Gulf Stream Slowing

Aug. 6, 2021

Two tipping points related to climate change that worry me the most are the addition of methane to the atmosphere from the warming of the permafrost at high latitudes and effect of climate change on the ocean currents in the Atlantic. We already know the heatwaves of the past two summers have led to worrying amounts of methane being released into the atmosphere. Now, a recent study published in the Nature Climate Change journal is raising concerns about ocean current circulation in the Atlantic. Climate scientists have detected warning signs of the collapse of the Gulf Stream, one of the planet’s main potential tipping points toward irreparable changes in the environment. Climate models have shown that the AMOC (Atlantic Meridional Overturning Circulation) is at its weakest in more than 1000 years.

Such an event would have catastrophic consequences around the world, severely disrupting the rains that billions of people depend on for food in India, South America and West Africa; increasing storms and lowering temperatures in Europe; and pushing up the sea level off eastern North America. It would also further endanger the Amazon rainforest and Antarctic ice sheets.

“The signs of destabilization being visible already is something that I wouldn’t have expected and that I find scary,” said Niklas Boers, from the Potsdam Institute for Climate Impact Research in Germany, who did the research. “It’s something you just can’t [allow to] happen.”

Basically, the Gulf Stream brings warm tropical waters to the north Atlantic. When the warm water cools, its density increases and it sinks. The northern branch of the Gulf Stream, the North Atlantic Current, is deeper and is caused by thermohaline circulation resulting from density differences in the water. In other words, the density of the water is affected by temperature and the amount of salt in the water. Melting of ice at high latitudes decreases salinity with the addition of freshwater. Warmer temperatures also affect the current. And this current has a huge impact on weather and climate in the northern Atlantic, Europe, the eastern seaboard of the US and Canada. Additionally, the Gulf Stream is important to the distribution of wildlife in the Atlantic. The waters off of Nantucket, Massachusetts, for example, are incredibly biodiverse because the presence of the Gulf Stream makes it the northern limit for southern species varieties and the southern limit for northern species.

By analyzing the sea-surface temperature and salinity patterns of the Atlantic Ocean, the study said the weakening of the last century is likely to be associated with a loss of stability of the current.

"The findings support the assessment that the AMOC decline is not just a fluctuation or a linear response to increasing temperatures but likely means the approaching of a critical threshold beyond which the circulation system could collapse," Boers said.

If the AMOC collapsed, it would increase cooling of the Northern Hemisphere, sea level rise in the Atlantic, an overall fall in precipitation over Europe and North America and a shift in monsoons in South America and Africa, Britain's Met Office said.

This is just one study and this important topic will require more investigation because there are so many variables that need to be explored. But, it is more evidence that humans are upsetting the climate and environmental conditions under which current organisms have thrived.

Observation-based early-warning signals for a collapse of the Atlantic Meridional Overturning Circulation by Niklas Boers in NATURE CLIMATE CHANGE | VOL 11 | AUGUST 2021 | 680–688 | www.nature.com/natureclimatechange