above the ocean surface) were typically 1 to 3 degrees Celsius (1.8 to 5.4 degrees Fahrenheit) above the 1981 to 2010 average over the Beaufort Sea and regions to the north, as well as over Baffin Bay. By contrast, temperatures were 1 to 3 degrees Celsius below average over the Norwegian Sea.
In terms of longer, climatological trends, Arctic sea ice extent in July has decreased linearly by 7.1% per decade. This rate is lowest in the spring months and highest in late summer/early fall months. Note that this rate also uses 1979-2000 as the climatological normal. There is no reason to expect this rate to change significantly (more or less negative) any time soon. Additional low ice seasons will continue. Some years will see less decline than other years (like this past year) – but the multi-decadal trend is clear: significantly negative. The specific value for any given month during any given year is, of course, influenced by local and temporary weather conditions. But it has become clearer every year that humans helped establish a new normal in the Arctic with respect to sea ice. This new normal will continue to have far-reaching implications on the weather in the mid-latitudes, where most people live.
Arctic Pictures and Graphs
The following graphic is a satellite representation of Arctic ice as of July 7, 2012:
Figure 1 – UIUC Polar Research Group‘s Northern Hemispheric ice concentration from 20120707.
Compare this with August 6th’s satellite representation, also centered on the North Pole:
Figure 2 – UIUC Polar Research Group‘s Northern Hemispheric ice concentration from 20120806.
The sea ice in the Canadian archipelago and along the northern coast of Russia determine whether the Northwest and Northeast passages open up or not. You can see by comparing the two graphs that the ice is nearly completely melted in the Canadian archipelago. The ice is also mostly melted along the entire northern coast of Russia – just a little remains in the Eastern Siberian sea. Last year, both passages opened again. I continue to think that the Northern Passage will likely open sometime this month. The Northeastern Passage might not open this year, but if it doesn’t, it won’t do so by a thin margin. You can also see in Figure 2 that the dominant wind direction has been toward Greenland. This allows ice to stack up against a landmass and not be exported as quickly out into the Atlantic Ocean where it is likelier to melt. The aforementioned Arctic Ocean storm has shifted wind direction somewhat across the basin, so I don’t expect all of the ice in Figure 2 to remain come September.
Overall, the health of the remaining ice pack is not healthy, as the following graph of Arctic ice volume from the end of July demonstrates:
Figure 3 – PIOMAS Arctic sea ice volume time series through July 2012.
As the graph shows, volume hit another record minimum in June 2012. Moreover, the volume is far, far outside the 2 standard deviation envelope (lighter gray contour surrounding the darker gray contour and blue median value). Figure 3 demonstrates how anomalous conditions are for sea ice in the Arctic. The volume has exceed the -4 standard deviation this year as well as the past two years. I understand that most readers don’t have an excellent handle on statistics, but conditions between -1 and -2 standard deviations are not very common; conditions outside the -2 standard deviation threshold (see the line below the shaded area on the graph above) are incredibly rare: the chances of 3 of them occurring in 3 subsequent years under normal conditions are extraordinarily low. Hence my assessment that “normal” conditions in the Arctic are shifting from what they were in the past few centuries: a new normal is developing. Note further that after conditions returned to near the -1 standard deviation envelope in late 2011/early 2012, as it did in early 2011, volume has once again fallen rapidly outside of the -2 standard deviation area. That means that natural conditions are not the likely cause; rather, another cause is much more likely to be responsible for this behavior.
I found a new graph that shows this and some additional information in a slightly different way:
Figure 4 – PIOMAS Arctic Sea Ice Volume from 1980 through July 2012.
This figure shows volume as a function of date. 2012 is the red curve, which is plotted against the average volume of 2010 through July 2012 (yellow), the average volume of the 2000s (green), the average volume of the 1990s (blue), and the average value of the 1980s (violet). Individuals years from 1979-2011 are indicated by the light gray curves. It is once again clear how anomalous recent conditions are compared to conditions from the latter part of the 20th century. It further shows how rapidly conditions have changed: the volume differences implied by this graph are astounding. The minimum volume typically occurs in early September, which we are approaching again in 2012.
Switching back from volume to area, take a look at July’s areal extent time series data:
Figure 5 – NSIDC Arctic sea ice extent time series through early August 2012.
This is the time series graph that the NSIDC occasionally includes in their monthly reports. I present only this graph and not the graph updated daily throughout the month because of the historical context this graph provides. The ice that piled up in the winter wasn’t thick enough to prevent rapid melt to occur (see early June 2012). The effect of the thickening over the winter on September’s minimum extent will indicate how helpful the early season winds were in building sea ice that doesn’t melt every year back up. Right now, the situation doesn’t look good for September extent. During June, as I wrote above, melting occurred at record rate, resulting in a return to record low extent conditions by the middle of June. 2012′s extent has been below 2007′s for over two months and has been challenging all-time daily record minimums for almost two months. You can also see in this time series graph that conditions since 2007 have clearly differed from the normal conditions established from 1979-2000 (light gray contours surrounding the dark gray mean value).
Figure 6 – NSIDC northern hemisphere sea ice area (not extent) from the past two years only (blue) and the 1979-2008 mean (gray). The red curve shows the anomaly from the mean.
Note in Figure 6 how low the sea ice area is in the beginning of August 2012: -2.157 million sq. km.! Note two additional things. 1) The 2012 area value already is less than the climatological mean value by ~1.5 million sq. km. 2) The 2012 area value is only ~0.5 million sq. km. higher than the minimum recorded in 2011. The area value has slid just slightly under 3 million sq. km. only twice before: 2007 and 2011. Unless weather conditions change radically in the next couple of weeks, 2012 is also very likely to witness another sea ice area value under 3 million sq. km. The link above also shows that sea ice area was lower than 4 million sq. km. only during the past 5 years. Back in the 1980s, the area didn’t fall beneath 5 million sq. km. except for two years (1984, 1989). This is simply another way of noting that the Arctic environment has changed substantially in the past generation. One more note about the anomaly value (-2.157 here): 2007′s lowest anomaly currently ranks as the modern-day record: -3.6 million sq. km. 2012′s anomaly value is obviously far away from that, but has spent the most time below -2 million sq. km. than any year except 2007.
Antarctic Pictures and Graphs
Here is a satellite representation of Antarctic sea ice conditions from July 7th:
Figure 7 – UIUC Polar Research Group‘s Southern Hemispheric ice concentration from 20120707.
Compare that graphic with the same view from August 6th:
Figure 8 – UIUC Polar Research Group‘s Southern Hemispheric ice concentration from 20120806.
Ice gain is less easily visible around the continent than it was a few months ago. As a reminder, the difference between long-term Arctic ice loss and lack of Antarctic ice loss is largely and somewhat confusingly due to the ozone depletion that took place over the southern continent in the 20th century. This depletion has caused a colder southern polar stratosphere than it otherwise would be, reinforcing the polar vortex over the Antarctic Circle. That vortex has helped keep cold, stormy weather in place over Antarctica that might not otherwise would have occurred to the same extent and intensity. As the “ozone hole” continues to recover during this century, the effects of global warming will become more clear in this region, especially if ocean warming continues to melt sea-based Antarctic ice from below. For now, we should perhaps consider the lack of global warming signal due to lack of ozone as relatively fortunate.
Finally, here is the Antarctic sea ice extent time series from August 6th:
Figure 9 – NSIDC Antarctic sea ice extent time series through early August 2012.
Antarctic sea ice extent had remained at or above average to some extent through the late austral fall and through the austral winter, which is good news. The difference in conditions from the first part of 2011 to the similar time period in 2012 is obvious: NSIDC measured last July’s extent near the bottom of the standard deviation envelope while this year’s extent is much healthier.
You can find NSIDC’s August report here.