State of knowledge on the vulnerability of the oceanic CO2 sink

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State of knowledge on the vulnerability of the
oceanic CO2 sink Corinne Le Quéré British
Antarctic Survey and University of East Anglia
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• Outline
• observed changes
• the global carbon cycle
• ocean physics
• ocean biogeochemistry
• outlook at the future

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• Outline
• observed changes
• the global carbon cycle
• ocean physics
• ocean biogeochemistry
• outlook at the future

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7.9 GtC/y in 2005 (28 from 1990)
sources
CO2 flux (GtC/y)
sinks
time (y)
2006 CO2 budget will be published by the Global
Carbon Project in July http//www.globalcarbonproj
ect.org/budget.htm
Canadell et al., subm. PNAS
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fossil fuel intensity (kgC/US)
annual trend GtC/y 2000-2005 0.27
1957-2000 0.11
sources
CO2 flux (GtC/y)
sinks
time (y)
9 of the increase is atmospheric CO2 in
2000-2005 compared to 1970-2000 is caused by the
reversal of the trend in fossil fuel intensity
Raupach et al., in press. PNAS
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sources
CO2 flux (GtC/y)
sinks
time (y)
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sources
CO2 flux (GtC/y)
sinks
time (y)
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Fraction of the CO2 emitted by human activities
which remains in the atmosphere
airborne fraction atm fossil fuel cement
land use emissions
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Fraction of the CO2 emitted by human activities
which remains in the atmosphere
10 increase in cumulative airborne fraction
between 1965 and 2005
8 of the increase in atmospheric CO2 in
2000-2005 compared to 1970-2000 is cased by the
increase in airborne fraction
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relative change in observations
cumulative airborne fraction
time (y)
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relative change in C4MIP models
cumulative airborne fraction
time (y)
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sources
CO2 flux (GtC/y)
sinks
time (y)
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WGI can we identify where air-sea CO2 fluxes
have changed?
sources
CO2 flux (GtC/y)
sinks
time (y)
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• Outline
• observed changes
• the global carbon cycle
• ocean physics (from upcoming IPCC)
• ocean biogeochemistry
• outlook at the future

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Change in oceanic heat content
0.10oC
0-700 m
large rate during 1993-2003
1955
2005
based on Levitus, Ishii and Willis et al. in
Willebrand, Bindoff et al. in press IPCC-2007
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distribution of temperature profiles
1955-1959
1994-1998
based on Levitus et al. 2005 in Willebrand,
Bindoff et al. in press IPCC-2007
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linear trend of change in heat content
(1955-2003, contour 0.25 W/m2)
based on Levitus et al. 2005 in Willebrand,
Bindoff et al. in press IPCC-2007
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linear trend of change in salinity (1955-1998)
freshening
more saline
based on Levitus et al. 2005 in Willebrand,
Bindoff et al. in press IPCC-2007
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Change in salinity
Atlantic (1985-1999 minus 1955-1969)
Pacific (1991-1992 minus 1968/-7 years)
50S latitude 50N
based on Curry et al. 2003 in Willebrand, Bindoff
et al. in press IPCC-2007
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• No evidence for trends in ocean circulation
• no coherent evidence for a trend in the strength
  of the Meridional Overturning Circulation
• no evidence for a systematic trend in volume
  transport of the Antarctic Circumpolar Current
• growing evidence for changes in Antarctic Bottom
  Waters
• evidence for regional variability associated
  with NAO, PDO and SAM

Willebrand, Bindoff et al. in press IPCC-2007
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Change in oceanic global sea level

• Rates of sea level rise (mm yr-1)
• 1961-2003 1.8 0.5
• 1993-2003 3.1 0.7

WGI can we identify where air-sea CO2 fluxes are
most susceptible to changes in the future
(vulnerables)?
Willebrand, Bindoff et al. in press IPCC-2007
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• Outline
• observed changes
• the global carbon cycle
• ocean physics
• ocean biogeochemistry (from upcoming IPCC)
• outlook at the future

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anthropogenic carbon inventory
1750-1994
based on Sabine et al., 2004 in Willebrand,
Bindoff et al. in press IPCC-2007
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Change in surface ocean pCO2 and pH
1982 2005
1982 2005
the increase in anthropogenic carbon caused a
decrease in surface pH by 0.1 since 1750
(indirect method), or a decrease of 0.02 pH units
per decade since 1980 (direct method)
based on Bates, Dore, Gonzàles-Dàvila et al. in
Willebrand, Bindoff et al. in press IPCC-2007
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Change in ocean CO2 uptake?
It is more likely than not that the fraction of
all the emitted CO2 that was taken up by the
oceans has decreased, from 427 during 1750-1994
to 377 during 1980-2005. This would be
consistent with the expected rate at which the
oceans can absorb carbon, but the uncertainty in
this estimate does not allow firm conclusions.
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Change in oxygen concentration
the decrease in mode water O2 concentration is
everywhere consistent with reduced ventilation.
However the time period (1990-1970) is too short
to conclude on the presence of a trend
based on Emerson, Deutsch et al in Willebrand,
Bindoff et al. in press IPCC-2007
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The patterns of observed changes are broadly
consistent with the observed ocean surface
changes and the known characteristics of the
large-scale ocean circulation
Willebrand, Bindoff et al. in press IPCC-2007
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synthesis figure
WGI can we identify the underlying processes?
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• Outline
• observed changes
• the global carbon cycle
• ocean physics
• ocean biogeochemistry
• outlook at the future

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CO2 emissions (GtC/y)
1990
2010
2000
time (y)
Raupach et al. in press PNAS
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Changes have already been observed in the
global carbon
cycle and physical environment WGI task Can we
identify from field observations and model
outputs the most likely regions where air-sea
CO2 fluxes have changes in the recent past
and are most susceptible to changes in the
future (vulnerables)? Can we identify the
underlying processes? Can we assess the content
and quality of the models used to quantify the
observed and projected changes?