Modeling studies consistently project that a large-scale slowdown or collapse of the AMOC would trigger pronounced shifts in global and regional climate. On average, global mean temperatures would drop by approximately 0.5 °C, but this modest global cooling masks stark hemispheric contrasts. In the Northern Hemisphere, particularly over Europe, winters would become markedly colderâby a few degrees [I guess around 3] Celsius in Western Europe and up to 10 °C in northern latitudesâaccompanied by more frequent and intense winter storms and prolonged summer droughts Armstrong McKay et al. (2022), Jackson et al. (2015).
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Full AMOC collapse is projected to unfold over approximately 15 to 50+ years [I guess around 100], as detailed by Armstrong McKay et al. (2022) with slower biophysical processesâsuch as new sea-ice formation extending the tail of the collapse timeline.
The above suggest AMOCâs collapse would decrease temperature in Western Europe by 0.0300 (= 3â100) to 0.200 ÂșC/âyear (= 3â15), and in northern latitudes up to 0.100 (= 10â100) to 0.667 ÂșC/âyear (= 10â15). Given these variations, I guess the probability of the population of Europe decreasing by more than 10 % as a result of AMOCâs collapse would be lower than 0.01 %.
I probably shouldnât have cited the averages like I did here because it hides the seasonal extremes, also itâs really the variance that shows what society will need to contend with if this were to happen. This recent paper by van Westen published just a few weeks ago illustrates the differences in winter/âsummer temps as well as how âunusualâ events will become more frequent. London for example, could face â40C winter weather. https://ââagupubs.onlinelibrary.wiley.com/ââdoi/ââ10.1029/ââ2025GL114611
Curious, how did you calculate your estimate of European population decline?
Thanks for clarifying. I still think the variation in the mean temperature is useful because they constrain the seasonal variation. Each season lasts for 0.25 years (= 1â4), so a season becoming e.g. 10 ÂșC cooler will make the year 2.50 ÂșC (= 0.25*10) cooler. Assuming the effect of AMOCâs collapse on Spring and Summer and is negligible, and that the effect on Autumn and Winter is similar, these would cool 2 (= 4â2) times as fast as I estimated above. So by 0.0600 (= 0.0300*2) to 0.400 ÂșC/âyear (= 0.200*2) in Western Europe, and up to 0.200 (= 0.100*2) to 1.33 ÂșC/âyear (= 0.667*2) in northern latitudes. I know you pointed out that the extremes matter, but I think the seasonal variations are still relevant. At least now, deaths from moderate cold are much larger than from extreme cold.
I did not calculate the probability of the European population decreasing by more than 10 %. I simply speculated it is lower than 0.01 %. For context, the deaths from non-optimal temperature as a fraction of the population in Europe in 2021 were 0.0416 %. The respective death rate across time is below. For the European population to become at least 10 % smaller, that death rate would have to become at least 240 (= 0.1/â(4.16*10^-4)) times as large, which seems a lot considering how little is has varied across time.
Thanks for the explanation! I think I see what youâre saying now. I bet youâre right, deaths attributed to the change in temperature would likely remain low. I think most of the deaths would come from food shortages (as of the current data, a lot of land in Europe would no longer be arable) and that could affect a more significant portion of the population.
You are welcome! The deaths from non-optimal temperature plotted above are supposed to cover all causes of death, including from food shortages (although these might account for a much larger fraction of the deaths from non-optimal temperature for abrupt variations of temperature). There were 1.91 M deaths from non-optimal temperature in 2021, 53.1 (= 1.91*10^6/â(36.0*10^3)) times the 36.0 k deaths from environmental heat and cold exposure. From Our World in Data (OWID):
Think about someone dying from extreme temperatures. You probably pictured someone passing out from heat stroke or dying from hypothermia.
But this is not how most people die from âheatâ. They die from conditions such as cardiovascular or kidney disease, respiratory infections, or diabetes.
Thanks for the post, Rebecca!
The above suggest AMOCâs collapse would decrease temperature in Western Europe by 0.0300 (= 3â100) to 0.200 ÂșC/âyear (= 3â15), and in northern latitudes up to 0.100 (= 10â100) to 0.667 ÂșC/âyear (= 10â15). Given these variations, I guess the probability of the population of Europe decreasing by more than 10 % as a result of AMOCâs collapse would be lower than 0.01 %.
I probably shouldnât have cited the averages like I did here because it hides the seasonal extremes, also itâs really the variance that shows what society will need to contend with if this were to happen. This recent paper by van Westen published just a few weeks ago illustrates the differences in winter/âsummer temps as well as how âunusualâ events will become more frequent. London for example, could face â40C winter weather. https://ââagupubs.onlinelibrary.wiley.com/ââdoi/ââ10.1029/ââ2025GL114611
Curious, how did you calculate your estimate of European population decline?
Thanks for clarifying. I still think the variation in the mean temperature is useful because they constrain the seasonal variation. Each season lasts for 0.25 years (= 1â4), so a season becoming e.g. 10 ÂșC cooler will make the year 2.50 ÂșC (= 0.25*10) cooler. Assuming the effect of AMOCâs collapse on Spring and Summer and is negligible, and that the effect on Autumn and Winter is similar, these would cool 2 (= 4â2) times as fast as I estimated above. So by 0.0600 (= 0.0300*2) to 0.400 ÂșC/âyear (= 0.200*2) in Western Europe, and up to 0.200 (= 0.100*2) to 1.33 ÂșC/âyear (= 0.667*2) in northern latitudes. I know you pointed out that the extremes matter, but I think the seasonal variations are still relevant. At least now, deaths from moderate cold are much larger than from extreme cold.
I did not calculate the probability of the European population decreasing by more than 10 %. I simply speculated it is lower than 0.01 %. For context, the deaths from non-optimal temperature as a fraction of the population in Europe in 2021 were 0.0416 %. The respective death rate across time is below. For the European population to become at least 10 % smaller, that death rate would have to become at least 240 (= 0.1/â(4.16*10^-4)) times as large, which seems a lot considering how little is has varied across time.
Thanks for the explanation! I think I see what youâre saying now. I bet youâre right, deaths attributed to the change in temperature would likely remain low. I think most of the deaths would come from food shortages (as of the current data, a lot of land in Europe would no longer be arable) and that could affect a more significant portion of the population.
You are welcome! The deaths from non-optimal temperature plotted above are supposed to cover all causes of death, including from food shortages (although these might account for a much larger fraction of the deaths from non-optimal temperature for abrupt variations of temperature). There were 1.91 M deaths from non-optimal temperature in 2021, 53.1 (= 1.91*10^6/â(36.0*10^3)) times the 36.0 k deaths from environmental heat and cold exposure. From Our World in Data (OWID):