Shutting down the thermohaline circulation

David AnthoffUniversity of California, Berkeley

Francisco EstradaUniversidad Nacional Autónoma de Mexico

Richard S.J. TolUniversity of Sussex, Vrije Universiteit

Amsterdam, Tinbergen Institute, CESifo

Key concern• Climate change could lead to• More rain over the North Atlantic• Melting of the Greenland Ice Sheet

• This would lead to a drop in salinity and may slow-down – or even shut-down – the thermohaline circulation

WE FEAR THE COLD

-25.0

-22.5

-20.0

-17.5

-15.0

-12.5

-10.0

-7.5

-5.0

-2.5

0.0

2.5

5.0

-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5

Wel

fare

-equ

ival

ent i

ncom

e ch

ange

(in

perc

ent)

Global warming (in degrees centrigrade)

-20

-15

-10

-5

0

5

10

100 1,000 10,000 100,000

Wel

fare

-equ

ival

ent i

ncom

e ch

ange

(in

perc

ent)

Income (in 2005 dollar per person per year)

-25.0

-22.5

-20.0

-17.5

-15.0

-12.5

-10.0

-7.5

-5.0

-2.5

0.0

2.5

5.0

-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5

Wel

fare

-equ

ival

ent i

ncom

e ch

ange

(in

perc

ent)

Global warming (in degrees centrigrade)

Fit same function per country:

Optimum temperature:0.3K, range -3 - +7K above today

Slopes vary from zero to 28%Y/K

Hosing• Coupled atmosphere-ocean general

circulation models project a slight weakening of the thermohaline circulation• The impact of a more drastic weakening

are studied using so-calling hosing experiments, in which a Death Star suddenly appears to spout freshwater into the North Atlantic

-6

-5

-4

-3

-2

-1

0

1te

mper

atur

e cha

nge (

degr

ee ce

ntigr

ade)

Hadley 0.3Hadley 0.1BCM 0.1IPSL 0.1

-7

-6

-5

-4

-3

-2

-1

0

1

-3 -2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

Welf

are ga

in (%

incom

e)

Warming (degree centigrade)

Modest warming dueto greenhouse gases,severe cooling duetothermohaline circulationshutdown

Severe warming dueto greenhouse gases,modest cooling duetothermohaline circulationshutdown

-4

-2

0

2

4

6

8w

elfa

re im

pact

(per

cen

t inc

ome)

Hadley 0.3Hadley 0.1BCM 0.1IPSL 0.1

-10

-8

-6

-4

-2

0

2

4

6

8we

lfare

impa

ct (p

er ce

nt in

come

)

Hadley 0.3Hadley 0.1BCM 0.1IPSL 0.1

Wrap-up• Warming is bad, cooling is worse• The cooling due to a shut- or slowdown of

the thermohaline circulation is modest relative to the warming that would induce that.• Reduced warming would lead to a welfare

gain in most countries