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

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

5. The Greenhouse-Intensive Industrial Revolution30 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)
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
Mention accumulation in interior, loss of ice on the margins due to calving and melting/runoff.

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

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

13. Importance of the Ocean for Atmospheric CO2
Atmos CO2
(ppm)
Year
CO2 Without Natural Sinks
Oceanic CO2 Absorption
Observed CO2
Translating emissions to CO2 concentrations
Illustrates CO2 concentration would be without the natural anthropogenic CO2 sinks
The ocean is the most dominant sink
Atmosphere would be 55ppm higher
However the oceanic absorption is vulnerable to changes in temperature / circulation changes
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
Modelling BGC with climate change
-present oxygen, nutrient and carbon uptake changes
- nutrient supply changes may impact on the ecosystem affect both higher trophic levels and the carbon export to the deep ocean
Need to continue to make observations to provide continue insight into the behavior of both the physical and biological formulations of the model
Need to develop and apply models that incorporate the observations and project the impact of climate change
Need base line observations of the ecosystem. Focus on the lower trophic levels where the links between climate change and marine impacts is more tractable
• 20-30% reduction in oceanic CO2 uptake
Sarmiento, 1998

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

17. Unfortunate Consequences of Oceanic Anthropogenic CO2 Absorption
Increase
Increase from air-sea exchange
CO2 + H2O  HCO H+  CO H+
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