The Collapse of AMOC
I am going to briefly interrupt our series in order to talk about a current event that has been all over the news and social media. In a way this is a good thing because it's bringing the climate discussion home, and the coverage has been uniformly good if perhaps a little alarmist (I know, pot calling kettle and all), but it's also an immensely complicated issue. Luckily, this is one we've talked about before, just primarily in the context of another kind of disaster.
In the past I have discussed the collapse of the Atlantic Meridional Overturning Circulation mostly in reference to how the death of an ocean (or portion thereof) can breed a really horrific batch of bacteria that multiply and poison the water and air around it, eventually exacerbating the apocalypse of which, we would by then, already be in the midst. This dead, poison-breathing ocean is called a Canfield Ocean, and it's part of the driver of the planet's worst extinction event (so far).
But the news that we may be scant years from the collapse of AMOC isn't just worrisome because it has the potential to create a Canfield Ocean. AMOC is a major circulator of water, connected to other conveyors of water across the globe, and its collapse–though it has happened many a time before in prehistory–does not bode well for people or anything else.
What is the AMOC and Why is It Important?
The AMOC is a circulatory system of water dependent upon gradients in temperature and salinity, with warm water drifting northward close to the surface and cold water drifting south at much greater depths. As water flows from the surface to the depths, it also circulates a great deal of oxygen to what would otherwise become stagnant waters–making it critical to ocean life. Climate change, broadly warming everything, is slowing AMOC by wrecking the temperature gradient and also by melting ice from the Greenland ice sheet, which dumps fresh water into the ocean and thus dilutes salinity.
The circulation of warm water to northern regions by AMOC has been critical for the development of, well, people, as it greatly improves the climate of the northern reaches of the eastern United States, Canada, as well as the UK and Europe. If you look at Europe on a map, you'll note much of it is farther north than seemingly analogous points in the United States–the reason temperatures are relatively similar is entirely due to AMOC. Without it, the northern climes could chill by 5-10°C. Additionally, Europe would be much drier through the summer months, and between the colder weather and lack of rainfall, this could mean significant crop failure.
In addition, the movement of AMOC pulls a lot of water off the East Coast. A weakening circulation allows that water to flow back, and a collapse will raise the ocean level up to twenty inches across the coast. That's twenty inches gratis, with no input from traditional sea level rise–meaning that particular check would still be in the mail. Twenty inches may not seem like a terrible lot, but it is plenty for communities that are already flooding, already experiencing infrastructure failure during tidal events, and of course getting inundated during hurricane season. All of these will be greatly exacerbated by such a rise.
Lastly
The potential for AMOC's collapse would, in a somewhat just world, be the alarm bell that gets us all working together to stop climate change. This has been a horrific summer in a horrific year and likely the best of the rest of our lives, melting-face-emoji. But, of course, I am highly skeptical of any government being moved to act by such a possibility. Instead, this should galvanize you and yours to action. A post-AMOC world is much more difficult to live in, and we need to ready for that.
I want to say, before I sign off, that the study that made all these headlines is just one study, and not without possibility of error. And while pinning a date like 2025 to such an event is perhaps unwise, it should not in any way obfuscate the truth of the matter: with climate change unchecked, AMOC will collapse. It's a when, not an if.