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

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

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

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

Earths CO2 Levels

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.

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

Sea-Level Rise: Observations and Projections

Sea-Level Rise: The Big Unknown Mention accumulation in interior, loss of ice on the margins due to calving and melting/runoff.

Implications for the North Atlantic Ocean Normal Circulation Climate Change Effect

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

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!!

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

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

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)

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

Changing Carbonate Equilibrium in Seawater

Calcium Carbonate (CaCO3) Cycle

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

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