Comprehensive study of West Antarctic Ice Sheet finds collapse may be unavoidable

 News Article: https://www.nbcnews.com/science/environment/west-antarctic-ice-sheet-collapse-may-unavoidable-study-finds-rcna120993

Scientific Paper: https://www.nature.com/articles/s41558-023-01818-x

"Comprehensive study of West Antarctic Ice Sheet finds collapse may be unavoidable" is an article written by Evan Bush, published by NBC news on  October 23rd, 2023- the same date as its corresponding scientific paper. The Nature Climate Change published article, titled "Unavoidable future increase in West Antarctic ice-shelf melting over the twenty-first century", is authored by Kaitlin Naughten and Paul Holland of the British Antarctic Survey, as well as Jan De Ryt of Northumbria University. The paper discusses the floating ice shelves in the Amundsen Sea, a body of water off the coast of West Antarctica. Naughten et. al make the claim that the ocean-driven melting of the Amundsen Sea ice shelves, which is the main process in Antarctica's contribution to sea-level rise, is not subject to significant mitigation by greenhouse gas reduction. Through the analysis of five scenarios of varying severities, the researchers approached the following questions: How much of the West Antarctic Ice Sheet melting is unavoidable? How much of the melting can be mitigated by the reduction of greenhouse gas emissions? And how long do we have left before these scenarios become a reality? 

My initial impression of Bush's NBC News article was generally a positive one, with a couple of caveats. I believe the article encompasses the implications of the scientific article well- by interviewing outside researchers as well as the main authors of the paper, Bush takes the same angle that the scientific paper does: that there's a lot of uncertainty around this phenomena. The effects of the West Antarctic Ice Sheet (WAIS) melting are severe, however there is lack of historical data, and factors such as ice-sheet geometry as melting occurs or snowfall levels over the centuries have not been considered in this study. The study is the first of its kind, a comprehensive ensemble of ocean-condition data that emphasizes how past and present conditions will inform the future centuries, modeled in differing climate scenarios from least to most optimistic. I appreciated that Bush's article emphasized the human impact of WAIS melting. This is an approach that is familiar to news outlets publishing about climate change, however I think that Bush does it a bit better than I've seen previously. A quote that the article emphasized comes from Kaitlin Naughten herself, where she states that, as a result of eventual West Antarctic ice shelf melting, Coastal communities will either have to build around or be abandoned.” This is an important piece of information, especially coming from the first author of the paper, however I don't think it necessarily captures the main takeaway of the scientific paper. 

The scientific article uses historical data, which has been gathered in the Amundsen Sea only since 1994, as well as current climate conditions, to inform their claims. The study not only analyzes the worst case melting scenario for fossil fuel use, it also analyzes the best case scenario as well as considering two middle-ground scenarios. A regional ocean model of the Amundsen Sea, known as the MIT general circulation model as the ice-ocean model for this study, which takes into account atmospheric forcing of ice-sheet conditions. This model does simulate the ice-shelf basal melting as well as variations in the freshwater surrounding the region, but it does not take the changing ice shelf geometry into account. 

The five scenarios modeled in the study are a historical scenario (1920-2005), Paris 1.5°C and Paris 2°C, which follow the goals of the Paris Agreement, RCP 4.5 and RCP 8.5, which follow Representative Concentration Pathways for future anthropogenic forcing, assuming medium fossil fuel use for RCP 4.5, and high fossil fuel use for RCP 8.5. All scenarios that were considered take the warming of the Amundsen Sea as inevitable. 

Figure 1, shown above, displays a spatial distribution of trends for the Paris 2 °C scenario. Mid-depth temperature, which includes the water that directly affects the cavities in the affected ice shelf, are taken and analyzed at a 200-700m mean. The color map is not the most clear to read in my opinion, but the data displays that there is significant correlation between mid-depth temperature and ice-shelf basal mass loss. The white regions contain no significant temperature trends. 

The data also found that, even under the most ambitious mitigation scenario, which is Paris 1.5°C, the Amundsen sea is predicted to warm three times faster than in the 20th century. This is due to the projection of future warming and melting trends increasing from the historical 0.25°C per century to a much greater 0.8-1.4°C per century. 

When the ocean temperatures were analyzed over time in the five core scenarios, all were found to have similar mean values for much of the century. RCP 8.5, the worse-case climate change scenario, diverges from the other ensembles in 2045. 

Even if the worst case-climate scenario was mitigated, the melting trends would still continue for several decades before an effect is observed. By this time, even if ocean temperatures returned to present day values, which is also unlikely, the impact on glacial basins in the WAIS could be irreversible. The ice shelf is made up of many components: a seasonal surface layer, a subsurface year-round cold winter water layer, and below that, a warm circumpolar deep water. These layers are separated by the thermocline, which is a sharp temperature gradient around 100-400m below the surface. Overall, the claim made is that the warming of the continental shelf is driven by an increase in the circumpolar deep water (CDW) volume on shore. The authors also state that the simulations all show increases in the Amundsen undercurrent, a current that transports the CDW eastward, which would lead to warming of the continental shelf. 

Overall, the simulations performed in the study show that substantial ocean warming and ice shelf melting are present in all future climate scenarios, even the ones that are considered unrealistically optimistic. The mid-range scenarios, such as RCP 4.5, Paris 1.5, and Paris 2.5 are deemed to be statistically indistinguishable in terms of warming trends. It was found that the Amundsen Sea conditions in the year 2100 could be up to 2°C warmer than pre-industrial conditions. They found it important to note that their study does not discount anthropogenic mitigation altogether in order to limit the impacts of climate change. It finds, however, that adaptation must be considered more seriously as a response to rising sea levels. 

I think that the NBC article avoids a lot of the details that are important in the paper, and brings in multiple sources from the outside to pad the article. It focuses on communities that could potentially be impacted by the projected sea-level rise, while also emphasizing the overall uncertainty of the future projections, simulations, and attitudes towards the severity of WAIS melting. It is not often that we see a scientific article conclude with a recommendation to rely on mitigation, adaptation, and luck, in order to limit the effects of sea-level rise. I would rate the the NBC article a 7.5/10, as I feel like it captures the sentiment of the research authors well, but it does not really provide any specific data from this paper to back up the claims. The five core scenarios that were considered in the scientific paper were not explained in the NBC article, only a couple sentences were used to talk about a worst-case and best-case scenario, and that "nothing made a substantive difference over the next several decades." The NBC article does, however, do a good job of emphasizing that this study is only a first step in the direction of future modeling projections, and that there are many gaps in this study that must be filled in the future to provide a more accurate model.