Climate Change and the AMOC

The Older Dryas

  • The Older Dryas was a period of sudden climate cooling caused by the Atlantic Meridional Overturning Circulation (AMOC) tipping point.
  • It interrupted a general warming trend with abrupt cooling.
  • Evidence includes pollen of the alpine flower Dryas octopetala, indicating a shift from pre- and postglacial forests to glacial shrubs and back again.
  • This climate jump was also observed in ice core measurements of CO2CO_2.

AMOC and Freshwater

  • Adding a lot of freshwater to the ocean impacts ocean circulation.

Younger Dryas

  • After the initial flood subsided, the AMOC restarted.
  • A similar event, the Younger Dryas, occurred with another shutdown of the AMOC.

Antarctic Upwelling

  • As the Southern Atlantic warms, the temperature contrast between the equator and the poles can increase, especially if Antarctic waters remain relatively cold.
  • This enhanced gradient can strengthen the westerly winds around Antarctica.
  • Stronger winds push surface waters away from the continent, promoting upwelling of deeper waters to replace them.

Movie Argument

  • The movie suggests that an AMOC shutdown caused past climate cooling, even with increasing CO2CO_2 levels.
  • It posits that if it happened before, it could happen again, leading to an ice age despite global warming.

Observed SST Change (1870–2016)

  • Signs of a slowdown of the AMOC include:

    • Warming around the East coast of the US
    • Cooling of the North North Atlantic
    • Warming of the South Atlantic

  • The North North Atlantic cooling does not stimulate deepwater formation.

AMOC and Sea Surface Temperature (SST)

  • The AMOC pushes warm surface water towards Europe and cooler arctic surface water down the US eastern coast.
  • Weakening or stopping the AMOC would lead to warming around the East coast of the US.

Sterodynamic Sea Level Effect

  • Sterodynamic sea-level variability is due to changes in the ocean's circulation and the accompanying change in temperature and salinity of a regional water mass.

Sea Level and AMOC

  • Sea level data from tide gauges are anti-correlated with the Gulf Stream strength index from satellite altimeter data.
  • The AMOC suppresses some sea-level rise along the Northeast US by maintaining relatively cool waters, thus reducing expansion.
  • If the AMOC weakens, sea levels will rise faster along the East Coast due to warmer waters.
  • Changes in ocean currents lead to changes in local sea level.

Predicted Sterodynamic Sea Level Change

  • Changes in ocean circulation impact relative sea level worldwide.
  • The sterodynamic effect around New York will be positive due to warmer water, while the effect on London will be negative due to less warm water reaching Europe.

CO2CO_2-Doubling Experiment (Model)

  • Warming of the Southern Atlantic Ocean affects the global meridional overturning circulation.
  • The global meridional overturning circulation cycles heat, carbon, oxygen, and nutrients throughout the world ocean.
  • A slowdown could have devastating effects globally.