Ocean Response to Global Warming/Global Change William Curry Woods Hole Oceanographic Institution Environmental Defense May 12, 2005 Possible changes in ocean circulation and how they may affect regional climate patterns

Ocean Response to Global Warming/Global Change William Curry Woods Hole Oceanographic Institution July 19, 2005 Possible changes in ocean circulation and how they may affect regional climate patterns

What is the Ocean’s Role in Climate? the ocean covers 70% of the earth ’ s surface the ocean covers 70% of the earth ’ s surface the ocean stores a thousand times more heat than the atmosphere the ocean stores a thousand times more heat than the atmosphere seawater stores four times more heat per unit mass than air seawater stores four times more heat per unit mass than air it transports 25 to 50% of the energy received from the sun 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 circulates slowly, on time scales of decades to centuries it is the major source of heat to some regions like the North Atlantic 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 it sets long-term patterns of atmospheric circulation affecting climate systems like ENSO, NAO

How will the Oceans Change as the Earth Warms? the oceans will warm, sea level will rise the oceans will warm, sea level will rise its salinity balance will be altered its salinity balance will be altered its ability to absorb CO 2 will change its ability to absorb CO 2 will change it will impact atmospheric circulation, storm tracks, severe storms, and the frequency and distribution of droughts it will impact atmospheric circulation, storm tracks, severe storms, and the frequency and distribution of droughts

Levitus et al., 2000 The oceans have been warming for the last 50 years

The net warming above 3000 m is 0.06 o C The oceans have absorbed about 30 times more heat than the atmosphere since 1955 Oceans18.2 x J Atmosphere 6.6 x J Indistinguishable from the expected response to rising CO 2 – an anthropogenic signal Levitus et al., 2001

The oceans will continue to absorb heat as the climate system warms Warming will cause sea water to expand The effect of 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 are the Implications?

What about Salinity? Oceans contain 97% of Earth’s water Oceans contain 97% of Earth’s water Oceans experience 86% of evaporation Oceans experience 86% of evaporation Oceans receive 78% of planetary precipitation Oceans receive 78% of planetary precipitation A 1% increase in Atlantic precipitation equals the annual Mississippi runoff A 1% increase in Atlantic precipitation equals the annual Mississippi runoff A key element of the global water cycle A key element of the global water cycle

The Water Cycle Will Accelerate With Global Warming A warmer atmosphere will carry more water vapor, because of the exponential increase of vapor pressure with temperature. 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. An enhanced water cycle will change the distribution of salinity in the upper ocean.

Sea surface salinity distributions are determined in large part by E-P patterns Global Salinity and E-P distributions Source: R.Schmitt,WHOI Source: HydroBase2

Increasing salinities in the tropical Atlantic

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 years FresherSaltier Ruth Curry (pers. comm.)

Summer Arctic Sea Ice 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 km km km Sv 10,000 km 3

Large Scale Ocean Circulation

Fresher Deep Water Flowing South at 3000 m FresherSaltier 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

Manabe and Stouffer, 1997 Temperature Response Strong cooling in North Atlantic Warming everywhere else No net global change

Greenhouse models predict a slowdown in the deep water circulation IPCC Report

Air-Sea Interactions Ocean surface temperatures set atmospheric circulation

El Nino January 1997 November 1997 Goddard Space Flight Center - NASA

High Phase Low Phase The North Atlantic Oscillation

High Index Low Index Fewer hurricanes More hurricanes

North Atlantic Oscillation Index

NAO and Gulf Stream Transport

The Gulf Stream South of Cape Cod

Summary The ocean and atmosphere work together to affect climate The ocean and atmosphere work together to affect climate Surface conditions of the ocean set atmospheric circulation – the surface conditions are changing Surface conditions of the ocean set atmospheric circulation – the surface conditions are changing Deep water produced in the Atlantic is exported to the world 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 circulation system is density driven – warm, salty water becomes cold, dense, salty deep water The salinity balance appears to be changing 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 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 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 Some of the changes predicted by the models may be occurring in the Atlantic today

The Ocean and Climate Change Institute The Ocean and Climate Change Institute Woods Hole Oceanographic Institution