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Climate Change and the Oceans

Climate Change and the Oceans. Ben McNeil Climate Change Research Centre The University of New South Wales. The Natural Greenhouse Effect. Incoming Shortwave Solar Radiation. Outgoing Longwave Radiation. Greenhouse Gases. Global Warming: The Enhanced Greenhouse Effect.

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Climate Change and the Oceans

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  1. Climate Change and the Oceans Ben McNeil Climate Change Research Centre The University of New South Wales

  2. The Natural Greenhouse Effect Incoming Shortwave Solar Radiation Outgoing Longwave Radiation

  3. Greenhouse Gases Global Warming: The Enhanced Greenhouse Effect Outgoing heat gets trapped

  4. Extreme Greenhouse Effect The Importance of Greenhouse Gases Predict the temperature on Venus? 470°C 15°C -63°C 167°C

  5. The Greenhouse-Intensive Industrial Revolution 30 25 20 15 Billion tonnes of Greenhouse Gas Emissions 10 5 1800 1860 1900 1920 1940 1960 1980 2000

  6. Earths CO2 Levels

  7. Intergovernmental Panel on Climate Change (2007) 14.5ºC 14.3ºC Atmospheric CO2 Levels (ppm) Global Mean Temperature 14.1ºC 13.8ºC 13.6ºC • The planet has warmed about 0.75°C in the last century • Twelve of the last 13 years are the warmest years since 1850 • “Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global mean sea level”,IPCC 4th Assessment Report.

  8. Dramatic Warming Evidence from the Arctic Since IPCC Analysis 2007 Stroeve et al. GRL 2007

  9. Sea-Level Rise: Observations and Projections

  10. Sea-Level Rise: The Big Unknown

  11. Implications for the North Atlantic Ocean Normal Circulation Climate Change Effect

  12. Oceanic Controls on Atmospheric CO2 : • CO2 is very soluble • Ocean circulation stores and transports vast quantities Atmospheric CO2 Thermodynamic Equilibration CO2 Water Mass Formation and Subduction

  13. Importance of the Ocean for Atmospheric CO2 CO2 Without Natural Sinks Atmos CO2 (ppm) Oceanic CO2 Absorption Year Observed CO2 • Atmospheric CO2 today would be about 450ppm without the ocean!!

  14. Ocean Circulation with Climate Change • Stratification with warming and freshening • Slow-down in overturning circulation

  15. Model Projections of Circulation and Carbon Cycle • 50% slowdown in overturning circulation • 20-30% reduction in oceanic CO2 uptake Sarmiento, 1998

  16. Oceanic Biological Pump with Climate Change • Phytoplankton are starved of nutrients due to ocean stratification • ~15% reduction by the year 2100 Normal Climate Change Matear (2000)

  17. Unfortunate Consequences of Oceanic Anthropogenic CO2 Absorption CO2 Increase Increase from air-sea exchange CO2 + H2O  HCO3- + H+ CO32- + 2H+ Decrease pH = -log[H+] More CO2 Uptake = More Acidic = Less CO32-

  18. Changing Carbonate Equilibrium in Seawater

  19. Calcium Carbonate (CaCO3) Cycle

  20. Direct Impact of Elevated CO2 on Phytoplankton and Coral Reefs Low CO2 • Elevated CO2levels reduces the calcification rate of phytoplankton and corals High CO2 Riebesell et al, [2000] (Coccolithophores) 1um

  21. Oceans and Climate Change: Summary • Ocean is and will continue to absorb massive amounts of CO2 and the warmth humans are imposing on earth • Ocean circulation is likely to slowdown in a warmer world leading to • Big changes in regional climate • Lower CO2 uptake and therefore more work for us to do • Lower biological productivity and consequences to fishing industry • Sea-level rise and its problems • Chemical alterations to calcifying organisms due to ocean acidification

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