Ocean and ClimateAn Introduction

Program in Climate Change Summer InstituteFriday Harbor Labs

16-18 September 2008

Dennis L. HartmannAtmospheric Sciences

University of Washington

Ocean and ClimateAn Introduction

• Role in Earth’s Evolution

• Role in Climate Change - Past & Future

• Impact of Ocean Change - e.g. sea level.

• Impact of Human Activities and Climate Change on the Ocean - e.g. acidification.

Basic Properties• The Ocean is Dark - low albedo• The Ocean is Wet - Cools by Evaporation• The Ocean is a fluid with mass/heat capacity

– Can store and release energy quickly (or slowly)– Can move energy around – Can store and release trace chemicals (e.g.CO2)

• The Ocean can freeze, in which case it is a bright solid and energy transfer by phase transition is less important (sublimation).

The Ocean is Dark

Ice-Albedo Feedback

• As the Earth warms, ice melts in high latitudes and altitudes

• This lowers the albedo of Earth and leads to further warming.

• Ice reflects more solar radiation than other surfaces

Ice-Albedo Feedback

• As the Earth warms, ice melts in high latitudes and altitudes

• This lowers the albedo of Earth and leads to further warming.

• Ice reflects more solar radiation than other surfaces

The Ocean is Wet

The Ocean Stores Energy

The Surface Energy Balance

Ocean Heat Capacity

InstantResponse

GCMResponse

Manabe & Stouffer 2007

Heat Capacity/Transport

IPCC AR4

North Atlantic Circulation

Atlantic MOC

IPCC AR4

ENSO

ENSO

El Niño

La Niña

ENSO

El Niño

ENSOStratosphere

El Niño

-

Garfinkel & Hartmann 2007

ENSO State and Variability

IPCC AR4

Tropical SST and Clouds

• Distribution of tropical SST is hypothesized to have strong effect on clouds and the energy balance.

• For example, marine boundary layer clouds have strong leverage on the radiation balance and depend on the strength of the trade winds and SST gradients.

Marine Boundary Layer Clouds

Form above lower SST.

Marine Boundary Layer CloudsMarine Boundary Layer Clouds

0 20 40 60 80%

• Cover a significant fraction of the Earth’s Surface

• Have a large effect on Earth’s Energy Budget

Cloud Forcing of the Energy BalanceCloud Forcing of the Energy Balance

-70 0 +30 Wm-2-30

Ocean a Source/Sink of radiatively active gases and

aerosols.• Carbon uptake/release

– Glacial/Interglacial– Anthropogenic Carbon uptake - 50%

• DMS production - Sulfate Aerosols/CCN• Sea Salt Aerosols

The atmospheric concentration of CO2 and CH4 in 2005 exceeds by far the natural range of the last 650,000 years

CO2

CH4

Ocean Acidification

IPCC AR4

Aragonite Saturation

Ocean Acidity440

570

730

The Ocean Freezes, or not- Sea Ice

• Freezing of seawater an important driver of thermohaline circulation.

• Sea Ice + Snow = insulation• Large albedo increase .• Polar amplification and seasonal

dependence of polar warming - largest polar warming in winter.

Disappearing Sea Ice

Disappearing Sea Ice

Disappearing Sea Ice

Disappearing Sea Ice

Disappearing Sea Ice

Ocean and Clouds