Ocean Response to Global WarmingOcean Response to Global Warming

William Curry

Woods Hole Oceanographic Institution

Wallace Stegner CenterMarch 3, 2006

What is the Ocean’s Role in Climate?What is the Ocean’s Role in Climate?

• the ocean covers 70% of the earth’s surfacethe ocean covers 70% of the earth’s surface• the ocean stores a thousand times more heat the ocean stores a thousand times more heat

than the atmospherethan the atmosphere• seawater stores four times more heat per unit seawater stores four times more heat per unit

mass than airmass than air• it transports 25 to 50% of the energy received it transports 25 to 50% of the energy received

from the sunfrom the sun

What is the Ocean’s Role in Climate?What is the Ocean’s Role in Climate?

• it circulates slowly, on time scales of decades it circulates slowly, on time scales of decades to centuriesto centuries

• it is the major source of heat to some regions it is the major source of heat to some regions like the North Atlanticlike the North Atlantic

• it sets long-term patterns of atmospheric it sets long-term patterns of atmospheric circulation affecting climate systems like circulation affecting climate systems like ENSO, NAOENSO, NAO

Equator to Pole Heat TransportEquator to Pole Heat Transport

How will the Oceans Change How will the Oceans Change as the Earth Warms?as the Earth Warms?

• the oceans will warm, sea level will risethe oceans will warm, sea level will rise

• its salinity balance will be alteredits salinity balance will be altered

• its ability to absorb COits ability to absorb CO2 2 will changewill change

• it will impact atmospheric circulation, storm it will impact atmospheric circulation, storm tracks, severe storms, and the frequency and tracks, severe storms, and the frequency and distribution of droughtsdistribution of droughts

Levitus et al., 2000Levitus et al., 2000

The oceans The oceans have been have been warming for warming for the last 50 the last 50 yearsyears

The net warming above 3000 m is 0.06The net warming above 3000 m is 0.06oo C C

The oceans have absorbed about 30 times more The oceans have absorbed about 30 times more heat than the atmosphere since 1955heat than the atmosphere since 1955

OceansOceans 18.2 x 1018.2 x 102222 J JAtmosphereAtmosphere 6.6 x 10 6.6 x 102121 J J

Indistinguishable from the expected response to Indistinguishable from the expected response to rising COrising CO2 2 – an anthropogenic signal– an anthropogenic signal

Levitus et al., 2001Levitus et al., 2001

The oceans will continue to absorb heat as The oceans will continue to absorb heat as the climate system warmsthe climate system warms

Warming will cause sea water to expandWarming will cause sea water to expand

The effect of ocean heat absorption will be The effect of ocean heat absorption will be to delay the warming of the atmosphereto delay the warming of the atmosphere

The rate and magnitude of global warming The rate and magnitude of global warming will be affected by how the ocean circulates will be affected by how the ocean circulates in the future – when and where will it in the future – when and where will it release the stored heat?release the stored heat?

What are the Implications?What are the Implications?

What about Salinity?What about Salinity?

• Oceans contain 97% of Earth’s waterOceans contain 97% of Earth’s water

• Oceans experience 86% of evaporationOceans experience 86% of evaporation

• Oceans receive 78% of planetary precipitationOceans receive 78% of planetary precipitation

• A 1% increase in Atlantic precipitation equals the annual A 1% increase in Atlantic precipitation equals the annual Mississippi runoffMississippi runoff

• A key element of the global water cycleA key element of the global water cycle

The Water Cycle Will Accelerate With The Water Cycle Will Accelerate With Global WarmingGlobal Warming

• A warmer atmosphere A warmer atmosphere will carry more water will carry more water vapor, because of the vapor, because of the exponential increase of exponential increase of vapor pressure with vapor pressure with temperature.temperature.

• An enhanced water An enhanced water cycle will change the cycle will change the distribution of salinity in distribution of salinity in the upper ocean.the upper ocean.

0 5 10 15 20 25 300

5

10

15

20

25

30

35

40

45

Vap

or P

ress

ure

of W

ater

, m

B

Vapor Pressure of Water as Function of Temperature

Temperature, C

0 5 10 15 20 25 300

5

10

15

20

25

30

35

40

45

Vap

or P

ress

ure

of W

ater

, m

B

Vapor Pressure of Water as Function of Temperature

Temperature, C

Sea surface salinity distributions are determined in large part by E-P patterns

Global Salinity and E-P distributions

Source: R.Schmitt,WHOISource: HydroBase2

Increasing Increasing salinities salinities in the in the tropical tropical AtlanticAtlantic

Over the same 40-year period, salinities have been increasing..

…. a shift in the entire Atlantic hydrological cycle?

Ruth Curry et al., 2003

Surface Water

Tropical Salinities Increasing for last 40 yearsTropical Salinities Increasing for last 40 years

Fresher Saltier

Ruth Curry (pers. comm.)

1967-1972 1980-1984 1995-2000

Summer Arctic Sea IceSummer Arctic Sea Ice

1979197920032003 NASA Goddard Space Flight Center

NY Times June 8, 2004

Greenland is melting

Curry and Mauritzen, in press

Largest effects in the upper 1000 m

Freshwater storage and net flux anomalies

Ruth Curry & Cecile Mauritzen, in press

19000 km3

4000 km3

15000 km3

0.066 Sv

10,000 km3

Large Scale Ocean CirculationLarge Scale Ocean Circulation

Fresher Deep Water Flowing South at 3000 mFresher Deep Water Flowing South at 3000 m

Fresher Saltier

Ruth Curry (pers. comm.)

1967-1972 1980-1984 1995-2000

Two Important Ocean Processes Two Important Ocean Processes will be Affectedwill be Affected

Two Important Ocean Processes Two Important Ocean Processes will be Affectedwill be Affected

• Convection and thermohaline circulation – the large scale ocean circulation

• Air-sea coupling – El Nino and the North Atlantic Oscillation

Large-scale Large-scale Ocean Circulation Ocean Circulation Affects the Heat Affects the Heat

TransportTransport

Large Scale Ocean CirculationLarge Scale Ocean Circulation

Conveyor ON

Conveyor OFF

Manabe and Stouffer, 1997

Temperature ResponseTemperature Response

• Strong cooling in North Atlantic

• Warming everywhere else

• No net global change

Greenhouse models predict a Greenhouse models predict a slowdown in the deep water slowdown in the deep water

circulationcirculation

IPCC Report

SummarySummary

• The ocean and atmosphere work together to affect The ocean and atmosphere work together to affect climateclimate

• Surface conditions of the ocean set atmospheric Surface conditions of the ocean set atmospheric circulation – the surface conditions are changingcirculation – the surface conditions are changing

• Deep water produced in the Atlantic is exported to Deep water produced in the Atlantic is exported to the worldthe world

• The circulation system is density driven – warm, salty The circulation system is density driven – warm, salty water becomes cold, dense, salty deep waterwater becomes cold, dense, salty deep water

• The salinity balance appears to be changingThe salinity balance appears to be changing

SummarySummary

• Heat released to the atmosphere by the oceans is an Heat released to the atmosphere by the oceans is an important source of heat to the Atlantic regionimportant source of heat to the Atlantic region

• Several models of future greenhouse climate produce Several models of future greenhouse climate produce a significantly altered Atlantic circulationa significantly altered Atlantic circulation

• Some of the changes predicted by the models may Some of the changes predicted by the models may be occurring in the Atlantic todaybe occurring in the Atlantic today

Air-Sea InteractionsAir-Sea InteractionsAir-Sea InteractionsAir-Sea Interactions

Ocean surface temperatures set atmospheric circulation

El Nino 1997-1998El Nino 1997-1998

January 1997

November 1997

Goddard Space Flight Center - NASAGoddard Space Flight Center - NASA

Goddard Space Flight Center - NASAGoddard Space Flight Center - NASA

High Phase Low Phase

The North Atlantic OscillationThe North Atlantic Oscillation

The North Atlantic OscillationThe North Atlantic Oscillation

High Index Low IndexHigh Index Low IndexFewer hurricanes More hurricanesFewer hurricanes More hurricanes

North Atlantic Oscillation IndexNorth Atlantic Oscillation Index

NAO and Gulf Stream TransportNAO and Gulf Stream Transport

The Gulf Stream South of Cape Cod

The Ocean andClimate Change

Institute

The Ocean andClimate Change

InstituteWoods Hole Oceanographic InstitutionWoods Hole Oceanographic Institution