My project ice2sea is currently in the news. For example, the BBC: ‘Best estimate’ for impact of melting ice on sea level rise.
Ice2sea is an enormous project, involving 24 institutions (such as universities and meteorological institutes), which were mostly in the EU but also further afield. Our aim was to improve observations and modelling of continental ice – the Greenland and Antarctic ice sheets, and the world’s glaciers and ice caps – to improve understanding about their behaviour in the recent past and projections of how they might change in the future. The main aim was to support the Intergovernmental Panel on Climate Change (IPCC) in assessing current understanding of sea level change. Ice2sea is an umbrella over many areas of research, which makes it difficult to summarise the results in a few quotes.
The reason we are in the news now is because we are having our final project meeting at the Royal Institution (Ri) in London this week. Many of the scientists involved in ice2sea, from across the EU and beyond, are gathering together to give talks on their work and discuss the results. Three of us are also giving a free public talk tomorrow at 7pm.
Publications and collaborations will continue long after the end of the project. We have a legacy of improved models, robust observations, and new scientists. I’m certainly planning to continue working with many of my ice2sea collaborators in the future.
Given that we are meeting at the Ri for three days, and the project is slowly drawing to a close, ice2sea held a press conference yesterday morning explaining what the project is, what our aims were, and what we feel we’ve achieved. Most of this focused on the benefits of this kind of project – the international collaboration, exploiting expertise from different countries, and the coordinated study of all aspects of continental ice.
We’ve produced a summary document, “From Ice To High Seas” that explains the science of continental ice and sea level to a general audience and highlights the individual publications that we’ve produced. It describes ice2sea papers that have been published in journals but also those that haven’t yet completed peer-review. So the document is a summary of our research as of April 2013, but the final results may change as these papers work their way through the system.
There are two sets of numbers from our summary document that have been highlighted by the media. I’ll explain where these come from:
“For that one scenario we have an ice sheet and glaciers contribution to sea level rise of between 3.5 and 36.8 cm by 2100,” – David Vaughan
“They concluded there was a one in 20 chance that the melting ice would drive up sea levels by more than 84 centimetres, essentially saying there’s a 95% chance it wouldn’t go above this figure.” – Matt McGrath
The first is a summary of the publications that make projections using models of the atmosphere, ocean, ice sheets and glaciers. The scenario David Vaughan (from the British Antarctic Survey, the ice2sea project leader) refers to is a “mid-range” emissions scenario, SRES A1B. Most, but not all, of these papers have completed peer-review. The list of papers relevant to that range is at the end of the post. We stated the minimum and maximum range of these projections in the summary document.
The second is from one publication (Bamber and Aspinall, 2013: listed below) that uses “expert elicitation”, a structured way of combining the judgement of a group of experts. This method deserves its own post, but here is an article about it by Willy Aspinall from the University of Bristol. This estimate is across all scenarios, not just one in particular.
So the first is the range of results from different plausible modelling options for the A1B scenario, while the second is an expert assessment of the probability of sea level rise given that the models do not incorporate every process and we may not follow the A1B emissions scenario.
Many of these papers will be included in the IPCC Fifth Assessment Report (AR5) being published this September; others will not, for example if they were not accepted by journals in time for the AR5 deadline. But this interim summary of our own work is not intended to “compete” with the IPCC, because that will assess all sea level research worldwide rather than only ice2sea results.
Not only that, but these papers are a small part of the results of ice2sea. We also have also led or contributed to major steps forwards in observing and modelling continental ice and sea level change, including:
- reconciled estimates of Greenland and Antarctic ice sheet mass changes (Shepherd et al.)
- the most detailed and complete inventory yet of the world’s glaciers (the Randolph Glacier Inventory)
- detailed maps of the bedrock under the Greenland and Antarctic ice sheets (Bamber et al., Le Brocq et al.)
- improved modelling of the climate over the Greenland and Antarctic ice sheets (e.g. Fettweis et al., Rae et al.)
- improved modelling of the ice sheets (e.g. Favier et al., Nick et al., Ligtenberg et al.)
We also have a special issue in The Cryosphere (open access).
Our focus has very much been on improving our understanding of the processes involved. This is a different approach to several recent studies that have used very simple assumptions or relationships to make projections for the future (such as extrapolation of past trends). Our work, such as our projections for Greenland glaciers (Nick et al.), shows that continental ice is complex, and can have both periods of rapid change and of relative stability. We can’t just extrapolate the past into the future. We need to understand the processes of ice, the detailed landscape of the bedrock underneath, and the potential range of changes to the atmosphere and oceans, to make physically-based projections of the future.
Update: some are asking about comparisons of our summary range with the previous IPCC projections (AR4).
First, the ice2sea headline results are the substantial improvements in models and observations, not our simple summary of the minimum and maximum projections.
Second, we should be cautious of comparing with AR4 land ice contributions for the same scenario (A1B), because those projections were from 1980-1999 to 2090-2099 while ours are for 2000-2100, and theirs are stated as a 5-95% range while ours don’t have a probability range attached.
Third, there’s another reason we can’t compare with the total sea level contributions: they combined the land ice and thermal expansion contributions using an assumption that they are independent, but we haven’t repeated this analysis.
There is a quote from David in the BBC article about our high end estimate being about 10cm higher than AR4, but this was a spur-of-the-moment, back-of-the-envelope comparison (in response to a press request) with the best-known AR4 range which includes all scenarios, just to provide some context. It’s not meant as a definitive, like-for-like comparison. Even if he had said about 17cm higher, the difference for the A1B land ice contributions, it would still have been a ballpark figure because of the different definitions of the contribution. That is why we haven’t made that comparison in the summary document.
In short, do wait for the AR5 in September for consensus sea level projections and how they compare with AR4. For ice2sea, please have a look at individual publications, and the summary document, but bear in mind that we are not trying to do the job of the IPCC: rather we have spent considerable effort trying to make their job easier, by providing science reported in individual publications.
Bamber and Aspinall (2013) “An expert judgement assessment of future sea level rise from the ice sheets”
Fürst et al., in review.
Goelzer et al. (2013), “Sensitivity of Greenland ice sheet projections to model formulations”
Payne et al., in review.
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