AMOCMIP: Probabilistic projections of future AMOC evolution driven by global warming and

Greenland Ice Sheet melt

AMOCMIP: Probabilistic projections of future AMOC evolution driven by global warming and

Greenland Ice Sheet melt

Pepijn Bakker1

A. Abe-Ouchi2, D. Bi3, M. van den Broeke4, A. Hu5, J. Lenaerts4, R. Lynn Beadling6, S. Marsland3, S.H. Mernild7, R. Ohgaito2, C. Rodehacke8, O. Saenko9, D.

Swingedouw10, A. Schmittner1, S. Yang8, J. Yin6

1) Oregon State University 2) Japan Agency for Marine-Earth Science Technology 3) CSIRO Marine & Atmospheric Research 4) Institute for

Marine and Atmospheric research, Utrecht University 5) National Center for Atmospheric Research 6) University of Arizona 7) Center for Scientific

Studies, Chile 8) Danish Meteorological Institute 9) Canadian Centre for Climate Modelling and Analysis 10) Institut Pierre-Simon Laplace

IPCC reports 21st century AMOC weakening by:● 20-30% for RCP4.5● 36-44% for RCP8.5

However:

→ Melt of Greenland Ice Sheet (GIS) not considered

→ No thorough analysis of uncertainty related to:

● Model dependent AMOC sensitivity● Climate sensitivity● Regional temperature changes● Rate of GIS melt

● AMOCMIP:

Model intercomparison of IPCC-type global climate models forced by identical and realistic changes in GHGs and GIS melt run until 2300.

GCMs currently included:

● CanESM2 (RCP4.5 + RCP8.5)

● CCSM4 (RCP4.5 + RCP8.5)

● CESM (RCP4.5 + RCP8.5)

● IPSL (RCP4.5)

● GFDL (RCP8.5)

● OSUVic (RCP4.5 + RCP8.5)

Still to be included:

● MIROC

● EC-Earth

● ACCESS

● GISS

GIS melt forcing scenarios:● → High-resolution (11km) atmospheric climate model for Greenland

(RACMO2) including complex snow physics

– →

→ Combined with CMIP5 Multi-Model-Mean temperature projections yields projections of GIS melt including spatial dependency and strong seasonal cycle

→ Note that changes in ice-berg calving are ignored

12

3

45

6

7

8

Lenaerts et al. (2015)

Rr=f (ΔT r500 hPa)

● AMOCMIP results:

●

In order to assess the impact of uncertainty in:● Model dependent AMOC sensitivity● Climate sensitivity● Regional temperature changes● Rate of GIS melt

We will use a physics-based box-model as an AMOC emulator

● AMOC emulator:

Atmosphere

Ocean

Extension of Stommel (1961) and Zickfeld et al. (2004)

● AMOC emulator:

Atmosphere

Ocean

AMOC=k (ρ3−ρ1)

Extension of Stommel (1961) and Zickfeld et al. (2004)

● AMOC emulator:

Atmosphere

Ocean

Forcings

Extension of Stommel (1961) and Zickfeld et al. (2004)

● AMOC emulator:

Simulated annealing is used to tune 7 free parameters.

● Resulting AMOC emulators capture main characteristics of the AMOC's sensitivity to temperature and GIS melt changes of a particular GCM

rical noGIS GISmelt noGIS GISmeltHisto- RCP4.5 RCP4.5 RCP8.5 RCP8.5

AM

OC

str

en

gth

(S

v)

AMOC emulator:

Physics-based box-model to assess combined uncertainty in AMOC projections caused by:

● Model dependent AMOC sensitivity:● 6 GCMs x 10 best AMOC emulator fits → 60 emulators

● Regional temperature changes:● CMIP5-based Gaussian distribution of regional temperature

changes● Rate of GIS melt:

● CMIP5-based Gaussian distribution of temperature changes over Greenland

● Uncertainty in GIS runoff ~ T500hPa relationship

Combine all uncertainties in 10,000 simulations

● AMOC projections:

RCP4.5 (median, 90%-range):● 2100: -18% (-10% to -30%)● 2300: -25% (-12% to -42%)

RCP8.5 (median, 90%-range):● 2100: -36% (-15% to -64%)● 2300: -71% (-17% to -100%)

● AMOC projections:

● AMOC projections:

0.0023 K/GtC (IPCC-2013)

● AMOC projections:

50%

10%

1%

-16%

-27%

-34%

0.0023 K/GtC (IPCC-2013)

Summary:

– → First model intercomparison of future AMOC evolution driven by GHG increases and realistic GIS melt

– → AMOC projected to weaken by 18% (36%) by the year 2100 for RCP4.5 (RCP8.5).

– → AMOC projected to weaken by 25% (71%) by the year 2300 for RCP4.5 (RCP8.5).

– → Impact GIS melt on top of global warming is small

● → Though non-negligible (RCP8.5 at 2300 from 50% to 70% median weakening)

● → Strongly model-dependent● → GIS melt increases probability of AMOC collapse in RCP8.5

– → If global temperature change stays below 2°C, the chance of experiencing a large AMOC weakening is very small

AMOCMIP: Probabilistic projections of future AMOC evolution driven by global warming and Greenland Ice Sheet melt

Questions?

AMOCMIP: Probabilistic projections of future AMOC evolution driven by global warming and Greenland Ice Sheet melt

Questions?

Pepijn Bakker

A. Abe-Ouchi, D. Bi, M. van den Broeke, A. Hu, J. Lenaerts, R. Lynn Beadling, S. Marsland, S.H. Mernild, R. Ohgaito, C. Rodehacke, O. Saenko, D. Swingedouw, A.

Schmittner, S. Yang, J. Yin

Seasonal rangeAdditional slides

Seasonal range

GIS melt forcing scenarios:

Seasonalrange & annual mean

● AMOC emulator:

Atmosphere

Ocean

Extension of Stommel (1961) and Zickfeld et al. (2004)

Fi=f(F

0i+h

i*ΔTglob)