Lecture on the economic impacts of a slowdown of the thermohaline circulation, Richard Tol, 9 December 2015, Falmer.

1. Shutting down the
thermohaline circulation
David Anthoff
University of California, Berkeley
Francisco Estrada
Universidad Nacional Autónoma de Mexico
Richard S.J. Tol
University of Sussex, Vrije Universiteit Amsterdam,
Tinbergen Institute, CESifo

6. 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

13. WE FEAR THE COLD

14. -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
Welfare-equivalentincomechange(inpercent)
Global warming (in degrees centrigrade)

15. -20
-15
-10
-5
0
5
10
100 1,000 10,000 100,000
Welfare-equivalentincomechange(inpercent)
Income (in 2005 dollar per person per year)

16. -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
Welfare-equivalentincomechange(inpercent)
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

17. 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

18. -6
-5
-4
-3
-2
-1
0
1temperaturechange(degreecentigrade)
Hadley 0.3
Hadley 0.1
BCM 0.1
IPSL 0.1

19. -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
Welfaregain(%income)
Warming (degree centigrade)
Modest warming due
to greenhouse gases,
severe cooling due to
thermohaline circulation
shutdown
Severe warming due
to greenhouse gases,
modest cooling due to
thermohaline circulation
shutdown

20. -4
-2
0
2
4
6
8welfareimpact(percentincome)
Hadley 0.3
Hadley 0.1
BCM 0.1
IPSL 0.1

21. -10
-8
-6
-4
-2
0
2
4
6
8welfareimpact(percentincome)
Hadley 0.3
Hadley 0.1
BCM 0.1
IPSL 0.1

22. 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