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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