Tag: sea level

Savaged by a dead sheep #2

Airconcover.jpgIn a meeting last week a late arrival strode in and announced (with a big grin) “You’ve finally made it, Gareth, you’ve been attacked by Ian Wishart.” It appears that my review of Air Con rattled Wishart sufficiently to prompt him to pen an attack on me in his conspiracy magazine Investigate. Over the weekend he helpfully posted what he calls the “salient” bits at his blog under the title More idiocy from the team at Hot Topic. Saves me from having to buy a copy…

Wishart’s main claim is that the evidence I submitted to the ETS Review committee was out of date before it was given, and to prove his point he quotes extensively from his own book. That was a major tactical error on his part, because it gives me an opportunity to demonstrate (once again) that Air Con is full of misrepresentations and inaccuracies.

Continue reading “Savaged by a dead sheep #2”

Weighing up water world

The Ministry for the Environment doesn’t leave local government bodies without advice about sea level rise as a consequence of climate change. I’ve been looking at their guide for local government Preparing for Coastal Change, published last month.  It’s backed by a much longer website document Coastal Hazards and Climate Change rewritten last year by NIWA scientists Doug Ramsay and Rob Bell. The guide is thorough. It points out the impacts of climate change on other physical drivers which would exacerbate the problem of rising sea level.  Storms, storm surge and storm tides, tidal range and high tide frequency, special estuary effects, waves, and the supply of sediment to the coast all add to the likely effects of sea level rise.

Continue reading “Weighing up water world”

A coral room

Coral.jpg Sea level rise is usually considered to be a relatively slow process, at least in human terms. Even a one metre rise over the next century (well within the bounds of possibility) is “only” one cm a year. It seems like a small number, even if when those small numbers start accumulating they bring big problems for coastal communities. Faster rates of rise are known from the past — up to a metre every 20 years during Meltwater Pulse 1A, a 5 metre sea level surge 14,000 years ago, as the great northern ice sheets broke up and the ice age ended. These sorts of rates are not generally considered likely for the near future, because we are in an interglacial and the most vulnerable ice melted a long time ago. However, a paper(*) in Nature this week suggests that a sea level surge of 2 – 3 metres 121,000 years ago, as the last interglacial was drawing to a close, could have taken place in as little as 50 years. Andy Revkin at the New York Times quotes from the study:

“The potential for sustained rapid ice loss and catastrophic sea-level rise in the near future is confirmed by our discovery of sea-level instability” in that period, the authors write.

The NYT is careful to point out that this new information is controversial, and will need confirmation before it’s accepted (see Revkin’s DotEarth blog post), but the most interesting feature of this sudden rise (if confirmed) is that it took place during an interglacial warmer than present, when sea level was higher, and when large parts of the Greenland and West Antarctic ice sheets are thought to have melted. In other words, melting ice sheets are prone to very rapid ice loss. The bounds of what’s possible in our future just took another step outwards.

(*) Rapid sea-level rise and reef back-stepping at the close of the last interglacial highstand, Paul Blanchon, Anton Eisenhauer, Jan Fietzke & Volker Liebetrau, Nature 458, 881-884 (16 April 2009) doi:10.1038/nature07933

[Kate Bush]

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.

Continue reading “We can run, but we can’t hide…”

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.

Andrill.jpg

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.

[Pulp]