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Fresh water pouring into the North Atlantic is what will shut down the Gulf Stream, plunging northern and western Europe into a far colder climate more typical

Fresh water pouring into the North Atlantic is what will shut down the Gulf Stream, plunging northern and western Europe into a far colder climate more typical for their latitude. Yeah, you’d think this would be bigger news. See also Warning Signals for Collapse of the Atlantic Meridional Overturning Circulation, Nature, 2 weeks ago (good discussion that got shut down as a duplicate, although it’s the primary source paper and all the rest were secondary, but whatever, bots or something): https://news.ycombinator.com/item?id=28085342 https://news.ycombinator.com/item?id=28085342

chrisco255 5y ago
We don't control the AMOC or any other oceanic cycle, including the AMO, PDO, ENSO, etc. If the AMOC reduces circulation, then the planet will cool as a whole, and we'll probably find ourselves retreading into a Little Ice Age, as experienced from the 1400s to mid 1800s. At any rate that would be counter to the projections of runaway warming.
- jazzyjackson 5y ago
  Why does reduced circulation cool the planet as a whole? I would expect the heat to stay where it’s hot in the tropics and the cool to stay where it’s cold in the poles, with hurricanes and tornadoes making up the vortexful barrier between them, but iana fluid dynamicyst
  - Kaibeezy 5y ago
    IIRC, when the Arctic stays cold, there’s more sea ice, which reflects more sunlight than open water, reducing total/overall temperatures. ETA: The sea is dark; the ice is white. That makes a big difference when it comes to reflecting sunlight. The dark sea absorbs heat while the ice reflects a much larger proportion of the sun’s energy (the “Albedo-effect”). So a smaller sea ice extent means more open, dark water, which results in more absorption of the sun’s energy in the seawater, and thus more warming of the seawater. The warmer seawater raises the temperature of the air above, which means that ice formation will take place later in the year. And next year, when melting sets in, there is less ice and melting may happen faster, which means that the sea is open to absorb even more energy from the sun. And so on. Scientists call it a positive feedback that enhances the changes even further. And this specific feedback has been documented in the Arctic. To what degree this will have effects outside the Arctic is still an open question. The diminishing sea ice also has the potential to change global ocean circulation. In the Arctic Ocean, especially east of Greenland, a process takes place that is considered to be crucial for the circulation of the oceans. As the waters flowing north to this area cool, sea ice forms; leaving the water below the ice much saltier and denser. This heavier water sinks to the bottom and flows south along the deep plains of the Atlantic Ocean. The force of this, in combination with similar processes in Antarctica, is so tremendous that these mechanisms actually fuel global ocean circulation. The cold water follows the bottom of the Atlantic, resurfaces, for instance, in the Indian Ocean and returns as a warm ocean surface current in the Atlantic Ocean, commonly known as “The Gulf Stream”. The system is often referred to as “The Great Conveyor Belt”. To what extent “The Great Conveyor Belt” will be affected by the diminishing Arctic sea ice is still an open question. http://polarportal.dk/en/sea-ice-and-icebergs/understanding-the-arctic-sea-ice/ http://polarportal.dk/en/sea-ice-and-icebergs/understanding-...
    - lmilcin 5y ago
      The issue is the Arctic is not likely to re-freeze even with Gulf Stream gone. This is a little bit like bi-stable switch. Once it switches one way it wants to be in that position until there is enough force to push it the other way.
      - Kaibeezy 5y ago
        I see what you’re saying. The Gulf Stream affects ocean water distribution worldwide, but doesn’t necessarily have much affect on the Arctic Ocean itself.
        lmilcin 5y ago
        Of course it makes it a little warmer, but the point is, the most important factor that makes Arctic Ocean... well... arctic... is whether it reflects sunlight or not. Water is dark and accepts a lot of sun's energy, getting warmer. With ice present it reflects a lot of that energy back to space. The amount of energy difference we are talking about is astounding. The Gulf Stream, as large as it is, pales in comparison to the amount of sunlight reflected by patch of snow the size of entire Arctic Ocean. Now, I don't want to say Gulf Stream is insignificant. It will definitely have huge effect, especially on Europe where I live. The most important effect, per my understanding, is less rainfall. Because that warm water vaporizes and those vapors tend to turn to rain/snow over Europe. Shift in wind patterns I don't understand so can't elaborate.
        chrisco255 5y ago
        If the water goes below freezing temperatures, it will tend to freeze and turn white. If the hot tropics are currently pulling warm water up towards the Arctic via the AMOC, the average water temperature of the Arctic is increased. If that pattern were to decrease, you would get colder Arctic water that tends to freeze more easily. A lot of ocean water is already covered by something else with albedo: clouds. Particularly in the poles, clouds tend to form very easily. Reduced AMOC circulation is associated with dramatic effects in the past for Earth's climate. "The Little Ice Age was one of the coldest periods of the last ~10,000 years in the Northern-Hemisphere. Although there is increasing evidence that this cooling was associated with a weakening of the Atlantic Meridional Overturning Circulation (AMOC), the sequence of events that led to a significant reduction in deep convection has yet to be explained." https://instaar.colorado.edu/meetings/AW2021//abstract_details.php?abstract_id=53 https://instaar.colorado.edu/meetings/AW2021//abstract_detai...
  - chrisco255 5y ago
    The northern hemisphere has an outsized effect on global temperatures, because there's more land area in the northern hemisphere. As mentioned in other comments, albedo (reflectivity) from sea ice (as well as clouds) reduces solar input into the Earth climate system. But also, more importantly, land ice and snow extent also can have an effect on Earth's average albedo. If less warm water from the tropics is being pulled up towards the Arctic via the AMOC, not only will sea ice form more easily, but temperatures will tend to stay colder in northern latitudes in North America and Europe in particular, which is conducive for longer winters, great chance of standing snow cover, etc. "Crippled Atlantic currents triggered ice age climate change" https://www.sciencemag.org/news/2016/06/crippled-atlantic-currents-triggered-ice-age-climate-change https://www.sciencemag.org/news/2016/06/crippled-atlantic-cu... "What Caused the Younger Dryas Cold Event?" https://pubs.geoscienceworld.org/gsa/geology/article/38/4/383/130267/What-Caused-the-Younger-Dryas-Cold-Event https://pubs.geoscienceworld.org/gsa/geology/article/38/4/38...

chrisco255 5y ago

We don't control the AMOC or any other oceanic cycle, including the AMO, PDO, ENSO, etc. If the AMOC reduces circulation, then the planet will cool as a whole, and we'll probably find ourselves retreading into a Little Ice Age, as experienced from the 1400s to mid 1800s. At any rate that would be counter to the projections of runaway warming.

jazzyjackson 5y ago
Why does reduced circulation cool the planet as a whole? I would expect the heat to stay where it’s hot in the tropics and the cool to stay where it’s cold in the poles, with hurricanes and tornadoes making up the vortexful barrier between them, but iana fluid dynamicyst
- Kaibeezy 5y ago
  IIRC, when the Arctic stays cold, there’s more sea ice, which reflects more sunlight than open water, reducing total/overall temperatures. ETA: The sea is dark; the ice is white. That makes a big difference when it comes to reflecting sunlight. The dark sea absorbs heat while the ice reflects a much larger proportion of the sun’s energy (the “Albedo-effect”). So a smaller sea ice extent means more open, dark water, which results in more absorption of the sun’s energy in the seawater, and thus more warming of the seawater. The warmer seawater raises the temperature of the air above, which means that ice formation will take place later in the year. And next year, when melting sets in, there is less ice and melting may happen faster, which means that the sea is open to absorb even more energy from the sun. And so on. Scientists call it a positive feedback that enhances the changes even further. And this specific feedback has been documented in the Arctic. To what degree this will have effects outside the Arctic is still an open question. The diminishing sea ice also has the potential to change global ocean circulation. In the Arctic Ocean, especially east of Greenland, a process takes place that is considered to be crucial for the circulation of the oceans. As the waters flowing north to this area cool, sea ice forms; leaving the water below the ice much saltier and denser. This heavier water sinks to the bottom and flows south along the deep plains of the Atlantic Ocean. The force of this, in combination with similar processes in Antarctica, is so tremendous that these mechanisms actually fuel global ocean circulation. The cold water follows the bottom of the Atlantic, resurfaces, for instance, in the Indian Ocean and returns as a warm ocean surface current in the Atlantic Ocean, commonly known as “The Gulf Stream”. The system is often referred to as “The Great Conveyor Belt”. To what extent “The Great Conveyor Belt” will be affected by the diminishing Arctic sea ice is still an open question. http://polarportal.dk/en/sea-ice-and-icebergs/understanding-the-arctic-sea-ice/ http://polarportal.dk/en/sea-ice-and-icebergs/understanding-...
  - lmilcin 5y ago
    The issue is the Arctic is not likely to re-freeze even with Gulf Stream gone. This is a little bit like bi-stable switch. Once it switches one way it wants to be in that position until there is enough force to push it the other way.
    - Kaibeezy 5y ago
      I see what you’re saying. The Gulf Stream affects ocean water distribution worldwide, but doesn’t necessarily have much affect on the Arctic Ocean itself.
      - lmilcin 5y ago
        Of course it makes it a little warmer, but the point is, the most important factor that makes Arctic Ocean... well... arctic... is whether it reflects sunlight or not. Water is dark and accepts a lot of sun's energy, getting warmer. With ice present it reflects a lot of that energy back to space. The amount of energy difference we are talking about is astounding. The Gulf Stream, as large as it is, pales in comparison to the amount of sunlight reflected by patch of snow the size of entire Arctic Ocean. Now, I don't want to say Gulf Stream is insignificant. It will definitely have huge effect, especially on Europe where I live. The most important effect, per my understanding, is less rainfall. Because that warm water vaporizes and those vapors tend to turn to rain/snow over Europe. Shift in wind patterns I don't understand so can't elaborate.
        chrisco255 5y ago
        If the water goes below freezing temperatures, it will tend to freeze and turn white. If the hot tropics are currently pulling warm water up towards the Arctic via the AMOC, the average water temperature of the Arctic is increased. If that pattern were to decrease, you would get colder Arctic water that tends to freeze more easily. A lot of ocean water is already covered by something else with albedo: clouds. Particularly in the poles, clouds tend to form very easily. Reduced AMOC circulation is associated with dramatic effects in the past for Earth's climate. "The Little Ice Age was one of the coldest periods of the last ~10,000 years in the Northern-Hemisphere. Although there is increasing evidence that this cooling was associated with a weakening of the Atlantic Meridional Overturning Circulation (AMOC), the sequence of events that led to a significant reduction in deep convection has yet to be explained." https://instaar.colorado.edu/meetings/AW2021//abstract_details.php?abstract_id=53 https://instaar.colorado.edu/meetings/AW2021//abstract_detai...
- chrisco255 5y ago
  The northern hemisphere has an outsized effect on global temperatures, because there's more land area in the northern hemisphere. As mentioned in other comments, albedo (reflectivity) from sea ice (as well as clouds) reduces solar input into the Earth climate system. But also, more importantly, land ice and snow extent also can have an effect on Earth's average albedo. If less warm water from the tropics is being pulled up towards the Arctic via the AMOC, not only will sea ice form more easily, but temperatures will tend to stay colder in northern latitudes in North America and Europe in particular, which is conducive for longer winters, great chance of standing snow cover, etc. "Crippled Atlantic currents triggered ice age climate change" https://www.sciencemag.org/news/2016/06/crippled-atlantic-currents-triggered-ice-age-climate-change https://www.sciencemag.org/news/2016/06/crippled-atlantic-cu... "What Caused the Younger Dryas Cold Event?" https://pubs.geoscienceworld.org/gsa/geology/article/38/4/383/130267/What-Caused-the-Younger-Dryas-Cold-Event https://pubs.geoscienceworld.org/gsa/geology/article/38/4/38...