Transcript Climate change impact on 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
Global Warming: The Enhanced Greenhouse
Effect
Greenhouse Gases
Outgoing heat
gets trapped
The Importance of Greenhouse Gases
Predict the temperature on Venus?
167°C
470°C
15°C
Extreme Greenhouse
Effect
-63°C
The Greenhouse-Intensive Industrial Revolution
30
25
20
15
Billion tonnes
of Greenhouse
Gas Emissions
10
5
1800
1800
1820
1840
1860
1860
1879
1900
1920
1899
1921
1940
1941
1960
1961
1980
1981
2000
2001
Earths CO2 Levels
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Intergovernmental Panel on Climate Change (2007)
14.5ºC
14.3ºC
Atmospheric
CO2 Levels
(ppm)
Global Mean
14.1ºC Temperature
13.8ºC
13.6ºC
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•
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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
Implications for the North Atlantic
Ocean
Normal Circulation
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Climate Change Effect
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Oceanic Controls on Atmospheric
CO2 :
Atmospheric CO2
Thermodynamic Equilibration
CO2
Water Mass Formation and Subduction
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•
CO2 is very soluble
Ocean circulation stores
and transports vast
quantities
Importance of the Ocean for Atmospheric
CO2
450
440
430
CO2 Without Natural
Sinks
420
410
400
Atmos CO2
(ppm)
390
Oceanic CO2 Absorption
380
370
360
350
Observed CO2
340
330
320
310
1960
1965
1970
1975
1980
1985
1990
1995
2000
2005
Year
•Atmospheric CO2 today would be about 450ppm without the ocean!!
Ocean Circulation with Climate
Change
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Stratification with warming and freshening
Slow-down in overturning circulation
Model Projections of Circulation and
Carbon Cycle
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•
50% slowdown in
overturning circulation
20-30% reduction in
oceanic CO2 uptake
Sarmiento, 1998
Oceanic Biological Pump with Climate
Change
Normal
Climate Change
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•
Phytoplankton
are starved of
nutrients due
to ocean
stratification
~15%
reduction by
the year 2100
Matear (2000)
Unfortunate Consequences of
Oceanic Anthropogenic CO2
Absorption
CO2
Increase
Increase from airsea 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