Summary of Article:
The article details a "growing body of evidence" that suggests that the Atlantic meridional overturning circulation (AMOC) is weakening, which has "implications for everything from the climate of Europe to the rates of sea-level rise along the U.S. East Coast." As the actual flow has only been measured since 2004 (the period is too short to establish a trend), a new study published in Nature Geoscience cites "proxy" research, drawing conclusions about the circulation's strength from ocean temperature patterns and clues in seafloor mud. From these, the scientists have determined that the AMOC is at its weakest point within the last 1000 years, has weakened by about 15% since around 1950. The AMOC is conducted by a system involving both temperature and salt, known as the thermohaline circulation. This is the Earth's "conveyor belt", circulating heat from the Northern and Southern hemispheres (cold water circling to the South, and warm water circling to the North). Because of melting glaciers in the North as a result of climate change, the northern water is becoming fresher and less salty (therefore less dense). According to Wallace S. Broecker, the AMOC is the 'Achilles' heel' of the climate system, with the potential to cause intense cold periods in the Northern Hemisphere, and odd temperature patterns already present that are "significantly upending ... coastal fishes". Additionally, a persistent "cold blob" has been spotted in the Northern Hemisphere, indicating the current circulation slowdown. Finally, the article comments on the study's reliance on only proxy studies and suggests that while the conclusions may be challenging to draw because the proxy measurements may not accurately reflect the ocean circulation, it can still provide a big picture (a "3-D AMOC circulation") that can give us a better understanding of the AMOC system.
Science in the Article:
Overall, the article heavily backed up the science behind their analysis of the study by linking several other studies and providing expert commentary. Based on this, I feel that the news article did not shy away from incorporating information from as many scientific articles as possible in an effort to give an accurate representation of the issue and showcase that this new study is backed up by plenty of evidence. The main study that is being reported on by the Washington Post is titled, "Current Atlantic Meridional Overturning Circulation weakest in last millennium" by Caesar et al, published online on 25 Feb 2021. The study indicates that its analysis is based on comparing "a variety of published proxy records to reconstruct the evolution of the AMOC since about AD 400." They found that, following a long stable period, starting in about the nineteenth century, there was an initial weakening that, in the mid-twentieth century, became a more rapid decline." Based on the results reported in the study, I think the Washington Post summarized these results accurately in their article. They also state that the AMOC is at the weakest it has been in the last "millennium or more"; the study dates back to AD 400, which as of now is about 2021-400 = 1021 years ago. So this restating of the timeline in the news article is accurate.
Another scientific article published in April 2018 linked in the news article is titled "Anomalously weak Labrador Sea convection and Atlantic overturning during the past 150 years" by Thornally et al. Here, the scientists report on the significant weakening of the AMOC over the past 150 years, as compared to the last 1500 years. This timeline is different from the one in the report in that it goes back farther than one millennium; yet, the conclusions made are in line with the newest study. The scientists suggest that "enhanced freshwater fluxes from the Arctic and Nordic seas... sourced from melting glaciers and thickened sea ice ... weakened Labrador Sea convection and the AMOC." This is in sync with the Washington Post's explanation for rising fresh northern water as compared to salty water due to the greater melting of glaciers. The study also goes on to propose that future studies should focus on "climate variability" and "anthropogenic forcing" (human influences) on the AMOC weakening.
Finally, the news article links a third scientific article also published in April 2018 titled, "Observed fingerprint of a weakening Atlantic Ocean overturning circulation" by Caesar et al (the same first author as for the main recent study). This article reiterates the "lack of direct current measurements" of the AMOC that was also mentioned in the news article, indicating the need to rely on proxy evidence to provide evidence for the AMOC weakening. Here, the scientists reported that the AMOC has weakened by about 15 percent since the mid-twentieth century, as indicated in the news article. The scientists identified a blue "fingerprint" in the northern Atlantic Ocean, (accurately) referred to in the news article as the "cold blob." This marker has been persistent over the latest few years and can be explained, according to the scientists, by "reduced northward heat transport" due to weakening circulation, which is the same reason given by the Washington Post. This scientific article also references the AMOC as a "tipping element" of the climate system, which suggests that its potential as the "Achilles' heel" of our climate as proposed in the news article.
Assessment: Was Science Misused?
Based on my analysis of three related scientific articles (which also were cited in the news article itself), I believe that this news article did a very good job of representing the science accurately. Beyond the scientific articles I analyzed, the news article also referenced additional scientific articles to discuss additional concepts, such as the trends we are seeing currently in the "upending of certain key fisheries" as a result of the AMOC weakening. Overall, I would say that this article represented the issue very well and gave enough weight to the most important takeaways, along with drawing a fair amount of concern to the slowing Atlantic Ocean circulation and the drastic consequences it can have. I can imagine that this could be a difficult concept for the general public to understand, but the Washington Post explained the science behind the Atlantic Ocean circulation very clearly and simply for most people to comprehend. The one comment I had was on one statement they made: "Scientists do not expect anything so severe in our future, especially because greenhouse gases will continue to cause offsetting warming." While intuitively this makes sense, I would have liked to see this news article back this claim up by the science and question how much global warming offsets cold periods in the Northern Hemisphere caused by the AMOC weakening. Overall, I believe that this news article did not misuse science and represented this issue very accurately.
Thanks for reading!
Hi Anusha,
ReplyDeleteThis was a very interesting topic as I have never known about the Atlantic Meridional Overturning Circulation (AMOC) and its link to climate change as the “Achilles heel.” I would like to know more about why and how the AMOC is weakening as it is correlated to sea-levels rising. It was also very interesting to learn that a more rapid decline since the mid-twentieth century of the AMOC has been reported which makes me think about major population increases during that same time (along with increased emissions). Future studies on how humans influence the AMOC would be eye-opening as we already know so much about man-made emissions causing climate change in other ways.