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OCN 623 – Chemical Oceanography
The “unnatural” carbon dioxide cycle and oceanic processes over the last few hundred years
In the 19th century, scientists realized that gases in the atmosphere cause a "greenhouse effect" which affects the planet's temperature. These scientists were interested chiefly in the possibility that a lower level of carbon dioxide gas might explain the ice ages of the distant past.
At the turn of the century, Svante Arrhenius calculated that emissions from human industry might someday bring a global warming. Other scientists dismissed his idea as faulty.
In 1938, G.S. Callendar argued that the level of carbon dioxide was climbing and raising global temperature, but most scientists found his arguments implausible.
In the early 1960s, C.D. Keeling measured the level of carbon dioxide in the atmosphere: it was rising fast. Researchers began to take an interest, struggling to understand how the level of carbon dioxide had changed in the past, and how the level was influenced by chemical and biological forces...
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Absorption of incident and emitted radiation
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Ocean Carbon Chemistry Review CO2(gas)
CO2 + H2O H2CO3
H3CO2 H+ + HCO3
-
HCO3- H+
+ CO32-
Carbonic acid
Bicarbonate
Carbonate
CO2 + CO32- 2 HCO3
-
TCO2
Ocean Carbon Chemistry Review CO2(gas)
CO2 + H2O H2CO3
H3CO2 H+ + HCO3
-
HCO3- H+
+ CO32-
Carbonic acid
Bicarbonate
Carbonate
CO2 + CO32- 2 HCO3
-
280 µatm 560 µatm
8 µmol kg-1
1617 µmol kg-1
268 µmol kg-1
15 µmol kg-1
1850 µmol kg-1
176 µmol kg-1
1893 µmol kg-1 2040 µmol kg-1
100% ΔpCO2 8% ΔTCO2
TCO2
Taken from Feely et al. (2001)
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Factors influencing CO2 flux estimates
Wind
k ΔpCO2
Air-Sea CO2Flux
SST
Transport
Biology Wind Waves
Bubbles Surface Film
Near Surface Turbulence
Bock et al. (1999)
Annual cycle of plant growth and death moves CO2 between atmosphere and biosphere and back again
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Carbon dioxide MRT 5 yrs, seasonal variation, greatest in N. hemisphere
Recent atmospheric carbon dioxide levels Atmospheric CO2 levels have risen from ~315 ppmv in 1958 to 392 ppmv in 2011 (~25%)
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Air bubbles trapped in ice indicate pre-industrial CO2 levels
Put together, the anthropogenic effect is unmistakable 278 ppmv to 392 ppmv (2011), a 41% increase
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Rate of increase of atmospheric CO2 is not constant
Varies with: Economic activity Natural variations: El Nino Droughts, fires Volcanic activity
Carbon reservoirs
Largest reservoirs are carbonate sediments and organic carbon in soils Are not believed to have changed significantly over last 300 years Oceans have 70 times as much CO2 in them as atmosphere Fossil fuels and sedimentary organic carbon contain 13 times as much CO2 as current atmosphere Planetary biomass constant over last 200 - 300 years?
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Natural and anthropogenic carbon dioxide cycle Global fossil fuel combustion adds 7 billion tons C/yr Only 50 % remains in atmosphere
Other emissions
Cl + O3 ---> ClO + O2 ClO + O3 ---> 2O2 + Cl
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Emissions from Fossil Fuel + Cement
Data Source: G. Marland, T.A. Boden, R.J. Andres, and J. Gregg at CDIAC
1990 - 1999: 0.9% y-1 2000 - 2007: 3.5% y-1
1850 1870 1890 1910 1930 1950 1970 1990 2010
2007 Fossil Fuel: 8.5 Pg C
Fossil Fuel Emission: Actual vs. IPCC Scenarios
Raupach et al 2007, PNAS (updated)
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Regional Shift in Emissions Share
Perce
ntage
of G
lobal
Annu
al Em
ission
s
Kyoto Reference Year
FCCC
Kyoto Protocol Adopted
Kyoto Protocol Enter into Force
Current
J. Gregg and G. Marland, 2008, personal communication
62% 57%
49.7%
47% 38%
43% 50.3%
53%
Raupach et al. 2007, PNAS
Cumulative Emissions [1751-2004]
Flux in 2004
Flux Growth in 2004
Population in 2004
0%
20%
40%
60%
80%
100% D3-Least Developed Countries
India
D2-Developing Countries
China FSU D1-Developed Countries Japan EU
USA
Regional Share of Fossil Fuel Emissions
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Carbon Intensity of the Global Economy
Raupach et al. 2007, PNAS; Canadell et al. 2007, PNAS
Carb
on in
tensit
y (K
gC/U
S$)
Kg Carbon Emitted to Produce 1 $ of Wealth
1960 1970 1980 1990 2000 2006
Photo
: CSI
RO
Raupach et al 2007, PNAS
0.5 0.6 0.7 0.8 0.9
1 1.1 1.2 1.3 1.4 1.5
1980 0.5 0.6 0.7 0.8 0.9
1 1.1 1.2 1.3 1.4 1.5
1980
World
0.5 0.6 0.7 0.8 0.9
1 1.1 1.2 1.3 1.4 1.5
1980 1985 1990 1995 2000 2005
F (emissions) P (population) g = G/P h = F/G
Facto
r (re
lative
to 19
90)
Emissions Population Wealth = per capita GDP Carbon intensity of GDP
Drivers of Anthropogenic Emissions
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Regional Emission Pathways
C emissions
Population
C Intensity
Developed Countries (-)
Developing Countries Least Developed Countries
Wealth per capita
Raupach et al 2007, PNAS
Canadell et al. 2007, PNAS; FAO-Global Resources Assessment 2005
Tropical Americas 0.6 Pg C y-1
Tropical Asia 0.6 Pg C y-1
Tropical Africa 0.3 Pg C y-1
2000-2007
Tropical deforestation 13 Million hectares each year
Carbon Emissions from Land Use Change
1.5 Pg C y-1
Born
eo, C
ourte
sy: V
iktor
Boe
hm
[2007-Total Anthropogenic Emissions:8.5+1.5 = 10 Pg]
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R.A. Houghton, unpublished
Carbon Emissions from Tropical Deforestation Pg
C y
r-1
0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80
1850
1860
1870
1880
1890
1900
1910
1920
1930
1940
1950
1960
1970
1980
1990
2000
Africa Latin America S. & SE Asia
Historical Emissions from Land Use Change
SUM
2000-2007
1.5 Pg C y-1 (16% total emissions)
Canadell, Raupach, Houghton, 2008, Biogeosciences, submitted
Regional Share of Emissions from Land Use Change
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13C is affected by fossil fuel combustion
Missing CO2
Oceans Dissolution into surface water Limited by slow mixing of surface and deep waters
Land Regrowth of temperate forests (logged out in the past) Fertilisation of forests by CO2 and N, P
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Fate of Anthropogenic CO2 Emissions (2000-2007)
Canadell et al. 2007, PNAS (updated)
1.5 Pg C y-1
+ 7.5 Pg C y-1
Atmosphere 46%
4.2 Pg y-1
Land 29%
2.6 Pg y-1
Oceans 26%
2.3 Pg y-1
Climate Change at 55% Discount
Natural CO2 sinks absorb 55% of all anthropogenic carbon emissions slowing down climate change significantly.
They are in effect a huge subsidy to the global economy worth half a trillion US$ annually if an equivalent sink had to be created using other climate mitigation options (based on the cost of carbon in the EU-ETS).
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1. The rate of CO2 emissions.
2. The rate of CO2 uptake and ultimately the total amount of C that can be stored by land and oceans:
– Land: CO2 fertilization effect, soil respiration, N deposition fertilization, forest regrowth, woody encroachment, …
– Oceans: CO2 solubility (temperature, salinity),, ocean currents, stratification, winds, biological activity, acidification, …
Factors that Influence the Airborne Fraction
Springer; Gruber et al. 2004, Island Press
% C
O 2 Emi
ssion
s in
Atmo
sphe
re
1960 2000 1980 1970 1990
Canadell et al. 2007, PNAS
2006
Decline in the Efficiency of CO2 Natural Sinks
Fraction of all anthropogenic emissions that stay in the atmosphere
Emissions 1 tCO2
400Kg stay
Emissions 1 tCO2
450Kg stay
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Efficiency of Natural Sinks
Land Fraction
Ocean Fraction
Canadell et al. 2007, PNAS
• Part of the decline is attributed to up to a 30% decrease in the efficiency of the Southern Ocean sink over the last 20 years.
• This sink removes annually 0.7 Pg of anthropogenic carbon.
• The decline is attributed to the strengthening of the winds around Antarctica which enhances ventilation of natural carbon-rich deep waters.
• The strengthening of the winds is attributed to global warming and the ozone hole.
Causes of the Decline in the Efficiency of the Ocean Sink
Le Quéré et al. 2007, Science
Cred
it: N.
Metzl
, Aug
ust 2
000,
ocea
nogr
aphic
cruis
e OIS
O-5
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Human Perturbation of the Global Carbon Budget
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http://lgmacweb.env.uea.ac.uk/lequere/co2/carbon_budget.htm
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Canadell et al. 2007, PNAS (updated to 2007)
Human Perturbation of the Global Carbon Budget
Fossil fuel intensity
CO2 budget (1959-2006)
sources
fate of emissions
65% - Increased activity of the global economy
Canadell et al. 2007, PNAS
17% - Deterioration of the carbon intensity of the global economy
18% - Decreased efficiency of natural sinks
2000 - 2007: 2.0 ppm y-1
1970 – 1979: 1.3 ppm y-1
1980 – 1989: 1.6 ppm y1
1990 – 1999: 1.5 ppm y-1
Drivers of Accelerating Atmospheric CO2
To: • Economic growth • Carbon intensity • Efficiency of natural sinks
(calculations based on the period 2000-2006)
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• Anthropogenic CO2 emissions are growing x4 faster since 2000 than during the previous decade, and above the worst case emission scenario of the Intergovernmental Panel on Climate Change (IPCC).
• The carbon intensity of the world’s economy is improving slower than previous decades.
• Less Developed Countries are now emitting more carbon than Developed Countries.
Conclusions (i)
• The efficiency of natural sinks has decreased by 5% over the last 50 years (and will continue to do so in the future), implying that the longer it takes to begin reducing emissions significantly, the larger the cuts needed to stabilize atmospheric CO2.
• All these changes have led to an acceleration of atmospheric CO2 growth 33% faster since 2000 than in the previous two decades, implying a stronger climate forcing and sooner than expected.
Conclusions (ii)
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Consequences of the enhanced Greenhouse effect
Temperature and precipitation changes
Response of the atmosphere-ocean system: deep water circulation, sea level, calcification rates
Response of the atmosphere-land system: Photosynthesis and respiration/decay rates: shifts in biomes/habitats
Knowledge stems from models, historical and proxy records, observations of modern climate system