Failed Predictions of Climate Science, Part 1: Wadhams on Summer Sea Ice
A little over a decade ago, a scientists by the name of Peter Wadhams made a bit of a splash in by doing a few interviews in which he predicted that the Arctic would begin experiencing summers free of sea ice ice by around 2018. Perhaps the most popular story featuring his claims was published the Guardian in 2016 (similar article was published in the Guardian in 2012), and since it was an interview, it seems highly likely that Wadhams was given the ability to offer qualifications or nuance to his claims. I think the most relevant excerpt from the interview is:
The overall trend is a very strong downward one, however. Most people expect this year will see a record low in the Arctic’s summer sea-ice cover. Next year or the year after that, I think it will be free of ice in summer and by that I mean the central Arctic will be ice-free. You will be able to cross over the north pole by ship. There will still be about a million square kilometres of ice in the Arctic in summer but it will be packed into various nooks and crannies along the Northwest Passage and along bits of the Canadian coastline. Ice-free means the central basin of the Arctic will be ice-free and I think that that is going to happen in summer 2017 or 2018.
It's now 7 years after 2018, and clearly this didn't happen. We could blame this on Wadhams giving a bit of an sensationalistic interview, perhaps, but a paper he published in 2012[1] offered a similar, though more nuanced and careful conclusion. In the quote below, FY is first year and MY is multi-year ice.
The sea ice cover in the Arctic Ocean is undergoing a transition from being a perennial (year-round) ice cover to a seasonal cover resembling the Antarctic, where most of the ice is FY and disappears in summer. The trend towards smaller areas in summer, which reached a temporary peak in 2007, will resume, and will lead to an ice-free summer Arctic in less than 30 years. The ice cover in the winter Arctic will be primarily FY, so that it will be passable by polar icebreakers at any season, with a milder pressure ridging regime which has implications for the design of offshore structures such as drilling platforms. The open water in summer will not only allow unrestricted shipping, but will result in a warmer ocean regime leading to loss of methane from melting permafrost, itself accelerating global warming, as well as increased precipitation over the land masses surrounding the Arctic Ocean and an increased melt rate for terrestrial ice sheets such as that of Greenland. Within a decade we can expect summer ice to be largely confined to a redoubt north of the north coasts of Greenland and Ellesmere Island, the only location where substantial MY ice will be found.
Here Wadhams claims that the first Arctic summer free of sea ice would occur before 2042, but by 2022, summer sea ice would be "largely confined to a redoubt north of the north coasts of Greenland and Ellesmere Island," since multi-year ice would only be found in those areas. This did not happen either. Sea ice volume continues to decrease but MY ice is not confined to those areas. But this plot of models vs observations from his 2012 paper[1] might show why he thought this.
 |
| Wadhams 2012 |
Clearly the observed trends gave the appearance of the Arctic losing September sea ice much more rapidly than model predictions. The star on the graph above is for 2007. September 2012 was even lower, and this appears to be the kind of data that fueled Wadhams' rather "alarmist" predictions. This represents his predictions compared to the IPCC's projections from AR5 models using RCP8.5.
So Wadhams' prediction was an outlier prediction, and it did not go unnoticed by his fellow climate scientists, who did provide criticism of Wadhams' claims. A Science Feedback article on the Guardian interview gave it a "low" score for scientific credibility based on the reviews of several scientists. Ed Hawkins summarized what appears to be the general view of the scientists reviewing the interview.
Peter Wadhams’ views are well known to lie far outside the scientific mainstream. He makes several statements that are inaccurate and some are alarmist. There is no balance in the article from a more mainstream scientist.
The scientists reviewing Wadhams' claims reiterate that the scientific mainstream accepts the model predictions that the first Arctic summer free of sea ice is likely to happen around the middle of the 21st century, with a possibility that it could occur earlier given a high emission scenario (RCP 8.5). Alexis Berg writes,
Readers should be reminded that under a business-as-usual greenhouse gas emissions scenario, climate models project an “ice-free” (less than 1 million km^2 of ice) Arctic in September by ~2050. Peter Wadhams claims almost every year that it will happen sooner than that, in a matter of a few years – implying some total collapse of Arctic sea ice.
A linear extrapolation of short-term data would give the impression of a rapid collapse of sea ice by 2018, but a linear extrapolation from short-term data is rarely a good predictive strategy, especially when not grounded in sound physics. And there was good reason to think that this could be a short-term departure from the long-term decline trend. In fact, a couple years earlier on Twitter (now X), Gavin Schmidt was even more severe in his criticism of Wadhams' views.
So Wadhams' prediction was an outlier prediction significantly outside both model predictions and what mainstream scientists were saying at the time. This prediction does not provide evidence that mainstream climate science does not have a handle on how rapidly the Arctic is losing sea ice. It is I think a reminder that we should never take outlier studies and imagine that these automatically supplant the conclusions of the majority of papers. The gold standard for science is not novelty but replication.
References:
[2] Wadhams, P., N. Hughes, and J. Rodrigues (2011), Arctic sea ice thickness characteristics in winter 2004 and 2007 from submarine sonar transects, J. Geophys. Res., 116, C00E02, doi:10.1029/2011JC006982.
[3] Wadhams, Peter; A Davis, Norman R. (2000) Further evidence of ice thinning in the Arctic Ocean. J Geophysical Research Letter, vol 27 no 24 pp 3973-3975 0094-8276. https://doi.org/10.1029/2000GL011802
https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2000GL011802
Comments
Post a Comment