SOES6002, Module A: Modelling Climate Instability

Lecture 1

Abrupt Change in Thermo-haline Circulation and Climate

Jochem Marotzke

• 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?

Modelling Climate Instability

• 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.

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”?

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?