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Ocean and Climate An Introduction Dennis L. Hartmann Atmospheric Sciences University of Washington Program in Climate Change Summer Institute Friday Harbor Labs 16-18 September 2008 Ocean and Climate An 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 • Ice reflects more solar radiation than other surfaces • As the Earth warms, ice melts in high latitudes and altitudes • This lowers the albedo of Earth and leads to further warming. Ice-Albedo Feedback • Ice reflects more solar radiation than other surfaces • As the Earth warms, ice melts in high latitudes and altitudes • This lowers the albedo of Earth and leads to further warming. The Ocean is Wet The Ocean Stores Energy The Surface Energy Balance Ocean Heat Capacity Instant Response GCM Response Manabe & Stouffer 2007 Heat Capacity/Transport IPCC AR4 North Atlantic Circulation Atlantic MOC IPCC AR4 ENSO ENSO La Niña El Niño ENSO El Niño - ENSO Stratosphere 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 Clouds 0 20 40 60 80% Cloud Forcing of the Energy Balance • Cover a significant fraction of the Earth’s Surface • Have a large effect on Earth’s Energy Budget -70 -30 0 +30 Wm-2 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 CO2 CH4 The atmospheric concentration of CO2 and CH4 in 2005 exceeds by far the natural range of the last 650,000 years Ocean Acidification IPCC AR4 Aragonite Saturation Ocean Acidity 440 570 730 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
