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Physicist Retired
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From NewScientist: "Arctic ice grows darker and less reflective" "For the first time, a detailed analysis of 30 years of satellite data for the Arctic Ocean has quantified how much the albedo, or reflectivity, of Arctic ice is diminishing. Aku Riihela of the Finnish Meteorological Institute told New Scientist he estimates that darker ice means the Arctic Ocean's albedo at the end of the summer is of the order of 15 per cent weaker today than it was 30 years ago. ...The authors of the new paper have not yet calculated the effect of their findings on those predictions. But they can only hasten the day when the Arctic is ice-free in summer."
Regarding "Arctic sea ice response to atmospheric forcings with varying levels of anthropogenic warming and climate variability" I think it's important to understand that this study used data ending in 2009, and projected forward from there. In 2009, the researchers had one 'outlier' to work with (2007) - and treated it as such. You can access the entire paper here: Notice Figure 1, page 2 (especially (e - volume), but also (d - extent)). The 'expected recovery' of ice in 2010 is quite noticeable in those graphs. Results from then on will be highly skewed towards longer timeframes for an ice-free Arctic. Of course, just 4 years later, we have far more 'interesting' data. One wonders what Zhang et al would look like if it were recalculated today.
Are scientists conservative about Arctic sea ice? Yes. Scientists are also conservative about estimating the speed of plant/animal migration away from the poles, the rate of climate-change-induced extinctions, permafrost melting, and a whole host of other phenomena. jmp (above) identifies one part of the problem here - the rate of climate change is incredibly fast. The Scientific Method and peer review, on the other hand, impose a more conservative bias. Climate predictions, like the rate of Arctic sea ice loss, are based on models. But models are imperfect, and many of the mechanisms driving rapid loss of sea ice are too poorly understood to incorporate into those models at all. How rapidly will the upper layer of the Arctic Ocean warm - and by how much? At what rate will Arctic air temperatures rise (thus increasingly changing precipitation from insulating snow to ice-melting rain)? How will reduced sea ice alter atmospheric patterns and systems in the Arctic Circle (a question Neven has raised several times now)? Etc. We may know these things are happening, but we have far too little data to accurately model them. Scientists know that 'an abrupt and persistent change in [Arctic] sea-ice dynamics' occurred in 2007. They just don't know (precisely) why. Models don't show it. Models, instead, show many paths to 'stable' states (and even recovery), but not 'rapid and persistent' change. The good news here is that some (new) research recognizes the fact that models and observational data are incompatible - and that observational data should be included in sea ice predictions even when the models say something completely different. Here, for example, is the Abstract from Overland and Wang (2013). I apologize in advance for the long quotation, but I think it's an important one: "The observed rapid loss of thick multiyear sea ice over the last 7 years and the September 2012 Arctic sea ice extent reduction of 49% relative to the 1979–2000 climatology are inconsistent with projections of a nearly sea ice-free summer Arctic from model estimates of 2070 and beyond made just a few years ago. Three recent approaches to predictions in the scientific literature are as follows: (1) extrapolation of sea ice volume data, (2) assuming several more rapid loss events such as 2007 and 2012, and (3) climate model projections. Time horizons for a nearly sea ice-free summer for these three approaches are roughly 2020 or earlier, 2030 ± 10 years, and 2040 or later. Loss estimates from models are based on a subset of the most rapid ensemble members. It is not possible to clearly choose one approach over another as this depends on the relative weights given to data versus models. Observations and citations support the conclusion that most global climate model results in the CMIP5 archive are too conservative in their sea ice projections. Recent data and expert opinion should be considered in addition to model results to advance the very likely timing for future sea ice loss to the first half of the 21st century, with a possibility of major loss within a decade or two." That, to me, is an astounding statement. I can think of very few times in the history of science when rapid change (with very serious consequences) outpaced our understanding - and scientists were therefore forced to give weight to data that they couldn't explain. In the case of the Arctic, then, we may very well find ourselves in the position of watching science remain continually behind the curve - because the rate of change far outpaces our ability to understand how all the moving parts combine to create the phenomena we're actually seeing. At least, that's what I expect to see in the near term.
Physicist Retired is now following The Typepad Team
Jul 30, 2013