Deep time, deep water

The last time CO2 hit a sustained level of 400 ppm 15-20 million years ago global average temperatures were 3 – 6ºC warmer than now, and sea level was 25 to 40 m higher, according to research released last week. That’s bad news, because the target for current international negotiations to find a successor to Kyoto is 450 ppm. The finding also provides support for James Hansen’s view that 350 ppm is the maximum “safe level” for CO2 if we want to inhabit a planet with ice at both poles.

Meanwhile, analysis of the Andrill core has discovered a “remarkably warm” period in Antarctica that occurred abruptly 15.7 million years ago, when the McMurdo Sound region could have had January air temperatures of 10ºC and sea temps up to 11.5ºC, according to a new paper in Geology.

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We can run, but we can’t hide…

earthhour.jpg This article appeared in the Perspectives section of The Press yesterday, as part of the paper’s build up up to Earth Hour this weekend. I haven’t seen the letters page today, but I expect the usual suspects will be out in force… 😉

The news isn’t good. Since the Intergovernmental Panel on Climate Change (IPCC) advised two years ago that the evidence for global warming was unequivocal, the pace of change has speeded up. Summer sea ice in the Arctic Ocean has seen a dramatic decline, and in a worrying foretaste of what may be to come, methane — a much more powerful greenhouse gas than carbon dioxide — has been found bubbling out of the ocean floor off Siberia. Down south, analysis of a core drilled into the seabed under the Ross Ice Shelf by a team including scientists from New Zealand (using Kiwi drilling expertise), demonstrates that the West Antarctic Ice Sheet is unstable and likely to collapse if warming continues as we expect over the coming century. Experts are revising their projections of sea level rise upwards with each piece of bad news. A metre or more by the 2090s is now a real possibility.

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This is hardcore

WarmWAIS.jpg The last time that atmospheric CO2 levels were as high as today, the West Antarctic Ice Sheet (WAIS) regularly retreated or collapsed, causing sea level rises of up to 7 metres according to the first analysis of the first ANDRILL core, published in Nature today. The ANDRILL (Antarctic Geological Drilling) programme, a joint effort by scientists from New Zealand, Italy, the USA and Germany, drilled a 1,280 metre core from the seabed under the Ross Ice Shelf. It’s the longest and most complete drill core recovered from Antarctica, and was made possible by drilling technology developed by a team at the Antarctic Research Centre at Victoria University of Wellington led by Alex Pyne.


The two Nature papers [1. Obliquity-paced Pliocene West Antarctic ice sheet oscillations, Naish et al, Nature, 19 March 2009 doi:10.1038/nature07867, and Modelling West Antarctic ice sheet growth and collapse through the past five million years, Pollard and DeConto, doi:10.1038/nature07809] focus on the “warm Pliocene” between two and five million years ago when CO2 levels were around 400 ppm. This is considered a good analogue for where our climate is headed, and the consequence, according to Professor Tim Naish of VUW, joint science head of ANDRILL, is that if we reach 550 ppm CO2 and a resulting 3ºC increase in global temperature, then large parts of the WAIS could melt on timescales of the order of centuries, and be completely gone within a thousand years.

The ANDRILL core documents 38 advances and retreats of the ice sheet, and suggests that during the warm Pliocene the key driver could have been the “obliquity” cycle in the earth’s orbit around the sun — a 40,000 year tilt in the Earth’s axis towards and away from the sun that affects the length of summers at the poles. New modelling of the ice sheet[2. Pollard & DeConto] confirms the link with the obliquity cycle, and suggests that the primary mechanism is melting of the base of the ice sheet by warm oceanic waters — a process that has already started.

In other WAIS news, a British team reports on the success of their robot submarine, Autosub, which made voyages of up to 110km under the Pine Island Glacier ice shelf, recording temperature and salinity, and providing valuable data about melting at the glacier grounding line.

More coverage: Nature commentary by Phillipe Huybrechts, Science Daily, the Telegraph, AP and Reuters.


Reelin’ in the year

IPYWMO.jpg The International Polar Year (IPY) 2007-8 formally draws to a close today, and when today arrives in Geneva there will be a press conference to mark the release of a summary report, The State of Polar Research [PDF], which covers some of the preliminary findings. [BBC report here]. In the run up to this event, there’s been a blizzard (…sorry) of stories from the teams working at both ends of the world, and they make fascinating reading. From huge pools of freshwater building up in the Arctic Ocean to new mountain ranges as big as the Alps under Antarctica, methane plumes off Siberia and the death knell for summer sea ice in the Arctic, there’s a lot to cover…

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Five feet high and rising!

Sea.jpg Yesterday, while dissembling, I had what I might loosely describe as a “bugger” moment. Yale’s Enviroment360 web site (which I plugged on its introduction last June) currently features an interview with Robert Bindschadler, a NASA ice expert who is working on the Pine Island and Thwaites glaciers in West Antarctica. The “bugger” moment?

e360: And in the theoretical case that Pine Island and Thwaites glaciers completely dump into the ocean – obviously it’s not going to happen in the near-future – what kind of sea level rise would they contribute to?

Bindschadler: That portion of West Antarctica, that third that flows northward primarily through those two glaciers, has the potential to raise sea level 1½ meters. That’s sort of an upper bound, a worst case. But the time scale is what really matters. Some say that we won’t see these ice shelves disappear in our lifetime – I’m not so sure. I think we might well.

e360: Are you kidding?

Bindschadler: No, no at all.

Bindschadler looks to be about my age. He reports that the ice shelf is melting from the underneath at a rate of about 50 metres per year at the grounding line. And then, a little later, just to make me spill my tea on the keyboard:

e360: I know that the IPCC was saying maybe 1 ½ feet or a half-meter of sea level rise in the 21st century. Is it your opinion that we could be looking at significantly larger sea level rise?

Bindschadler: Yeah, I think there’s sort of an unspoken consensus in my community that if you want to look at the very largest number in the IPCC report, they said 58 centimeters, so almost two feet by the end of the century. That’s way low, and it’s going to be well over a meter. We may see a meter by the middle of the century.

e360: Oh my gosh.

Bindschadler: And if this behavior that we’re seeing in Pine Island, and even Greenland continues – and we don’t see any reason why it wouldn’t continue – well, over a meter by the end of the century, I think is almost certain.

How notably prim the interviewer is. I think I might have managed something a little more Anglo Saxon. A “meter by the middle of the century” is a very long way above most people’s worst case (though not, perhaps, Hansen’s), but it makes our vulnerability to sea level rise much more of a near-term danger than a comfortable reading of AR4 might suggest. It’s a fascinating article — goes into more detail about the WA ice sheet and PIG (yes, that’s what they call it) than anything else I’ve seen in the last few years. Recommended, but not if you have beachfront property.

Meanwhile, a workshop being held at VUW in Wellington is looking at Andrill results, and finding that the WA ice sheet shows signs of repeated meltbacks over the last five million years [Stuff]:

Professor Tim Naish, director of Victoria University’s Antarctic Research Centre […] is co-science leader of the $30 million Andrill project on the ice, with Professor Ross Powell from Northern Illinois University in the United States.

“Antarctica’s ice sheets have grown and collapsed at least 40 times over the past five million years,” Prof Naish said.

“The story we are telling is around the history and behaviour of the ice sheet … as an analogue for the future,” he said.

Not good news, it seems. Expect a rush of papers covering Andrill work over the next few months.

[Johnny Cash]