| Arctic Ice
The big change since last month has been the continuation of very rapid melting of ice that is less than one year old. This ice is the thinnest and thus the most susceptible to warmer conditions. In fact, as of the beginning of July 2010, the areal ice extent reached a modern-day record low of ~9 million sq. km., which is 2 million sq. km. below the climatological average! Unfortunately, ~2 million sq. km. of Arctic sea ice melted in June 2010. When you read or hear that most of the warming already experienced by the Earth has happened near the poles, this is merely one effect. 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.
Antarctic Ice
The state of Antarctic sea ice in July 2010 was much better than it was during June 2010 - exceeding the average extent relative to climatological norms by an increasing margin throughout the last month. The areal extent shifted from normal to significantly more than normal during this time. The extent at the middle of July 2010 was larger than at the middle of July 2009. I haven't read anything definitive as to the reason, 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 appears as though the rate of growth or decline simply shifts annually with given weather conditions.
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Here are my State of the Poles posts from June and May.
Pictures and Graphs
Here is a satellite representation of Arctic sea ice conditions from a couple days ago (no image for yesterday is yet available):
For comparison purposes, here is the similar picture from June (just a couple of weeks ago):
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:
I was recently made aware of a slightly different Arctic sea ice extent time series - one that shows conditions since 2002, with different years represented by different colored curves. I have found that it provides additional context for comparing current conditions against 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 extent occurring at the latest calendar date) shifting to the record-setting extent of ice in June 2010. While the rapid melting observed so far this year is significant, it doesn't really indicate one way or the other what conditions this fall will be. 2007 (dark green curve) and 2008 (light green curve) witnessed very low extents. Will weather and ice conditions be conducive to repeat that sad state this September? We'll have to wait and see.
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 this graph 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 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 0-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 July report here. The page is dynamic, so if you're reading this after July 2010, that month's report will show up first. If that's the case, you can look for the June 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 a couple of days ago (no images from yesterday are yet available):
For comparison purposes, here is the similar picture from June:
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). It is impossible to tell how much ice will be present in mid-September when its extent is highest for this year.
Cross-posted at WeatherDem - the blog. |
