found at RC recently

http://www.agu.org/pubs/crossref/2007/2006GL028385.shtml

Propagation of water-filled crevasses through glaciers is investigated based on the linear elastic fracture mechanics approach. A crevasse will penetrate to the depth where the stress intensity factor at the crevasse tip equals the fracture toughness of glacier ice. A crevasse subjected to inflow of water will continue to propagate downward with the propagation speed controlled primarily by the rate of water injection. While the far-field tensile stress and fracture toughness determine where crevasses can form, once initiated, the rate of water-driven crevasse propagation is nearly independent of these two parameters. Thus, rapid transfer of surface meltwater to the bed of a cold glacier requires abundant ponding at the surface to initiate and sustain full thickness fracturing before refreezing occurs.

—- quoting —-

“… This unexpected result shows that the Rutford Ice stream (larger than Holland) varies its speed by as much as 20% every two weeks. Ice streams – and the speed at which they flow – influence global sea level. Understanding their behaviour has been a priority for some time. On average the Rutford Ice Stream moves forward by one metre every day.

Reporting this week in the journal Nature, British Antarctic Survey (BAS) glaciologist Hilmar Gudmundsson says,

‘We’ve never seen anything like this before. The discovery that the spring-neap tidal cycle exerts such a strong influence on an ice stream tens of kilometres away is a total surprise. For such a large mass of ice to respond to ocean tides like this illustrates how sensitively the Antarctic Ice Sheet reacts to environmental changes. Glaciologists need now to rethink how the Antarctic Ice Sheets reacts to external forces. ‘

The variations in flow of the Rutford Ice Stream are related to the vertical motion of the ocean caused by the gravitational effects of the sun and moon. Every two weeks sees large tides, the so-called spring tides which are followed by small tides, the neap tides. Scientists expect movement of the floating ice shelves, but the Rutford Ice Stream is grounded in the shallow waters of the Antarctic continental shelf.
—- end quote—-

Tides affect speed of Antarctic ice slide
Reuters – Dec 20, 2006

OSLO (Reuters) – Tides affect the speed at which an Antarctic ice sheet bigger than the Netherlands is sliding toward the sea, adding a surprise piece to a puzzle about ocean levels and global warming, a study showed on Wednesday.

The Rutford Ice Stream of western Antarctica slips about a meter (3 ft) a day toward the sea but the rate varies 20 percent in tandem with two-week tidal cycles, it said. And the effect is felt even on ice more than 40 km (25 miles) inland.

“We’ve known that (twice-daily) tides affect the motion of ice streams but we didn’t know it happened on this two-weekly time scale,” said Hilmar Gudmundsson, an Icelandic glaciologist at the British Antarctic Survey.

…

“For such a large mass of ice to respond to ocean tides like this illustrates how sensitively the Antarctic Ice Sheet reacts to environmental changes,” he said of a report published in the scientific journal Nature…..

Thanks. Assume that US action motivates a 20% decrease in total global emissions. Under the assumptions presented above this would reduce the increase in global sea level rise in 2100 by 1.4 inches. For every addition 10% decrease in emissions, simply add another 0.7 inches.

The other aspect to the question I wanted to raise is whether, if as a result of serious regulatory actions on the part of the EPA other countries were to follow with stronger efforts at emission controls than they would have otherwise undertaken, there might be something of a “multiplier” effect that’s not considered in the model of the effects EPA regulations upon which you based your calculations, and that the impact of such a dynamic could lead to greater impact on sea level change by EPA regs than those suggested in the calculations.

This is of course conjecture, and indeed a sort of thought experiment, but I would think it’s a relevant consideration given that such a dynamic has been an underlying principle of global action on AGW, and given that we are dealing with a situation that is currently marked by significant areas of uncertainty.

Best,
MB

These are good questions:

“is it morally justifiable to keep on worrying about CO2, and when should we be focusing our attention and resources on more important matters? It seems kinda silly to be taking drastic and expensive measures to combat a bearly noticable threat 50 years in the future when millions of people are dying from AIDS, malaria, starvation, war, etc. Seems to me that we need to get our priorities straight.”

I would simply observe that the problems that those in the developed nations are most concerned about are quite naturally those that they view as most directly affecting their own interests, including the interests of their children. That may explain why the discussion tends to focus on mitigation rather than adaptation.

Adaptation in the developed world will occur throughout the private economy without much government involvement, but mitigation requires international coordination. This is why the climate change worriers largely focus on mitigation.

I submit that those who profess to be most interested in the welfare of the developing world and who insist that we adopt no government-mandated mitigation measures are largely apologists for those who benefit most from using the atmosphere as a GHG dump; they, too, probably have no real appetite for the difficult and expensive task of using domestic tax dollars in a coordinated effort to help poorer countries to develop and to adapt to looming climate change.

In other words, self-interest rules.

1. You write, “. . .in a response to Chris Giovinazzo on Nov 30 I think, you argued, although admitting that it was somewhat silly, that someone suing EPA to regulate human breathing as a cause of global warming, would or should win on standing. This means, at least implicitly, that you think . . .”

No. I was simply applying Chris’ criteria to see if I understood what he meant. I was not advocating a general or specific principle for legal standing.

2. Your response misses the point about the Kyoto/forest debate, which begins by acknowledging that perturbations to forests have an effect. The debate is about whether afforestation should count as an emissions offset. Some poeple say no since it does not get to the causes of global warming (i.e., fossil fuel burning).

3. You write — “I am not saying that policies couldn’t be constructed to add carbon cycle flows up in various ways, of course they can.”

Good. After I cancel out the double negatives I think then we are in 100% agreement!

4. We agree then.

Thanks!

(Feel free to have the last word on this exchange if you’d like. I’m done for now;-)