Will the Gulf Stream disappear with global warming…?
description
Transcript of Will the Gulf Stream disappear with global warming…?
![Page 1: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/1.jpg)
Will the Gulf Stream disappear with global warming…?
![Page 2: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/2.jpg)
Strength of ocean overturning at 30N (A1B Scenario + constant after yr2100)
![Page 3: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/3.jpg)
Our own EPcm
After a sudden 2XCO2
Control experiment
![Page 4: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/4.jpg)
Strength of ocean overturning at 30N (A1B Scenario + constant after yr2100)
What is the ocean doing...??
![Page 5: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/5.jpg)
Outline
• Background on the thermohaline circulation and the Gulf Stream
• Why is there such a large spread among climate models when it comes to the Gulf Stream?
• Will the Gulf Stream disappear with global warming?
![Page 6: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/6.jpg)
Part 1: Background on the Gulf Stream and the thermohaline
circulation
![Page 7: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/7.jpg)
Broecker, 2005NB: 1 Amazon River ≈ 0.2 Million m3/s
![Page 8: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/8.jpg)
Broecker, 2005NB: 1 Amazon River ≈ 0.2 Million m3/s
The Gulf Stream refers to the North Atlantic portion of this global “thermohaline circulation”
![Page 9: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/9.jpg)
When was the thermohaline circulation discovered?
![Page 10: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/10.jpg)
Captain Ellis and the Earl of Halifax “measurements” (1751)
• “Upon the passage, I made several trials with the bucket sea-gage. I charged it and let it down to different depths, from 360 feet to 5346 feet; when I discovered, by a small thermometer of Fahrenheit’s, made by Mr. Bird, which went down to it, that the cold increased regularly, in proportion to the depths, till it descended to 3900 feet: from whence the mercury in the thermometer came up to 53 degrees; and tho’ I afterwards sunk it to the depth of 5346 feet, it came up no lower. The warmth of the water upon the surface, and that of the air, was at the time by the thermometer 84 degrees.”
![Page 11: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/11.jpg)
Captain Ellis and the Earl of Halifax “measurements” (1751)
• “The experiment, which seem’d at first but mere food for curiosity, became in the interim very useful to us. By its means we supplied our cold bath, and cooled our wines or water at pleasure; which is vastly agreeable to us in this burning climate”
NB: Captain Ellis was at 25N, 25W
![Page 12: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/12.jpg)
Count Rumford explains the measurements…
born Benjamin Thompson (1753-1814)
But a still more striking, and I might, I believe, say, an incontrovertible proof of the existence of currentsof cold water at the bottom of the Sea, setting fromthe poles towards the equator, is the very remarkabledifference that has been found to subsist betweenthe temperature of the sea at the surface and atgreat depth, at the tropic –though the temperatureof the atmosphere there is so constant that the greatest changes produced in it by the seasonsseldom amounts to more than five or six degrees;yet the difference between the heat of water at thesurface of the Sea, and that at the depth of 3600 feet,has been found to amount to no less than 31 degrees;the temperature above or at the surface being 84 degrees, and at the given depth below no more than 53 degrees.
It appears to me to be extremely difficult, if not quiteimpossible, to account for this degree of cold at the bottom of the sea in the torrid zone, on any other supposition than that of cold currents from the poles.
![Page 13: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/13.jpg)
![Page 14: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/14.jpg)
The “great oceanic conveyor belt”
![Page 15: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/15.jpg)
The “great oceanic conveyor belt”
![Page 16: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/16.jpg)
Theory of the thermohaline circulation also led to observational
discoveries
![Page 17: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/17.jpg)
The Stommel-Aarons-Faller experiments (1958)
WARM
COLD
Surface cooling
Volume of cold layerincreases at the expenseof the volume of warm water
WaterSo
So
Ω
![Page 18: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/18.jpg)
Results
SoA “western boundary current” is produced,flowing towards the “South” (equator)!
“West” “East”
“South”
“North”
![Page 19: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/19.jpg)
Results
SoA “western boundary current” is produced,flowing towards the “South” (equator)!
“West” “East”
“South”
“North”
This deep current was observed in the North Atlantic in 1960
![Page 20: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/20.jpg)
More recent measurementsof Deep Western Boundary currents in the North Atlantic
Meinen et al. (2004)
Subtropical gyrecurrent (northward)
Deep westernBoundary current
(southward)
![Page 21: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/21.jpg)
“Observations” of the Gulf Stream
and the thermohaline circulation
![Page 22: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/22.jpg)
No such observations can exist…
• Impossible to have current meters everywhere in the ocean at any time!
• So one needs to be smart and interpolate the available data in the best possible way…
• To do this the solution is to constrain a numerical ocean model to be close to observations
![Page 23: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/23.jpg)
Sea surface height measured from Space
![Page 24: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/24.jpg)
Why is sea surface height useful?
… Newton’s law!
CORIOLIS FORCE = PRESSURE FORCE
Current Sea surface height
![Page 25: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/25.jpg)
10-yr average sea surface height (deviation from geoid)
![Page 26: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/26.jpg)
10-yr average sea surface height (deviation from geoid)
GULF STREAM
![Page 27: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/27.jpg)
![Page 28: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/28.jpg)
![Page 29: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/29.jpg)
KUROSHIO GULF STREAM
AGULHASEast Australian Current
Malvinas
![Page 30: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/30.jpg)
Sv2010max
Atlantic ocean’s meridional overturning streamfunction simulated by MITgcm constrained to satellite altimetry
136101 smSv
Wunsch (2000)
![Page 31: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/31.jpg)
Part 2: Mechanisms
• Why is there so much spread among climate models?
![Page 32: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/32.jpg)
Mechanisms
• Why is there so much spread among climate models?
→ Feedback analysis!
![Page 33: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/33.jpg)
Stommel’s model of the thermohaline circulation (1961)
1 2
Heating & Salinification
(low latitudes)
Cooling & Freshening(high latitudes)
)( 21 k
)1( STo
z
(Anticlockwise if box1 is denser)
(density increases with S &decreases with T)
temperature salinity
“sea surface”
“Gulf Stream”
![Page 34: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/34.jpg)
Heating and cooling at the sea surface
Surface heat flux (Wm-2, color) and temperature (contours, °C) -NOC climatology
Cooling: Enthalpy flux+surface radiation exceed solar+greenhouseradiation
Heating:Solar+greenhouse radiation exceedEnthalpy flux+surfaceradiation
![Page 35: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/35.jpg)
Net Evaporation minus Precipitation
![Page 36: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/36.jpg)
Two equilibrium states
WARM(salty)
COLD(fresh)
“Thermal”:-Density driven by T-Strong Gulf Stream
Ψ
High latitudesLow latitudes
SALTY(warm)
FRESH(cold)
High latitudesLow latitudes
Ψ“Haline”:
-Density driven by S -Weak (reverse) Gulf
Stream
![Page 37: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/37.jpg)
Positive salt feedbackHigh S at
high latitudes
Enhanced N/Sdensity gradient
Enhanced GulfStream
![Page 38: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/38.jpg)
Positive salt feedbackHigh S at
high latitudes
Enhanced N/Sdensity gradient
Enhanced GulfStream
UNSTABILITY, leads tolarge response to
perturbations
![Page 39: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/39.jpg)
Low T at high latitudes
Negative temperature feedbackHigh T at
high latitudes
Reduced N/Sdensity gradient
Reduced GulfStream
(reduced polewardheat transport)
![Page 40: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/40.jpg)
Low T at high latitudes
Negative temperature feedbackHigh T at
high latitudes
Reduced N/Sdensity gradient
Reduced GulfStream
(reduced polewardheat transport)
STABILITY, leads tosmall response to
perturbations
![Page 41: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/41.jpg)
Different models have different temperature & salinity feedbacks
and this is what leads to the spread in models’ behaviour
![Page 42: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/42.jpg)
Different models have different temperature & salinity feedbacks because these involve coupled ocean-atmosphere processes…
• Changes in sea surface temperature induced by changes in ocean circulation alter the atmospheric circulation
• This in turn modifies the cooling and freshening of the ocean at the sea surface…
• … which changes back the sea surface temperature and salinity!
![Page 43: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/43.jpg)
Inter-model comparison is a very active area of research…
100yr 200yr 300yrOce
an c
ircul
atio
n in
tens
ity
Strong Sfeedback because ofweak A/Ocoupling…
Yin & Stouffer (2007)
![Page 44: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/44.jpg)
Part 3: Will the Gulf Stream disappear with global warming?
![Page 45: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/45.jpg)
Strength of ocean overturning at 30N (A1B Scenario + constant after yr2100)
![Page 46: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/46.jpg)
…pushing the limit:a movie scenario…?
Movie Scenario:
-CO2 increases-Hydrological cycle strengthens-Atlantic Ocean becomes much less salty-The heat pump structure breaks down: the mechanical energy input by the wind can not be converted to a heat transport-Sea-ice margin moves southward-Sea-ice albedo kicks in… Global Freeze!
![Page 47: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/47.jpg)
The answer is no
• As a result of increased CO2, more freshening and more surface heating, which indeed reduces the high latitude density
![Page 48: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/48.jpg)
The answer is no
• As a result of increased CO2, more freshening and more surface heating, which indeed reduces the high latitude density
• No model predicts an abrupt switch to an “off-state” within the 21st century
![Page 49: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/49.jpg)
The answer is no
• As a result of increased CO2, more freshening and more surface heating, which indeed reduces the high latitude density
• No model predicts an abrupt switch to an “off-state” within the 21st century
• The models which predict a significant weakening are the least reliable (very elementary atmospheric feedbacks, “flux adjusted”)
![Page 50: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/50.jpg)
The answer is no• As a result of increased CO2, more freshening
and more surface heating, which indeed reduces the high latitude density
• No model predicts an abrupt switch to an “off-state” within the 21st century
• The models which, predict a significant weakening are the least reliable (very elementary atmospheric feedbacks, “flux adjusted”)
• In general, the more complex the model, the more stable the Gulf Stream
![Page 51: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/51.jpg)
Conclusions
• A lot of work needs to be done on modelling the ocean circulation and its interaction with the atmosphere
• The Gulf Stream will not disappear with Global Warming!
![Page 52: Will the Gulf Stream disappear with global warming…?](https://reader035.fdocuments.in/reader035/viewer/2022062814/568167bd550346895ddd0d5d/html5/thumbnails/52.jpg)
…I leave it to Jenny…
But I maintain office hours until the end of term:
Tuesdays, 1-2pm in HuxleyRoom 726