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Weighing change in Antarctica

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Guest commentary by Matt King, Michael Bentley and Pippa Whitehouse

Determining whether polar ice sheets are shrinking or growing, and what their contribution is to changes in sea level, has motivated polar scientists for decades. Genuine progress began in the early 1990s when satellite observations started to provide (nearly) spatially comprehensive sets of observations. Three very different, and hence complementary, approaches are now employed, although each has a particular limitation:

  • Satellite altimetry: measurements of ice sheet volume changes from laser or radar altimeters (e.g. IceSat) can be converted to mass changes through correction of spatially- and temporally-varying surface density together with spatial extrapolation to unsampled regions. The main limitation lies in the models used to correct for surface density changes.
  • Input-minus-output: calculating the difference between the mass of snow accumulated and that of the ice (and meltwater) being discharged gives the mass imbalance. The snow accumulation is normally estimated from numerical models and the discharge is computed using the multiple of measured velocity at the edge of the ice sheet with its measured or inferred ice thickness and density. Thus, uncertainty in accumulation models and sub-glacial topography at the grounding line propagate into mass balance uncertainties.
  • Satellite gravimetry: changes in Earth’s gravity field can be measured from satellite (e.g. from Gravity Recovery and Climate Experiment, GRACE) and used to determine changes in ice mass but only after accounting for mass-change effects that are not due to ice mass redistribution – in particular the glacial isostatic adjustment (GIA).

Our recently published Nature paper (King et al, 2012), used GRACE gravity data to infer the ice mass trends as in previous work, but with an updated estimate of the GIA correction.
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References

  1. M.A. King, R.J. Bingham, P. Moore, P.L. Whitehouse, M.J. Bentley, and G.A. Milne, "Lower satellite-gravimetry estimates of Antarctic sea-level contribution", Nature, vol. 491, pp. 586-589, 2012. http://dx.doi.org/10.1038/nature11621

Trying to shoot the messenger

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Does this sound familiar? A quantitative prediction is inconvenient for some heavily invested folks. Legitimate questions about methodology morph quickly into accusations that the researchers have put their thumb on the scale and that they are simply making their awkward predictions to feather their own nest. Others loudly proclaim that the methodology could never work and imply that anyone who knows anything knows that -it’s simply common sense! Audit sites spring up to re-process the raw data and produce predictions more to the liking of their audience. People who have actually championed the methods being used, and so really should know better, indulge in some obvious wish-casting (i.e. forecasting what you would like to be true, despite the absence of any evidence to support it).

Contrarian attacks on climate science, right?
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Short term trends: Another proxy fight

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One might assume that people would be happy that the latest version of the Hadley Centre and CRU combined temperature index is now being updated on a monthly basis. The improvements over the previous version in terms of coverage and error estimates is substantial. One might think that these advances – albeit incremental – would at least get mentioned in a story that used the new data set. Of course, one would not be taking into account the monumental capacity for some journalists and the outlets they work for to make up stories whenever it suits them. But all of the kerfuffle over the Mail story and the endless discussions over short and long term temperature trends hides what people are actually arguing about – what is likely to happen in the future, rather than what has happened in the past.

The fundamental point I will try and make here is that, given a noisy temperature record, many different statements can be true at the same time, but very few of them are informative about future trends. Thus vehemence of arguments about the past trends is in large part an unacknowledged proxy argument about the future.

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A sea level Golden Horseshoe nominee*

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I was reading a sign high on the wall behind the bar:

‘Only genuine pre-war British and American whiskeys served here’

I was trying to count how many lies could be found in those nine words, and had reached four, with promise of more …”

Dashiell Hammett, “The Golden Horseshoe”

Google News occasionally throws up some obscure postings that I would never otherwise come across. A recent example was a letter to an editor of a Scottish newspaper (not my usual reading material) declaring that “Climate change is not man-made”. The letter itself is uninteresting – a basic confusion between weather and climate seguing into a NIMBY-ish rant about windmills. Ho hum.

However, in one of the comments from a “Dr John Cameron, St Andrews” (posted 9/Oct/2012), there was this unrelated pseudo-factoid:

As regards the catastrophic sea level rise in the Pacific, it became obvious some 20 years ago that results from island tide gauges did not support computer predictions. Scientists from Flinders University in Adelaide set up new, modern, tide-gauges in 12 Pacific islands to test whether there was in fact any evidence of sinking. Recently the whole project was abandoned as there had been no sign whatsoever of a change in sea level at any of the 12 islands for the past 16 years.

Now this is specific enough to probably actually refer to something real, but doesn’t pass the sniff test for something that might actually be true. Scientists don’t set up monitoring stations only to get the answer they want and then stop monitoring if it doesn’t happen. This only happens in the fevered imaginations of conspiracy theorists. So I was intrigued enough to investigate what this actually referred to…
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Climate Change videos: Part I

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The US National Research Council has been doing a lot recently to expand background knowledge of the climate system and of climate change. In tandem with a new report discussing strategies for advancing climate modeling, they have put up a an introductory web site on climate models (including some interviews with some actual climate modelers).

More comprehensively, they have helped put together a series of videos discussing everything from the definition of climate to attribution of climate changes and future projections. The series is in seven parts, viewable here. There are additional resources here.

We thought it would be interesting to have a separate post on each of the seven videos so that discussions on the videos themselves, or the topics covered (or not) could be more focused. So, with no further ado, here is part I: “What is Climate?”

Embargos and confidentiality

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This post is not about climate science, but rather about the science/media interface.

As many of you may be aware, papers that are scheduled to appear in high-profile journals (Science, Nature and a few others) are often released a few days early to journalists under embargo in order to give them a chance to do a fuller story and talk to more people about it prior to filing. On balance, this works reasonably well, and the press stories that come out are on the whole better for it (there is a bigger issue with the need for a news peg for most science stories that this practice dominates, but that isn’t the focus of this post).

But Carl Zimmer and Maggie Koerth-Baker recently reported on a situation where a high profile paper was only provided to journalists under embargo if they signed a non-disclosure agreement restricting their ability to show it to other scientists for comment.

This is both very unusual and, frankly, appalling. Science and science publishing are not a branch of the PR industry but part of an open and self-critical process of inquiry. Authors and scientists who do not want their results discussed and/or criticised should not submit them for publication in the first place. As Koerth-Baker and Zimmer make clear, articles about new papers that are simply reworded official statements are not journalism at all. Indeed, the need for journalists to get an unaffiliated opinion from the author’s peers is an essential check on the occasional tendency of press releases to go over the top when pushing a particular study, and is something that should be happening more, not less.

This post is really just about putting on record that this is not a practice that ‘scientists’ are advocating for and we, like the journalists linked above, would strongly advise that if such conditions are imposed, journalists, journals and editors do not accede to them. That will help resolve the issue of whether ‘no publicity’ is indeed preferable.

Finally, while I am sort of on the topic of science journalism, can’t we please, please, please mandate the citation of the DOI tag in any online story about a new paper? Tracking down the actual paper being described is all-too-often far more difficult than it needs to be. (For example, the doi for the study referred to above took four links and a targeted google search to find. Why?).

Science journalism is going through a tough time at the moment, and practices that take the reporting of science further away from science as a process and more towards the repetition of ‘gee whiz’ factoids, should be resisted by anyone who cares about the public’s engagement with science.

References

  1. G. Séralini, E. Clair, R. Mesnage, S. Gress, N. Defarge, M. Malatesta, D. Hennequin, and J.S. de Vendômois, "RETRACTED: Long term toxicity of a Roundup herbicide and a Roundup-tolerant genetically modified maize", Food and Chemical Toxicology, vol. 50, pp. 4221-4231, 2012. http://dx.doi.org/10.1016/j.fct.2012.08.005

Why bother trying to attribute extreme events?

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Nature has an interesting editorial this week on the state of the science for attributing extreme events. This was prompted by a workshop in Oxford last week where, presumably, strategies, observations and results were discussed by a collection of scientists interested in the topic (including Myles Allen, Peter Stott and other familiar names). Rather less usual was a discussion, referred to in the Nature piece, on whether the whole endeavour was scientifically worthwhile, and even if it was, whether it was of any use to anyone. The proponents of the ‘unscientific and pointless’ school of thought were not named and so one can’t immediately engage with them directly, but nonetheless the question is worthy of a discussion.

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