Structured Expert Elicitation: Can Polling Predict Future Sea Level Rises?
    By News Staff | January 6th 2013 04:45 PM | 6 comments | Print | E-mail | Track Comments

    It's statistical polling...for science. 

    A paper in Nature Climate Change uses structured expert elicitation and mathematically pools experts' opinions to forecast future sea level rises from melting ice sheets. Soliciting and pooling expert judgments is used in eruption forecasting and the spread of vector borne diseases - with questionable accuracy - and in their paper Professor Jonathan Bamber and Professor Willy Aspinall from the University of Bristol try to model the uncertainties in the future response of the ice sheets. 

    The ice sheets covering Antarctica and Greenland contain about 99.5 percent of the Earth's glacier ice, they would raise global sea level by over 60 meters if they were to melt completely (it's not happening, relax) and so any melting of ice sheets is considered the largest potential source of future sea level rise. That is where there is also the largest uncertainty so predicting their future response using numerical modeling is part science and part magic.

    Structured expert elicitation found that the median estimate for the sea level contribution from the ice sheets by 2100 was 29 cm with a 5 percent probability that it could exceed 84 cm. When combined with other sources of sea level rise, the authors state a conceivable risk of a rise of greater than one meter by 2100. The IPCC's last report estimated 18-59 cm for six possible scenarios so 100 cm is obviously aggressive, but that is why they use the term 'conceivable'.

    Scientists, as a group, are highly uncertain about the cause of the recent increase in ice sheet mass loss observed by satellites, the modelers note, and equally unsure whether this is part of a long term trend or due to short-term fluctuations in the climate system. 

    Bamber said: "This is the first study of its kind on ice sheet melting to use a formalized mathematical pooling of experts' opinions. It demonstrates the value and potential of this approach for a wide range of similar problems in climate change research, where past data and current numerical modelling have significant limitations when it comes to forecasting future trends and patterns."


    Polling? This is not science. It's politics. Don't confuse the two.

    The part that is not clear is whether the one meter rise is estimated with or without reductions in CO2 emissions. That seems to me to be an important distinction.

    I would like to see a more detailed report, something like this: A one meter rise is a 5% probability if we reduce emissions, or greater that 50% probability if we don't.

    Without that clarification all we can do is guess, which is an unfortunate situation on such an important issue.

    It would also be nice to know an estimate of the rate of sea level rise by 2100. If sea level rises one meter I don't think it is going to magically stop at the year 2100. I have seen some estimates that it may be rising at that point at a rate of 30cm per decade, which would make it nearly impossible to build sea walls or even ship docks and piers that can keep up with the changing level.

    Isn't the IPCC 2007 report based on science re 2005 and leaves out of its assessment land-based ice and feedbacks? Won't next IPCC report yet leave out Arctic carbon feedbacks (again) while only including a ~1.0 version re feedbacks? Hasn't the science limited itself to the 21st century impacts of the Anthropocene to keep the work of integrating specialized scientific knowledge focused due to an inability to know how to model integration and feedbacks over longer time frames limits the scope of what can be determined about them--ie not that tipping points re land-based ice don't exist, but we don't know how to model how anthropogenic greenhouse gases will interplay with the dynamic balance that defined the Holocene and land-based ice sheet behavior?

    Consider the unfolding loss of sea ice in the Arctic re the IPCC's 2007 assessment and revisit the assertions made in this report about what to "relax" about. Then do some research on motivated reasoning, and some self-reassessment. In matters of physics there is no 'early' re the current observed collapse of the Arctic's summer ice cap and the IPCC's 2007 report. To what degree is implying that one can be scientific and rational and relax, re threats of land-based ice sheet collapse, little more than human hubris–and a pandering to it?

    I think this is fantastic. As a researcher, I work in both the hard and soft sciences. Each of them have their strengths and weaknesses. Hard sciences tend to be more accurate, replicable, and defendable. However, because they are empirically driven, results corresponding to complex phenomenon are difficult to generalize. Soft sciences, on the other hand, tend to take a more top-down approach and are thus more holistic. The incorporation of expert opinion is especially helpful in interjecting the "big picture" into predictive modeling of complex behavior. Solutions to modern problems require a transdisciplinary approach.

    I'm an engineer. It seems this article is promoting that on the next bridge that I build, I should poll my friends and ask them how big the beams should be. Not a good plan.

    Isn't that what the ASME book is, anyway?  It isn't like you calculate everything all over again.

    But, sure, your point is valid. It seems kind of strange to take polls of experts and then average them, get an answer 40% higher than the supposed experts of the experts and declare the IPCC must be wrong.