What would the consequences to humanity actually look like if the AMOC was to shut down?
To try and probe this question, I examine in detail a fascinating peer reviewed paper called “Insights from past millennia into climatic impacts on human health and survival”. Over the past several thousands of years, there have been many different civilizations build up and then very quickly collapse and essentially vanish, and this paper tries to tease out the climate connections to many of these collapses. The nexus of drought-food scarcity-famine seems to be the most common pathway leading to the collapse of many societies.
Abstract
Climate change poses threats to human health, safety, and survival via weather extremes and climatic impacts on food yields, fresh water, infectious diseases, conflict, and displacement. Paradoxically, these risks to health are neither widely nor fully recognized. Historical experiences of diverse societies experiencing climatic changes, spanning multicentury to single-year duration, provide insights into population health vulnerability—even though most climatic changes were considerably less than those anticipated this century and beyond. Historical experience indicates the following.
(i) Long-term climate changes have often destabilized civilizations, typically via food shortages, consequent hunger, disease, and unrest.
(ii) Medium-term climatic adversity has frequently caused similar health, social, and sometimes political consequences.
(iii) Infectious disease epidemics have often occurred in association with briefer episodes of temperature shifts, food shortages, impoverishment, and social disruption.
(iv) Societies have often learnt to cope (despite hardship for some groups) with recurring shorter-term (decadal to multiyear) regional climatic cycles (e.g., El Niño Southern Oscillation)—except when extreme phases occur.
(v) The drought–famine–starvation nexus has been the main, recurring, serious threat to health.
Warming this century is not only likely to greatly exceed the Holocene’s natural multidecadal temperature fluctuations but to occur faster. Along with greater climatic variability, models project an increased geographic range and severity of droughts.
Modern societies, although larger, better resourced, and more interconnected than past societies, are less flexible, more infrastructure-dependent, densely populated, and hence are vulnerable. Adverse historical climate-related health experiences underscore the case for abating human-induced climate change.
Evidence that clearly shows there was large methane clathrate thaw on continental shelves off Africa during the Eeemian Interglacial around 125-126,000 years ago.
The evidence [1] is in the marine core sediment layers on the continental shelf and just outside the shelf in the water column down to 1800 m depths. The sediment core record evidence, using various dating proxies, various types of biologically derived organic proxies, and isotopic analysis give us proof for large methane emission into the water column and oxidation, large atmospheric methane concentrations, and warning of the intermediate water layers by 6.8 C at 700 meters depth (from about 7 degrees C to about 14 degrees C). This warming physically enters deep into the marine sediments destabilizing the methane clathrates, by melting the ice cage and releasing methane gas.
As mentioned in the previous video, in the North Atlantic the subsurface water at 150 meter depth of Newfoundland warmed from about 7 degrees C by between 8 and 12 degrees C, destabilizing the ice sheets and glaciers causing tremendous calving as measured by Ice Rafted Debris (IRD) in Heinrich Events.
In this video, the peer recent reviewed scientific paper shows that intermediate depth water off Africa at 700 meter depth warmed from 7 degrees C by about 6.8 degrees C, destabilizing methane clathrates within the sediment.
Importance for Present Day Climate System:
1) Clearly, with AMOC (Atlantic Meridional Overturning Circulation) the intermediate water will warm significantly, by at least 7 degrees C in both the North Atlantic and equatorial East Atlantic (likely also at many other places; two studies were just scratching the surface).
2) In the North Atlantic, we can expect this warming to greatly destabilize Greenland Ice Sheets and Glaciers grounded below sea level.
3) In the equatorial East Atlantic, this warming destabilized methane sediments within the sea floor sediments, and caused massive outbursts of methane changing global climate.
4) Although not discussed here, I recall a paper from a few years ago by Hansen et. al (and other papers) talking about how intermediate water near Antarctica was warming quickly. We know that Antarctica Ice melt is rapidly accelerating, with a doubling period of about 7 years (as is Greenland Ice melt). Clearly, Greenland Ice is melting from below (by warm ocean water) and on top (by warm air temperatures). However Antarctica is not melting a lot on top (still too cold) so therefore HAS to be melting more and more from below, from warming ocean water.
Sincerely,
Paul
Ref 1: Evidence for massive methane hydrate destabilization during the penultimate interglacial warming. Link, here. Schneider, Yu, Kylander-Clark. Edited by Mark Thiemens, University of California San Diego, La Jolla, CA; received February 3, 2022; accepted July 2, 2022. August 22, 2022
With thanks to:
Paul Beckwith
Well known climate science educator; Part-time Geography professor (climatology, oceanography, environmental issues), University of Ottawa. Physicist. Engineer. Master’s Degree in Science in Laser Optics, Bachelors of Engineering, in Engineering Physics. Won Association of Professional Engineers of Ontario gold medal. Also interested in investment and start-ups in climate solutions, renewable energy and energy efficiency. Avid chess player, and likes restoring old homes. Married with children.