Tag: glacier

Take a peek at Pukaki’s climate history

Irishmantreambasin.jpg

High in the Ben Ohau range to the west of Lake Pukaki in the South Island’s Mackenzie basin, the glacial moraines in the Irishman Stream Basin (Google Map) are providing important confirmation that the southern hemisphere warmed during a rapid northern hemisphere cooling event at the end of the last ice age. In a new paper in Nature, Glacier retreat in New Zealand during the Younger Dryas stadial Michael Kaplan and a team including three NZ scientists reconstruct the retreat of the glacier that used to fill the basin.

The team dated the sequence of moraines (piles of rock left by the retreating glacier) by measuring the “cosmogenic” beryllium isotope (10Be) in quartz crystals in the rocks — formed by bombardment by cosmic rays — giving a measure of how long the rocks have been exposed to the sky. By modelling the amount of ice in the valley at various moraine positions, they were able to reconstruct the glacier’s decline as the local climate warmed.

Why is this important? Because it’s another important bit of evidence in piecing together the sequence of events as the world warmed up from the last ice age — and in particular because the precise dating confirms that the Younger Dryas cold spell was not global in effect. From the abstract:

Our late-glacial glacier chronology matches climatic trends in Antarctica, Southern Ocean behaviour and variations in atmospheric CO2. The evidence points to a distinct warming of the southern mid-latitude atmosphere during the Younger Dryas and a close coupling between New Zealand’s cryosphere and southern high-latitude climate. These findings support the hypothesis that extensive winter sea ice and curtailed meridional ocean overturning in the North Atlantic led to a strong interhemispheric thermal gradient during late-glacial times, in turn leading to increased upwelling and CO2 release from the Southern Ocean, thereby triggering Southern Hemisphere warming during the northern Younger Dryas.

See also Science Daily. Ref: Kaplan et al. Glacier retreat in New Zealand during the Younger Dryas stadial. Nature (2010) vol. 467 (7312) pp. 194-197

[Edited to correct my original abysmal geography fail – wrong lake in the title]

Don’t watch that, watch this!

If you’ve got any interest at all in the state of the Arctic Sea Ice, resist the temptation to watch the World Cup, or the start of the All Black’s winter season, and take a look at David Barber’s talk at the International Polar Year’s Oslo Science Conference. Go to the “Web TV” page, then scroll through the videos on offer until you see Barber’s talk — On Thin Ice: The Arctic and Climate Change (or use the direct link). Barber’s a good lecturer — he gave yesterday’s (Friday) morning plenary talk at the conference — and he delivers a fascinating overview of his work on the Circumpolar Flaw Project, one of the biggest components of the 2007-8 IPY. Most interesting of all is his description of the state of the sea ice last autumn, as the icebreaker Amundsen went in search of multi-year ice in the Beaufort Sea. He gives a graphic description (involving pyjamas) of the ice breaker discovering that what the Canadian Ice Service maps were suggesting was thick multi-year ice was nothing of the sort — the Amundsen was making a comfortable 13 knots through it, not far short of its top speed of 13.7 knots. That section of his talk starts at about 20 minutes in (by the timer on the player), but it’s worth watching the whole thing. The press release for Barber’s talk is here.

Continue reading “Don’t watch that, watch this!”

It’s grim up North #2

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From NASA’s eyes in the sky, this is a view of the west coast of Greenland downloaded earlier today, looking down on the Ilulissat Icefjord — the outlet for the Jakobshavn Isbrae, the biggest outlet glacier in Greenland and the largest in the northern hemisphere. It’s the long tongue of white reaching up from right of centre to the top of the frame, where you can see the white dots of newly calved icebergs drifting out into Disko Bay (click on the picture to see the 250m/pixel original image at the MODIS site). All very interesting, of course, but I’m posting it to show the numerous large lakes of glacial meltwater that have appeared on top of the ice sheet over recent weeks. At the edge of the ice sheet, the winter snow has melted revealing the greyer ice underneath, but as you climb up the ice away from the coast you get back up into unmelted snow (bottom right). And there are lakes like this a very long way up the west coast, all primed to deliver their water down through moulins to the base of the sheet and thence out to sea, or over the surface in glacial rivers.

I hope this illustrates that there’s more to a melting Arctic than the sea ice — the rest of this post is catching up with sea ice news…

Continue reading “It’s grim up North #2”

Greenland ice melt spreads northwest

This animation shows Greenland’s ice mass loss over 2003 to 2009, estimated by combining data from NASA’s GRACE satellites with high precision GPS measurements of “rebound” in the underlying rock as the weight of ice is removed. The lightest blue shows low levels of mass loss, black the highest. From the University of Colorado press release:

“Our results show that the ice loss, which has been well documented over southern portions of Greenland, is now spreading up along the northwest coast,” said Shfaqat Abbas Khan, lead author on a paper that will appear in Geophysical Research Letters.

Khan goes on to suggest what this might imply for the future:

If this activity in northwest Greenland continues and really accelerates some of the major glaciers in the area — like the Humboldt Glacier and the Peterman Glacier — Greenland’s total ice loss could easily be increased by an additional 50 to 100 cubic kilometers (12 to 24 cubic miles) within a few years.

Another good reason to keep an eye on the Arctic this summer. Climate Progress has a very good overview of recent work on Greenland ice loss and its implications for sea level rise. Well worth a read, if not exactly comforting.

The dangerous sea

This column was published in the Waikato Times on March 16.

The media has paid disproportionate attention to an error in the monumental 2007 report of the Intergovernmental Panel on Climate Change.  In a chapter surveying the possible future impacts of climate change on the Asian region the report included a prediction that the Himalayan glaciers could melt by 2035. The glaciers will certainly melt if we continue on our current course, but not as soon as that. This was a mistake which the IPCC has acknowledged and regretted. Not too bad in a volume of 3000 pages, but a mistake that shouldn’t have occurred and wouldn’t have if procedures had been properly applied.

Since then there have been regular media “revelations” claiming other errors as well. For all the fanfare with which they have been produced these have so far turned out to hinge on little more than minor technicalities. They cause much excitement in the denialist community, but they amount to nothing of consequence.

Overstatement is what the IPCC is being accused of.  But the reality is that its report is generally conservative and cautious and in one very important matter likely to have understated a real danger ahead. That is sea level rise.

 

The IPCC does predict sea level rise in the century ahead, somewhere between 18 and 58 centimetres, depending on how high the level of greenhouse gases is allowed to climb.  It sounds reassuringly manageable.  But this predicted rise comes only from a combination of thermal expansion of the oceans because of warmer temperatures, and the continued slow melting of glacier ice.  It assumes there will be no increase in the rate at which melting has occurred in the great ice sheets of Greenland and the Antarctic.

Time has passed, and it is now widely accepted in scientific circles that there is reason to expect a significant acceleration in the rate at which the Greenland and Antarctica ice sheets lose mass to the sea.  The dynamics of ice movement are beginning to be better understood, and they are not reassuring.  Those massive ice sheets are seemingly not as impervious as once thought and their melting not necessarily a slow predictable linear process. Disintegration may be a more accurate word than melting.

If the IPCC predictions are too cautious, what level of rise is now being considered likely in this century?  One metre say some.  Others say that’s still not allowing sufficiently for the acceleration likely to build, and recommend planning for a two metre rise.  James Hansen of NASA is prepared to consider five metres as a real possibility, though he doesn’t offer that as a prediction..

Of all the predicted impacts of climate change, sea level rise is the one that I find most unnerving.  Its effects on human populations are distressing to contemplate.  The deltaic nations such as Egypt, Vietnam, Bangladesh and Myanmar will be badly hit. Some atoll nations will disappear. Countries with large low-lying coastal plains, such as the US, China and Brazil will be faced with tremendous disruption. Some great cities will be severely threatened, including Miami, New York, Tokyo and Amsterdam. It won’t be all that straightforward in New Zealand for that matter – a one metre sea level rise would put Tamaki Drive under water for example.

And it’s not the kind of damage that can be undone.  How could we get water to return to the ice sheets?  That’s why it is so important that we stop it happening in the first place. Any suggestion that a minor error in the IPCC report has somehow put the urgency of that task into question is out of touch with reality.

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It is likely that this is the last in the series of columns I have been invited to write for the Waikato Times over the past couple of years.  The columns are directed to the general public, not Hot Topic readers, but they may have been useful here in indicating what can be written in public forums. It’s well worth anyone’s effort to get the message across in newspapers.  I often wish there were more scientists writing in that medium, though I know it can be difficult to secure a space for opinion pieces. There are always the letters to the editor, which journalists tell me are popular with readers. The company there can sometimes be embarrassing, but if you’re willing to take that risk a clear statement on climate change will receive wide attention. It has been quite depressing to see in our local paper far more letters (often muddled) from contrarians than from those who take climate change seriously.