Ocean Response to Global Warming
William Curry
Woods Hole Oceanographic Institution
Wallace Stegner Center
March 3, 2006
What is the Ocean’s Role in Climate?
• the ocean covers 70% of the earth’s surface
• the ocean stores a thousand times more heat
than the atmosphere
• seawater stores four times more heat per unit
mass than air
• it transports 25 to 50% of the energy received
from the sun
What is the Ocean’s Role in Climate?
• it circulates slowly, on time scales of decades
to centuries
• it is the major source of heat to some regions
like the North Atlantic
• it sets long-term patterns of atmospheric
circulation affecting climate systems like
ENSO, NAO
Equator to Pole Heat Transport
How will the Oceans Change
as the Earth Warms?
• the oceans will warm, sea level will rise
• its salinity balance will be altered
• its ability to absorb CO2 will change
• it will impact atmospheric circulation, storm
tracks, severe storms, and the frequency and
distribution of droughts
The oceans
have been
warming for
the last 50
years
Levitus et al., 2000
The net warming above 3000 m is 0.06o C
The oceans have absorbed about 30 times more
heat than the atmosphere since 1955
Oceans
Atmosphere
18.2 x 1022 J
6.6 x 1021 J
Indistinguishable from the expected response to
rising CO2 – an anthropogenic signal
Levitus et al., 2001
What are the Implications?
The oceans will continue to absorb heat as
the climate system warms
Warming will cause sea water to expand
The effect of ocean heat absorption will be
to delay the warming of the atmosphere
The rate and magnitude of global warming
will be affected by how the ocean circulates
in the future – when and where will it
release the stored heat?
What about Salinity?
• Oceans contain 97% of Earth’s water
• Oceans experience 86% of evaporation
• Oceans receive 78% of planetary precipitation
• A 1% increase in Atlantic precipitation equals the
annual Mississippi runoff
• A key element of the global water cycle
The Water Cycle Will Accelerate With
Global Warming
Vapor Pressure of Water as Function of Temperature
45
40
Vapor Pressure of Water, mB
• A warmer atmosphere
will carry more water
vapor, because of the
exponential increase of
vapor pressure with
temperature.
• An enhanced water
cycle will change the
distribution of salinity in
the upper ocean.
35
30
25
20
15
10
5
0
0
5
10
15
20
Temperature, C
25
30
Global Salinity and E-P distributions
Source: HydroBase2
Source: R.Schmitt,WHOI
Sea surface salinity distributions are determined
in large part by E-P patterns
Increasing
salinities
in the
tropical
Atlantic
Surface Water
Over the same
40-year period,
salinities have
been increasing..
…. a shift in the
entire Atlantic
hydrological
cycle?
Ruth Curry et al., 2003
Tropical Salinities Increasing for last 40 years
1967-1972
1980-1984
Fresher
1995-2000
Saltier
Ruth Curry (pers. comm.)
Summer Arctic Sea Ice
1979
2003
NASA Goddard Space Flight Center
Greenland is
melting
NY Times June 8, 2004
Largest effects in the
upper 1000 m
Curry and Mauritzen, in press
Freshwater storage and net flux anomalies
0.066 Sv
19000 km3
4000 km3
15000
10,000
km3 km
3
Ruth Curry & Cecile Mauritzen, in press
Large Scale Ocean Circulation
Fresher Deep Water Flowing South at 3000 m
1967-1972
1980-1984
Fresher
1995-2000
Saltier
Ruth Curry (pers. comm.)
Two Important Ocean Processes
will be Affected
• Convection and thermohaline circulation – the
large scale ocean circulation
• Air-sea coupling – El Nino and the North
Atlantic Oscillation
Large-scale
Ocean Circulation
Affects the Heat
Transport
Large Scale Ocean Circulation
Conveyor ON
Conveyor OFF
Temperature Response
• Strong cooling in North Atlantic
• Warming everywhere else
• No net global change
Manabe and Stouffer, 1997
Greenhouse models predict a
slowdown in the deep water
circulation
IPCC Report
Summary
• The ocean and atmosphere work together to affect
climate
• Surface conditions of the ocean set atmospheric
circulation – the surface conditions are changing
• Deep water produced in the Atlantic is exported to
the world
• The circulation system is density driven – warm, salty
water becomes cold, dense, salty deep water
• The salinity balance appears to be changing
Summary
• Heat released to the atmosphere by the oceans is an
important source of heat to the Atlantic region
• Several models of future greenhouse climate produce
a significantly altered Atlantic circulation
• Some of the changes predicted by the models may
be occurring in the Atlantic today
Air-Sea Interactions
Ocean surface temperatures set
atmospheric circulation
El Nino 1997-1998
November 1997
January 1997
Goddard Space Flight Center - NASA
Goddard Space Flight Center - NASA
The North Atlantic Oscillation
High Phase
Low Phase
The North Atlantic Oscillation
High Index
Fewer hurricanes
Low Index
More hurricanes
North Atlantic Oscillation Index
NAO and Gulf Stream Transport
The Gulf Stream
South of Cape Cod
The Ocean and
Climate Change
Institute
Woods Hole Oceanographic Institution