New studies deepen concerns about a climate-change ‘wild card’

A recently published Washington Post article entitled “New studies deepen concerns about a climate-change ‘wild card’” references two published studies. In the Washington Post article the author reports that future climate change will lead to disruptions in global ocean currents. Specifically, the weakening of the Atlantic Meridional Overturning Circulation (AMOC) system is discussed. This circulation system is responsible for transporting warm water northward, and cold, dense saltwater down into the deep ocean. The water circulation pathway helps to keep temperatures moderate in Europe.

One of the referenced studies, entitled “Response of Atlantic overturning to future warming in a coupled atmosphere-ocean-ice sheet model”, uses computer modeling to study the effects of rapid thawing of Greenland’s ice sheets. The study is published in Geophysical Research Letters and explores the AMOC’s sensitivity to changes in ocean temperature and freshwater perturbations. Previous studies have been conducted to explore Greenland ice sheet (GIS) melting, however, this study incorporates a new modeling technique that more accurately predicts the effects of freshwater incorporation into the AMOC system. The new modeling technique predicts more dramatic changes than previously expected from previous modeling techniques. The dynamic ice sheet model predicts weakening of the AMOC, and describes the intensification of the high-latitude halocline as a result of the freshwater discharge into the North Atlantic by GIS melting. Furthermore, the salinity decrease of the upper layer water inhibits North Atlantic Deep Water (NADW) due to the fact that freshwater is less dense than fresh water.

Figure 2 shows changes in salinity in the North Atlantic as a result of the GIS melting modeling. The dynamic modeling predicts a decrease in practical salinity by 2 units, while previous modeling systems predicts a decrease in practical salinity by 1 unit. This figure highlights what previous modeling systems failed to take into account.

   

The other referenced study, entitled “gradual onset and recovery of the Younger Dryas abrupt climate event in the tropics”, discusses the Younger Dryas (YD), a rapid climate change event that occurred 12.5 thousand years ago, also known as the Big Freeze. In this study published in Nature Communications, they use modeling to study this major past geological event to make predictions on future climate events. The current hypothesis for the cause of the YD is that a rapid freshwater influx into the North Atlantic weakened the AMOC and induced the abrupt climate change. In the paper, modeling using new hydroclimate records from the tropics is combined with previous established hydroclimate data to make future climate event predictions. Overall, much of the data reported in this study is analysis of the past. I think this paper was referenced to show an extreme example of global climate change (the YD), and the potential extreme implications of a weakening AMOC.

In short, both studies use modeling to predict weakening of the AMOC as a result of global climate change, which leads to predictions for future weather patterns and climate. They both use newer modeling systems to add to previously established research. I think overall the popular media article overhyped the reported research by using phrases such as “dramatic implications” and making references to movies such as “Day After Tomorrow”. Furthermore, I think when they claim that “possible effects [range] from plunging temperatures in the northern latitudes to centuries-long droughts in Southeast Asia” is a severe over-exaggeration of the reported research. The article also claims that global climate change may lead to the “shut down” of the AMOC, while the scientific articles report a weakening of the AMOC. However, when the scientific papers are described in the Washington Post article, I think the research was well summarized (though very briefly) and it is clearly mentioned that computer modeling was involved. Quotes from the authors of the peer-reviewed papers were included in the Washington Post article, which allowed for a more dramatic spin on the reported research. 

Popular media article:

http://www.washingtonpost.com/news/energy-environment/wp/2015/09/07/new-studies-deepen-concerns-about-a-climate-change-wild-card/

Peer-Reviewed articles:

http://onlinelibrary.wiley.com/doi/10.1002/2015GL065276/full

http://www.nature.com/ncomms/2015/150902/ncomms9061/full/ncomms9061.html