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SOES6002, Module A: Modelling
Climate Instability
Lecture 1
Abrupt Change in Thermohaline Circulation and Climate
Jochem Marotzke
Modelling Climate Instability
• Will the THC weaken under GHG increase?
• What would be the climatic consequences
of a THC collapse?
• If the THC weakens dramatically, will it
return to “normal” after GHG concentration
has returned to pre-industrial?
• Could a THC collapse occur much faster
than indicated by the extant models?
• Which, if any, of the models is correct?
• If the THC weakens dramatically, will it
return to “normal” after GHG concentration
has returned to pre-industrial?
• Address with a minimal model of the THC
• National Research Council (R. B. Alley, J.
Marotzke, J. Overpeck, D. Peteet, R. Pielke, Jr., R.
Pierrehumbert, P. Rhines, T. Stocker, L. Talley, and J. M.
Wallace),
2002: Abrupt Climate Change:
Inevitable Surprises. Washington, D.C.,
National Academy Press, 230pp.
If the THC collapses, will it return to “normal”?
Stommel, 1961; Marotzke, 1990, 2000
If the THC collapses, will it return to “normal”?
If the THC collapses, will it return to “normal”?
If the THC collapses, will it return to “normal”?
Modelling Climate Instability (I)
Use a simple model to investigate:
• How is it possible that the thermohaline circulation (THC)
could be so radically different from it is today?
• Could the pattern of today’s global THC be accidental - a
consequence of special initial conditions?
• What is the role of wind-driven transports in all this?
Modelling Climate Instability (II)
Use a simple model to investigate:
• How does an increase in greenhouse gas (GHG)
concentration modify climate?
• Why does the THC weaken under GHG increase?
• How does climate change under a THC collapse?
• If the THC weakens dramatically, will it return to “normal”
after GHG concentration has returned to pre-industrial?
• What is the role of wind-driven transports in all this?