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Sunday, October 09, 2005

New satellite to measure something not included in warming models

Last week the topic of polar ice melting was brought up. One of the issues that was most important was the probelm of models versus real life, because most of the reports discussed expected ice melting from modelling of "global warming". While it wasn't quantified it appeared that most of the models were somewhat light on the real world parameters, ie they didn't include many significant factors. A BBC report about the coming launch of the European Space Agency's launch of their new Cryosat satellite is interesting in indicating how little is known in some areas of the modelling. The satellite is going to fly a three year mission to actually measure Arctic ice thickness directly, although three years is a short time and cycles longer than a couple of years won't be evident it will do what isn't done now.

If you read around the obligatory blurb about threats to the world and so on, which permeate articles like this and distract from the real issues, then this is interesting
Data from the US space agency (Nasa) and European Space Agency (Esa) satellites (Envisat, ERS) gives the most accurate record of changes in ice cover.

But the orbits of these satellites, which are designed to study the whole of the planet, leave vast areas uncharted, in particular the nine degrees of latitude nearest the poles. Historical records suggest that this sector may be subject to the greatest thinning.

Climate models predict what may happen to ice as the planet warms. These rely on a number of assumptions - if ice melts, the ocean will become warmer, as there will be less ice to reflect radiation back into space. Scientists need hard data to feed into the models to firm up their predictions.
Huge tracts of Arctic and Antarctic ice are uncharted, areas expected to be of most significance are not studied in any detail. The models on which predictions are made are reliant on assumptions, but these are poorly tested by the lack of real information. Remarkably one of the most important predictions, ice thinning, is not directly measurable in a meaningful way. The Cryosat is intended to help that by actually doing the measurements, being able to determine altitudes to millimeter precision over an area of about a kilometre wide. The ESA web page describes the mission in more detail. For instance, the rationale for the new satellite is
The generation of radar altimeters currently flying on satellites including ERS-2 and Envisat have made a large contribution to our knowledge of the mass balance of Greenland and Antarctic ice sheets, but they cannot return reliable data from the ice edge, where the rate of change is greatest. Similarly, over the ocean their resolution is insufficient to detect the majority of individual pack ice pieces. The design of CryoSat's new SAR Interferometric Radar Altimeter (SIRAL) has been optimised to close these data gaps.
The current generation of survey satellites can't measure very well the very areas of most importance in this work.
"Back then, analysis of this data suggested that a significant – up to 40% - thinning had occurred since the 1960s, with the largest thinning around the pole. The big question is whether that thinning has reversed or continued as we have entered the new century."

"That question has gained even more impetus since the news that the extent of summer ice in the Arctic has reached a record minimum this year. But has it also thinned? That's the crucial question to which CryoSat will provide the answer."
While the ice has been retreating in summers, no one actually knows if it is also thinning, which is crucial in the debate. If it isn't thinning much then "global warming" is not a large factor since retreating edges would be caused by sea currents. Here is another nugget
"As a scientist I am interested in using CryoSat data for validating our sea ice models, and combining the data with other met-ocean data to better understand the variability of sea ice thickness," Haas explains. "We also want to assimilate sea ice thickness into our models."
Sea ice thickness is not currently modelled, this is just one of the reasons to take "models" with a grain of salt. If you don't know what is included, excluded and assumed then it is very hard to rely on their predictions. Or this may be the most telling quote
"Despite all available measurements of snow accumulation, ice velocity, surface and basal melting and iceberg discharge, it is still not known for certain even whether the ice sheet is growing or shrinking." CryoSat should remedy this state of affairs.
With all current knowledge the actual state of the ice sheets is unknown, pretty much all the modelling is speculation at this point.

Reading press releases from scientific groups about this or that measurement of an ice field indicating the imminent flooding of a city is pretty much an exercise in fiction. It is important to remember that models are not scientific theories, they do not hold the same status and pretty much all models will eventually be found wanting in critical aspects. The current state of knowledge is quite poor, in relation to the policies and massive actions being proposed to deter the results of some modelling. Improved data collection helps improve modelling, but even that cannot make the existing models account for longer term cycles that are neglected in the models. The three year Cryosat mission will tell us what is happening now, but it won't be able to say anything about decadal or century long cycles (they will appear as trends). What it does do is improve a section of the puzzle.
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The satellite crashed.

Posted by Chefen | 10/09/2005 03:11:00 am


Anonymous Anonymous said...

Actually satellite measurement has shown that the Antartic ice cover is thickening over the bulk of the continent. The only exception being the Antartic peninsular (which lies outside the Antartic circle).

Naturally the Nature article that reported this quoted a Global Warmer who claimed that GCMS predicted this very result. Increased warmth leads to increased evapouration leads to increased precipition bla bla

Here is the BBC's take on this

All of which begs the question if Global Warming causes the Antartic Ice cover to increase why doesn't it do the same in the Northern Hemisphere?

Incidentally the team which made the discovery made no claims either way with regard to Global Warming despite what the linked BBC article says. Nature found a Global Warmer to comment on the results (not a member of the team) and the BBC, surprise surprise, has got it wrong

10/09/2005 06:48:00 am  
Blogger Chefen said...

Yep, BBC and other reports are generally a confused mishmash of various opinions and speculations largely based on modelling. It is little wonder no one has a coherent understanding of the whole issue, it's only by going to the original sources you can find the limitations and qualifications discussed. Interestingly that BBC article you cite discusses Cryosat at the end, as giving better measurements "next year" that is, now).

10/09/2005 07:03:00 am  
Anonymous Anonymous said...

Bad luck, it crashed. No more satellite.

10/09/2005 08:33:00 pm  
Blogger Chefen said...

Ah well, at least it was cheap. But the points remain.

10/09/2005 09:12:00 pm  

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