Global polar sea ice area in September 2013 was slightly below climatological normal conditions (1979-2008). This represents a change from early 2013 conditions when sea ice area was at or above the average daily value. Antarctic sea ice continues to exist abundantly while Arctic sea ice fell below normal again during the month.
The NSIDC made a very important change to its dataset in June. With more than 30 years’ worth of satellite-era data, they recalculated climatological normals to agree with World Meteorological Organization standards. The new climatological era runs from 1981-2010 (see Figure 6 below). What impacts did this have on their data? The means and standard deviations now encompass the time period of fastest Arctic melt. As a consequence, the 1981-2010 values are much lower than the 1979-2000 values. This is often one of the most challenging conditions to explain to the public. “Normal”, scientifically defined, is often different than “normal” as most people refer to it. U.S. temperature anomalies reported in the past couple of years refer to a similar 1981-2010 “normal period”. Those anomalies are smaller in value than if we compared them to the previous 1971-2000 “normal period”. Thus, temperature anomalies don’t seem to increase as much as they would if scientists referred to the same reference period.
Arctic Sea Ice
According to the NSIDC, September 2013′s average extent was only 5.35 million sq. km., a 1.17 million sq. km. difference from normal conditions. This value is the minimum for 2013 as less sunlight and cooler autumn temperatures now allow for ice to refreeze. September 2013 sea ice extent was 1.72 million square kilometers higher than the previous record low for the month that occurred in 2012. The shift from a record low value one year to a non-record low the next is completely normal. Indeed, had Arctic sea ice extent fallen to a new record low, conditions this year would have been much more inhospitable to sea ice than they were. To be clear, I do not cheer new record lows. They are worthy of discussion not simply because of the record they set, but because they are part of a larger ongoing trend. This year’s minimum extent value did not break that trend, it continued it.
Overall, conditions across the Arctic Ocean this summer prevented record-setting ice loss. There were more clouds in 2013 than 2012. Clouds reflect most incoming solar radiation, which means less sea ice melts. At the end of the melt season, many small seas had normal sea ice extent, which is to say none. Anomalous areas include the East Siberian Sea and the Arctic Basin, which recorded less sea ice extent than normal.
September average sea ice extent for 2013 was the sixth lowest in the satellite record. The 2012 September extent was 32% lower than this year’s extent. The September linear rate of decline is 13.7% per decade relative to the 1981 to 2010 average, as Figure 1 shows. Figure 1 also shows that September 2013′s mean extent ranked sixth lowest on record. You can see from the graph that although a new record minimum was not set in 2013, the negative multi-year trend continued.
Figure 1 – Mean Sea Ice Extent for Septembers: 1979-2013 [NSIDC].
Arctic Pictures and Graphs
The following graphic is a satellite representation of Arctic ice as of July 4, 2013:
Figure 2 – UIUC Polar Research Group‘s Northern Hemispheric ice concentration from 20130704.
The following graphic is a satellite representation of Arctic ice as of October 1st, 2013:
Figure 3 – UIUC Polar Research Group‘s Northern Hemispheric ice concentration from 20131001.
There is more ice on October 1st than there was in mid-September, the date of minimum sea ice extent. That said, you can still clearly see significant melt continued throughout the 2013 summer. Early season melt near the North Pole did not cause widespread loss, as some feared earlier this year. More on that below.
The following graph of Arctic ice volume from the end of September demonstrates the relative decline in ice health with time:
Figure 4 – PIOMAS Arctic sea ice volume time series through September 2013.
This graph shows an interesting development: sea ice volume anomaly did not fall below the 2-standard deviation envelope (light gray) in 2013, the first time in four years that did not take place. Volume anomaly did not increase toward the long-term mean either. This is actually a small amount of good news. While the volume anomaly remains much lower than it was 20 or 30 years ago, it did not set a new record minimum this year. This means thicker ice than this year’s will exist at the start of next year’s melt season. All else equal, this makes it harder for incoming sunlight to melt it completely. All else usually isn’t equal in the real world, however. Next year’s weather conditions could resemble 2007′s rather than 2013′s and push sea ice out of the Arctic faster than normal. But additional volume is a piece of good news for now and we should savor it.
Arctic Sea Ice Extent
Take a look at September’s areal extent time series data:
Figure 5 – NSIDC Arctic sea ice extent time series through early October 2013 compared with five recent years’ data, climatological norm (dark gray line) and +/-2 standard deviation envelope (light gray).
As you can see, this year’s extent (light blue curve) remained at historically low levels throughout the year; it was well below average (thick gray curve), just as it did in the previous five years, to various degrees. Sea ice extent did something different this spring and early summer: the late season surge of ice formation seen in the 2009, 2010, and 2012 curves was not as strong this year; the early summer surge of ice melt seen in the 2010, 2011, and 2012 curves was also not as strong this year. This graph also demonstrates that late-season ice formation surges have little effect on ice extent minima recorded in September each year. The primary reason for this is the lack of ice depth due to previous year ice melt. This year’s extent also did not undergo a rapid collapse, in contrast to years such as 2012 and 2007 (not shown). That said, 2013′s time series remained near the bottom of the 2 standard deviation envelope. Remember, based on this spring’s shift to a new normal period (see Figure 6 below), the bottom of this envelope is lower than last year’s same graph which used the old normal period. As agencies adopt new normals, I think it would be useful to continue showing current conditions against earlier normal periods. That would facilitate comparisons at later dates.
Figure 6 – Graph comparing two climatological normal periods: 1979-2000 (light blue solid line with dark gray shaded envelope) and 1981-2010 (purple solid line with light gray shaded envelope). Also displayed is the Arctic sea ice extent for 2012 (green dashed line) and 2013 (light purple solid line).
This figure demonstrates the effect of adding ten years’ of low sea ice extent data in a data set’s mean and standard deviation values. The 1981-2010 mean is lower than the 1979-2000 mean for all dates but the difference is greatest near the annual minimum extent in mid-September. Likewise, the new standard deviation is much larger than the previous standard deviation. This means that recent variance exceeds the previous period variance. This shows graphically what I’ve written about in these posts: the Arctic entered a new normal within the past 10 years. What awaits us in the future? For starters, scientists expect that the annual minimum extent will nearly reach zero within 30 years. The specific timing of that condition remains up for debate. I think it will happen within the next ten years, rather than thirty years as others predict.
I want to return to a discussion point from this spring. In April, I wrote this: “Many people questioned the overall health of the Arctic ice pack earlier this year when images (like the one below) and video documented extensive cracks in the ice in the Chukchi and Beaufort Seas. A fellow blogger (and new author!) emailed me about this phenomenon and I wrote that I would blog my thoughts on the topic. As Andrew Freedman wrote, “According to the National Snow and Ice Data Center (NSIDC) in Boulder, Colo., this fracturing event was related to a storm that passed over the North Pole on Feb. 8, 2013, creating strong off-shore ice motion. The event is unusual but not unheard of, as there were similar patterns in early 2011 and 2008. However, the NSIDC said the fracturing this time is more extensive.” The worry is the extent and size of the cracks and leads as well as the early calendar date at which they are all appearing – up to weeks before normal.”
Figure 7 – NOAA AVHRR infrared picture of Arctic sea ice on 20130312.
I also wrote this in the same post: “I found this article on the topic and agree with Greg Laden, the author. The cracks and leads might be a big deal or they might not. We will have to wait until the minimum sea ice extent occurs in September before we issue judgment. The scientifically sound course of action would be to wait until early cracks appeared in multiple seasons and then see what the range of response later in the year is. For all we know, the cracks could allow for even more ice to form in March than normal and delay the onset of melting. It strikes me as scientifically unsound and even irresponsible to conjecture about the existence and effect of processes, which we do not understand well. If scientists crow about upcoming devastating Arctic sea ice loss this year and reality doesn’t conform to their wishes, how much credibility with the public do they engender? I think observers should stay patient and discuss the phenomena and effects we do understand – there is plenty of material with which to work!”
Well, a few scientists and a large number of activists crowed about the upcoming devastating Arctic sea ice loss this year. And what happened? September 2013′s minimum sea ice extent value was the 6th lowest on record. Unsurprisingly, there was very little link between March’s ice cracks and September’s minimum value. Activists tend to jump on every latest piece of news and examine it through the same disaster lens. I do not think this is helpful to their cause. To the contrary, I think it actually damages their cause. They lambast skeptics’ out-of-context hysterics, then engage in their own, which opens the door for unneeded skeptics commentary regarding the lack of disaster. To the uninformed observer, the skeptic’s argument makes sense: no disaster occurred, so activist’s arguments must be similarly uninformed and ideological. If activists simply noted the ice crack’s occurrence and waited to see what their effects were, they wouldn’t look foolish today. I did not expect any activists to revisit this episode because they likely view it as a non-event. They likely do not remember today what they screamed about just a few short months ago. Instead, they are looking for the next noteworthy event to shove in everybody’s face as the latest proof of just around-the-corner disaster. Climate change is not like that. It is a wicked problem in large part because it is a slow-moving disaster compared to our lifetimes.
Antarctic Pictures and Graphs
Here is a satellite representation of Antarctic sea ice conditions from July 4, 2013:
Figure 8 – UIUC Polar Research Group‘s Southern Hemispheric ice concentration from 20130704.
And here is the corresponding graphic from October 1, 2013:
Figure 9 – UIUC Polar Research Group‘s Southern Hemispheric ice concentration from 20131001.
October’s figure shows another interesting development: Antarctic sea ice is at a recorded history record maximum. Many people instantly question how Arctic and Antarctic sea ice can exhibit such different behaviors at the same time. The most significant factor is Arctic sea ice exists exclusively over an ocean while Antarctic sea ice extends from a continent. Land and water heat content behaves differently as seasons change. Additionally, there is another human fingerprint on Antarctic weather and climate: the ozone hole, or the ozone depletion that took place over the southern continent in the 20th century. This depletion caused a colder southern polar stratosphere than it otherwise would be. Why? Because ozone heats the air around it after it absorbs UV radiation and re-radiates it to its environment. Will less ozone, there is less stratospheric heating. This process reinforced the polar vortex over the Antarctic Circle. This is almost exactly the opposite dynamical condition than exists over the Arctic. The southern polar vortex has helped keep cold, stormy weather in place over Antarctica that might not otherwise would have occurred to the same extent and intensity. The vortex and associated anomalous high pressure systems moved cold, stable air from over the continent to over the surrounding ocean. This prevented sea ice melt six months ago, so 2013′s sea ice started from a very anomalously high value. It is no surprise then that sea ice ended with a similarly high value.
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 (subs. req’d). The strong Antarctic polar vortex will likely weaken back to a more normal state and anomalous high pressure centers that keep ice flowing into the ocean will not form as often. For now, we should perhaps consider the lack of global warming signal due to lack of ozone as relatively fortunate. In the next few decades, we will have more than enough to contend with from Greenland ice sheet melt. Were we to face a melting West Antarctic Ice Sheet at the same time, we would have to allocate many more resources. Of course, in a few decades, we’re likely to face just such a situation.
Finally, here is the Antarctic sea ice extent time series through early October:
Figure 10 – NSIDC Antarctic sea ice extent time series through early October 2013.
The 2013 time series continues to track near the top of the +2 standard deviation envelope and above the 2012 time series. Unlike the Arctic however, there is no clear long-term trend toward higher or lower sea ice extent conditions in the Antarctic Ocean. These conditions are a relatively new feature of the Southern Hemisphere.
Given the lack of climate policy development at a national or international level to date, Arctic conditions will likely continue to deteriorate for the foreseeable future. This is especially true when you consider that climate effects today are largely due to greenhouse gas concentrations from 30 years ago. It takes a long time for the additional radiative forcing to make its way through the climate system. The Arctic Ocean will soak up additional energy (heat) from the Sun due to lack of reflective sea ice each summer. Additional energy in the climate system creates cascading and nonlinear effects throughout the system. For instance, excess energy pushes the Arctic Oscillation to a more negative phase, which allows anomalously cold air to pour south over Northern Hemisphere land masses while warm air moves over the Arctic during the winter. This in turn impacts weather patterns throughout the year across the mid-latitudes and prevents rapid ice growth where we want it.
More worrisome for the long-term is the heat that impacts land-based ice. As glaciers and ice sheets melt, sea-level rise occurs. Beyond the increasing rate of sea-level rise due to thermal expansion (excess energy, see above), storms have more water to push onshore as they move along coastlines. We can continue to react to these developments as we’ve mostly done so far and allocate billions of dollars in relief funds because of all the human infrastructure lining our coasts. Or we can be proactive, minimize future global effects, and reduce societal costs. The choice remains ours.