| Arctic Ice
In July, rapid melting of sea ice that is less than one year old continued. This ice is the thinnest and thus the most susceptible to warmer conditions. At this stage in the season however, the susceptibility of one-year old and older ice to melt is becoming clear. ~2 million sq. km. of Arctic sea ice melted in July 2010, which wasn't the fastest July melt ever, but still was significant given the overall numbers. ~7 million sq. km. of sea ice remain in the Arctic today.
When you read or hear that most of the warming already experienced by the Earth has happened near the poles and places with high altitude, this is merely one effect that is truly visible on relatively short time frames. Rapid growth and decay of ice on a yearly basis can and will occur. More importantly than areal extent is ice volume, which has dramatically decreased in recent years. As this recently developed time series shows, ice volume has been decreasing for decades, but has really worsened in the past 5 years. It is only recently that enough volume has finally melted that this climate change impact has become obvious in the areal extent of sea ice (by setting record low areal extent).
Antarctic Ice
The state of Antarctic sea ice at the end of July 2010 was as large as it was at the end of June - remaining at much more than climatological normal conditions throughout the month. I haven't read anything definitive as to the reason for this, but given how much Antarctic ice melts and grows each year and taking into consideration the evidence of rapidly decaying and growing Arctic ice, it makes sense that Antarctic sea ice isn't very thick. Nearly all of it melts every year. It further appears as though the rate of growth or decline simply shifts annually with given weather conditions, as we expect.
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Here are my State of the Poles posts from July and June.
Pictures and Graphs
Here is a satellite representation of Arctic sea ice conditions from yesterday:
Compare that with the similar picture from early July:
That's a pretty stunning change in the course of one month. Large regions of 90%+ sea ice concentration has given way to open water (which absorbs heat, instead of reflecting it) and areas of 40%-80% sea ice with melt water on top of it, which does much of the same thing.
Here is the time series graph of Arctic sea ice extent with the +/- 2 standard deviations as a light-gray envelope around the climatological average through yesterday:
You can see in the graph that 2010 extent is hovering near record lows and is clearly far below the 2nd standard deviation area. Furthermore, the extent of 2010 has already fallen below the 1979-2000 mean value. Keep in mind when viewing this time series that there is still over one month of potential melt facing the Arctic. Even if the extent decreases at climatological normal rates, 2010 would rank among the worst on record.
The alternative Arctic sea ice extent time series that I recently found shows conditions since 2002, with different years represented by different colored curves. It provides additional context for comparing current conditions against those from the past. One of the striking things that came through was the record-setting extent of ice in early April 2010 (red curve; the largest areal extent occurring at the latest calendar date on record) shifting to the record-setting low extent of ice in June 2010 and maintaining a 2nd lowest extent on record throughout July 2010. We only have another 6-8 weeks to find out where 2010's final areal extent will land with respect to other recent years.
In a larger context, how do recent years' ice extent compare to IPCC predictions? Well, this is one phenomenon among a growing list that is showing worse conditions than the too-careful IPCC folks were willing to give credence to. What do I mean? Look at Figure 13 of this document (4MB pdf) showing the average and range of September minimum Arctic sea ice extent as projected by models considered by the IPCC. The time series starts in 1900 and runs through 2100. The 20th century projections performed pretty well compared to the observed sea ice extent (denoted by the red line). Sea ice remains as a phenomenon that isn't well understood, so this decent performance is fairly impressive.
But look what happened in the early 21st century (i.e. the last 9 years). The observations fell off to a level that the IPCC models didn't project would be reached until the middle of the century. In other words, the most recent IPCC projections were 40 years too late in projecting the recent record low extents observed in the Arctic!! Note that the models project a gradual decrease in extent down to about 2 million sq. km. by the year 2100. Some glaciologists and climatologists that engage in field activities in the Arctic are now pushing the date at which the minimum plummets below 2 million sq. km., even down to zero-effective extent, all the way back to the next 3-10 years! So not only will most of us witness an ice-free Arctic within our lifetimes (as the IPCC projected 3 years ago), most of use will likely witness an ice-free Arctic within the decade.
You can find the NSIDC's August report here. The page is dynamic, so if you're reading this after August 2010, that month's report will show up first. If that's the case, you can look for the August report on the top pull-down tab on the right-hand side of the page.
Here is a satellite representation of Antarctic sea ice conditions from yesterday:
For comparison purposes, here is the similar picture from July:
Here is the time series graph of Antarctic sea ice extent with the +/- 2 standard deviations through yesterday:
Contrary to Arctic sea ice conditions, the Antarctic sea ice extent has undergone a very large increase since mid-March. As the time-series above demonstrates, today's extent is very unusual (outside the +/- 2 standard deviation range). As I wrote above, however, the rather unusual current Antarctic extent isn't as unusual as the current Arctic conditions. The year-after-year Arctic sea ice loss that has been recorded during the past few years is a result of the warming trend seen in the Arctic over the past 30 years or so. That warmth has accumulated over the Arctic more so than over the Antarctic to date. Without changes to global greenhouse pollution rates, the Antarctic is only biding time until its land-based ice sheet undergoes its own melt scenario.
Cross-posted at WeatherDem - the blog. |
