Studies Say Climate Change Weakens Key Atlantic Ocean Current

In recent years, it has been reported that the Atlantic meridional overturning circulation (AMOC), a major ocean current, is weakening. The United Nations Intergovernmental Panel on Climate Change Sixth Assessment Report (AR6), the sixth series of IPCC reports, suggests that the AMOC will likely weaken over the 21st century due to high GHG emissions. Still, its total collapse is unlikely to happen before 2100.

However, recent studies show that the latest IPPC report may have overestimated the stability of the AMOC because it didn’t accurately consider freshwater inputs from melting glaciers, ice sheets, and rivers due to increases in rainfall as the planet warms.

The Atlantic Meridional Overturning Circulation (AMOC) is an extensive ocean current system that carries heat and salt through the global ocean and strongly modulates regional and global climate warm water from the tropics northwards into the North Atlantic.

A new study published in Science Advance in February 2024 shows that the AMOC is on the verge of collapse because of freshwater input in the North Atlantic. According to the study, the collapse of this critical ocean current will result in freezing temperatures for Europe, scorching temperatures for the tropics, and an increase in sea level in the North Atlantic.

Another study published in Nature Communications on July 2023 warns of a forthcoming AMOC collapse due to increasing greenhouse gas concentrations. The study based its prediction on observations such as increasing variance (loss of resilience) and increased autocorrelation (critical slowing down) of the AMOC. Researchers estimate the collapse of the AMOC to occur as early as 2050 under the current scenario of future emissions.

The increase in freshwater flows to the Arctic Ocean is supported by the study published in the Environmental Research Letters journal in June 2023. The study shows that the unprecedented rate of Arctic warming in recent decades has accelerated the high-latitude landmass hydrological cycle, leading to increased river discharge into the Arctic Ocean and that long-term river discharge has been steadily growing, particularly in 2020, with the total annual discharges of the eight largest Arctic rivers at 2623 km3 12% greater than the 1981–2010 discharge average.

The National Snow and Ice Data Center also shows that as of 2021, the Greenland and Antarctic Ice Sheets collectively contribute about 400 billion tons of water from icebergs or meltwater runoff, adding about 1 millimetre to sea level each year. According to the Centre, for every centimetre (10 millimetres) in global sea level rise, another 6 million people are exposed to coastal flooding.

The slowing down of the AMOC is observed in the North Atlantic and the Southern Hemisphere for the same reasons. A study published in Nature in March 2023 shows that the melting of the Antarctic is slowing the abyssal ocean circulation. The authors find that meltwater input around Antarctica drives a contraction of Antarctic Bottom Water (AABW), opening a pathway that allows warm Circumpolar Deep Water greater access to the continental shelf. The study findings highlight the critical importance of Antarctica meltwater in setting the abyssal ocean overturning, which has implications for the climate that could last for centuries.

The studies using various data and methods point to a single outcome: the likelihood of an AMOC collapse in the near future or within the next decade could disrupt climate globally. For instance, it can shift the Asian monsoon rainfall patterns and reverse the rainy and dry seasons in the Amazon. It could bring extreme temperatures in Europe and the tropics, disrupting agriculture production.

Warming coastal oceans could fuel more intense storms and rainfall. The rising sea level in the North Atlantic means more infrastructure and property damage. A collapsed AMOC poses serious consequences that should not be ignored or underestimated. This critical ocean current needs to be observed and studied more.