A few days ago I used a combination of Arctic sea ice volume data from the University of Washington’s PIOMAS model and NSIDC sea ice extent numbers to project that the Arctic Ocean would be effectively ice-free in late summer within ten years. The key to that exercise was the rate at which the volume of sea ice has been declining — 350 km3 per year over the last 30 years for the full dataset, 410 km3 per year over the last 20, and 740 km3 over the last decade at summer minimum. The rate of volume decline has obviously been increasing. Using those numbers to project ice extent in the future is one thing, but they also tell us something interesting about the overall Arctic heat budget — and we can use that to make a rough guess about when the Arctic will become ice-free year round. The answer is surprising…
Earlier this month the US National Snow & Ice Data Center issued its analysis of this year’s Arctic sea ice minimum — at 4.60 million km2 on September 19, the third lowest extent in the satellite record. However extent (defined here) doesn’t tell you everything about the state of the ice — according to the University of Washington’s PIOMAS ice model 2010 managed to set a new record low for sea ice volume.
In terms of the future of the Arctic sea ice, the volume of ice remaining at minimum is a crucial metric because it represents the size of the heat budget buffer between an ocean with a perennial floating ice cap and one that’s seasonally ice-free. For the Arctic to be ice free in summer, that buffer has to disappear, or become a lot smaller. I’ve been writing about sea ice volume for some time, and considered the overall Arctic heat budget in this post a couple of years ago, so news of the new low volume prompted me to think about what it might mean for the extent metric over the next few years. To do that, I downloaded the NSIDC’s September monthly average extent for the last 21 years, and plotted that against the PIOMAS model’s September average monthly volume (kindly supplied by Jinlun Zhang). Here’s what the data looks like when you plot it on the same chart.
The red line at the bottom, labelled “thickness”, is what you get when you divide volume by extent, and that too has been in decline, reflecting the fact that the loss of volume has been happening faster than the reductions in extent.
I‘m going to be away from my desk for a few days this week, so here’s a few interesting things to read and reflect on. First up: Wellington’s hosting this year’s New Zealand Soil Carbon Conference at Te Papa from Wednesday to Friday. Keynote speakers are Tim Flannery and Christine Jones, and topics to be covered include:
- The science behind climate change and soil carbon
- The on-farm benefits of biological farming
- How research can support innovative farmers
- An overview of the new biological economy and market opportunities
- Practical tips to build soil carbon, humus and soil biology
- Future directions for NZ agriculture and extension services
Full programme here — Friday’s a field trip day. Sounds very worthwhile. If any HT readers are attending (or if the conference organisers are reading this), I’d be very happy to carry a report on events.
Adding to the long list of material debunking standard sceptic & crank claims about climate change, Deutsche Bank’s Climate Change Advisors (DBCCA) have produced a nicely referenced document (PDF), prepared for them by the Earth Centre at Columbia University. Here’s a sample from the executive summary:
Claim: Human society and natural systems have adapted to past climate change.
Response: Past climate changes have often been accompanied by migration, war, and disease. The growing human population will inevitably make environmental change more disruptive in the future, even in the face of increased technological prowess.
A couple of items from Nature News: in Collapse of the ice titans, NN interviews Richard Bates, recently returned from a summer sail along Greenland’s NW coast on the Gambo (more on that voyage at Jason Box’s Meltfactor.org blog) about the melt season at the Petermann and Humboldt glaciers. Ocean conveyor-belt model stirred up looks at a new paper in Nature Geoscience that finds greater than expected variability in the great ocean current network known as the Thermohaline Circulation (THC). Understanding the short term changes in THC flows will be important in attempts to model short term and regional climate change.
The Arctic sea ice looks to be fast approaching its summer minimum, heading for somewhere between 2008 and 2009 — making it the third lowest in the record. Best place to keep up with events is (as it has been all NH summer) Neven’s Arctic Sea Ice blog. The two boats (Northern Passage, Peter 1) attempting to circumnavigate the Arctic Ocean in a single season are both now heading for the southern route of the NW Passage. In the southern Beaufort Sea the Norwegian team are reporting high sea temperatures:
We are still surprised and worried about the high water temperature. At the moment we are registering around 7 to 8 degrees Celsius, which according to the experts is far higher than normal.
Also of interest for sea ice aficionados: a new paper in Quaternary Science Reviews looks at what we know of the history of Arctic sea ice. Coverage at Climate Central and Science Daily but here’s Climate Central talking to the NSIDC’s Mark Serreze:
“They’re telling us that there was maybe no ice during the Arctic summers 7,000 years ago, and also ice-free summers during the last interglacial 125,000 years ago.” Those were due to natural factors, most notably the changes in Earth’s orientation to the Sun that brought more sunlight to the Arctic in summer. This time, says the paper, there is no known natural explanation, and climate skeptics who claim the ice is rebounding after the 2007 low, he says, “are grasping at straws.”
And finally: the British government starts planning to adapt to inevitable warming (but offers no new money). Plus ça change…
Arctic winter sea ice extent reached its maximum on March 31st, the latest date since satellite records began in 1979 according to the latest sea ice update from the National Snow and Ice Data Centre. The maximum extent was 15.25 million square kilometers. The NASA image above shows the ice extent on March 6th, before the late month growth spurt caused by a cold spell in the Bering and Barents seas. This late season ice is unlikely to have much impact on summer minimum, as it is thin and will melt rapidly as temperatures rise. Click on the image to get to a NASA animation of the winter ice season (not available on Youtube, or I would have posted it).
The NSIDC points out that a critical factor is the age and thickness of the ice as it heads into the summer melt season. The video below explains why, and how NASA is running a series of flights over the Arctic, the IceBridge campaign, to replace the thickness data lost with the ending of the first ICEsat mission. A new satellite won’t fly until 2013. The flights are already generating some fascinating imagery — I’ll be keeping an eye on their Twitter feed for more.
The National Snow and Ice Data Centre announced today that this year’s Arctic sea ice minimum extent was likely to have been reached on September 12. It’s the third lowest minimum in the record, behind 2007 and 2008. The image at left shows this year in white, compared with 2007 in darker colours. From the report:
On September 12, 2009 sea ice extent dropped to 5.10 million square kilometers (1.97 million square miles). This appears to have been the lowest point of the year, as sea ice has now begun its annual cycle of growth in response to autumn cooling. The 2009 minimum is the third-lowest recorded since 1979, 580,000 square kilometers (220,000 square miles) above 2008 and 970,000 square kilometers (370,000 square miles) above the record low in 2007. The 2009 minimum is 1.61 million square kilometers (620,000 square miles) below the 1979 to 2000 average minimum and 1.28 million square kilometers (490,000 square miles) below the thirty-year 1979 to 2008 average minimum.
This NSIDC graph gives a very good idea of what’s been happening this year. 2009 has never looked much like beating 2007, but until mid-August it was giving 2008 a run for its money. However, a relatively cool summer and winds during August that dispersed the ice held the minimum extent above last year.
[Update 19/9] NASA’s Earth Observatory posts this graphic of the ice distribution on 12/9:
The usual suspects will no doubt trumpet this as a “recovery”, but the NSIDC team don’t think so: