The state of global polar sea ice area in early July 2012 has once again fallen significantly below climatological normal conditions (1979-2009). Arctic sea ice loss is solely responsible for this change in condition since last month. Arctic sea ice melted quickly in June 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 near normal rate during the late austral autumn and early 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. The last time global sea ice area remained near 19 million sq. km. through May was in 2007, when the Arctic extent hit its modern day record minimum. The maximum in the boreal spring the past two years was ~19.5 million sq. km.
Conditions are prime for another modern-day record sea ice extent minimum to occur in September. Specific weather conditions over the next two months will determine how 2012’s extent minimum ranks compared to the last 33 years.
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 June was the fastest on record: 2.86 million sq. km.! As such, June′s extent was far below average for the month. In fact, the extent set multiple daily record lows in June, as one of the graphs below will show. Arctic sea ice extent on in June averaged 10.97 million sq. km. Barents and Kara Sea ice remained very much below normal, themselves setting daily record lows during June. Additional areas, such as the Hudson Bay and the Laptev Sea are also now experiencing anomalously low extent conditions. 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. Overall, near surface temperatures were warmer than average (by 1.8 to 7.2F at the 925hPa level) across the Arctic Ocean.
In terms of longer, climatological trends, Arctic sea ice extent in June has decreased by 3.7% 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: 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 June 7, 2012:
Figure 1 – UIUC Polar Research Group‘s Northern Hemispheric ice concentration from 20120607.
Compare this with July 7th’s satellite representation, also centered on the North Pole:
Figure 2 – UIUC Polar Research Group‘s Northern Hemispheric ice concentration from 20120707.
The sea ice in the Bering Sea, as mentioned above, completely melted due to the ice’s young age and thin depth. What remained missing last winter and early spring was the sea ice north of Scandinavia. This is the result of anomalously warm waters from the Gulf Stream being drawn further north than is normal. This is due to the positive AO index & NAO index during the last boreal winter and spring. As a side note, this phenomenon combined with the most recent, moderate La Niña in the Pacific Ocean has led to Dec-Jun being anomalously warm and dry for most of the U.S. Indeed, this year has been the warmest Jan-Jun period on record in the US, as I will detail in a separate post. These conditions were joined by anomalously warm conditions along the Arctic coast on three continents. Those conditions helped melt the ice near the coast more rapidly than is normal.
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. Last year, both passages opened again. What will happen in 2012? Given today’s information, I would venture a guess that they will be open.
Overall, the health of the remaining ice pack is not healthy, as the following graph of Arctic ice volume from the end of June demonstrates:
Figure 3 – PIOMAS Arctic sea ice volume time series through May 2012.
As the graph shows, volume hit another record minimum in June. Moreover, the volume is far, far outside the 2 standard deviation envelope (lighter gray contour surrounding the darker gray contour and blue median value). I understand that most readers don’t have an excellent handle on statistics, but conditions between -1 and -2 standard deviations are rare and 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.
Switching back from volume to area, take a look at June’s areal extent time series data:
Figure 4 – NSIDC Arctic sea ice extent time series through early July 2012.
As you can see, the extent in April briefly matched average conditions before a relatively warm spell melted ice quickly in mid-April. The ice that piled up in the winter wasn’t thick enough to prevent rapid melt to occur. 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, things don’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 about one month now. In fact, the melt of early June began the day after I posted my last State of the Poles post.
Occasionally, I also like to include a supplemental time series graph that the NSIDC report contains. Here is this month’s supplemental graph:
Figure 5 – NSIDC Arctic sea ice extent time series of ice extent conditions comparing previous years’ data and 2012 data through June.
This graph contains all of the same data as the previous graph and adds the time series lines from the previous 4 years. As you can see, extent varies during the same month from year to year. The recent record decline in extent, caused laregly by a change in wind direction and speed, has reduced Arctic ice extent back to ~11 million sq. km., which is far below normal for June. The past two years also saw somewhat similar reductions through June, although the starting values were obviously different. Despite these differences in subsequent years, the minimum ice extent values were quite similar: at or near the record daily lows set in 2010. Will fall 2012 be any different or will the surge in ice growth on the Pacific side of the Arctic help to stave off the worst effects seen in the past five years?
Antarctic Pictures and Graphs
Here is a satellite representation of Antarctic sea ice conditions from June 7th:
Figure 6 – UIUC Polar Research Group‘s Southern Hemispheric ice concentration from 20120607.
Compare that graphic with the same view from July 7th:
Figure 7 – UIUC Polar Research Group‘s Southern Hemispheric ice concentration from 20120707.
Ice gain is less easily visible around the continent than it was the past couple of months. 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 July 7th:
Figure 8 – NSIDC Antarctic sea ice extent time series through early July 2012.
Antarctic sea ice extent had remained at or above average to some extent through the austral fall and early 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 year’s extent near the bottom of the standard deviation envelope while this year’s extent is much healthier. Despite the shift in preceding conditions, extent in June 2012.
You can find NSIDC’s July report here.