met 112 global climate change - lecture 8

1 MET 112 Global Climate MET 112 Global Climate ChangeChange

MET 112 Global Climate Change - Lecture 8

The Carbon CycleDr. Craig Clements

San José State University

Outline Earth system perspective Carbon: what’s the big deal? Carbon: exchanges Long term carbon exchanges


Goals

We want to understand the difference between short term and long term carbon cycle

We want to understand the main components of the long term carbon cycle


An Earth System Perspective

Earth composed of:– Atmosphere– Hydrosphere– Cryosphere– Land Surfaces– Biosphere

These ‘Machines’ run the Earth


The Earth’s history can be characterized by different geologic events or eras.


Hydrosphere

Component comprising all liquid water– Surface and subterranean (ground water)

Fresh/Salt water Thus…lakes, streams, rivers, oceans…

Oceans:– Oceans currently cover ~ 70% of earth– Average depth of oceans: 3.5 km– Oceans store large amount of energy– Oceans dissolve carbon dioxide (more later)– Circulation driven by wind systems– Sea Level has varied significantly over Earth’s history– Slow to heat up and cool down


Cryosphere

Component comprising all ice– Glaciers– Ice sheets:

Antarctica, Greenland, Patagonia– Sea Ice– Snow Fields

Climate:– Typically high albedo surface– Positive feedback possibility Store large amounts of

water; sea level variations.


Land Surfaces

Continents Soils surfaces and vegetation Volcanoes

Climate:– Location of continents controls

ocean/atmosphere circulations– Volcanoes return CO2 to atmosphere– Volcanic aerosols affect climate


Biosphere

All living organisms; (Biota) Biota- "The living plants and animals of a

region.“ or "The sum total of all organisms alive today”– Marine– Terrestrial

Climate: Photosynthetic process store significant amount

of carbon (from CO2)


Interactions Between Components of Earth System

Hydrologic Cycle (Hydrosphere, Surface,and Atmosphere)– Evaporation from surface puts water vapor into

atmosphere– Precipitation transfers water from atmosphere to

surface Cryosphere-Hydrosphere

– When glaciers and ice sheets shrink, sea level rises– When glaciers and ice sheets grow, sea level falls

When ice sheets melt and thus sea levels rise, which components of the earth system are interacting? 1. Atmosphere-Cryosphere2. Atmosphere-Hydropshere3. Hydrosphere-Cryosphere4. Atmosphere-Biosphere5. Hydrosphere-Biosphere

When water from lakes and the ocean evaporates, which components of the earth system are interacting?

1. Land Surface – atmosphere2. Hydrosphere-atmosphere3. Hydrosphere-land surface4. Crysophere-Atmosphere5. Biosphere-Atmosphere

The Earth’s history can be characterized by different geologic events or eras.


Interactions

Components of the Earth System are linked by various exchanges including

Energy Water (previous example) Carbon

In this lecture, we are going to focus on the exchange of Carbon within the Earth System


Carbon: what is it? Carbon (C), the fourth most abundant element

in the Universe, Building block of life.

– from fossil fuels and DNA – Carbon cycles through the land (bioshpere),

ocean, atmosphere, and the Earth’s interior Carbon found

– in all living things – in the atmosphere – in the layers of limestone sediment on the

ocean floor– in fossil fuels like coal


Carbon: where is it?

Exists:– Atmosphere:

–CO2 and CH4 (to lesser extent)– Living biota (plants/animals)

–Carbon– Soils and Detritus

–Carbon–Methane

– Oceans–Dissolved CO2

–Most carbon in the deep ocean


Carbon conservation

Initial carbon present during Earth’s formation

Carbon doesn’t increase or decrease globally

Carbon is exchanged between different components of Earth System.


The Carbon Cycle

The complex series of reactions by which carbon passes through the Earth's

– Atmosphere – Land (biosphere and Earth’s crust)– Oceans

Carbon is exchanged in the earth system at all time scales

- Long term cycle (hundreds to millions of years)- Short term cycle (from seconds to a few years)


The carbon cycle has different speeds

Short Term Carbon Cycle

Long Term Carbon Cycle



One example of the short term carbon cycle involves plants Photosynthesis: is the conversion of carbon dioxide and

water into a sugar called glucose (carbohydrate) using sunlight energy. Oxygen is produced as a waste product.

Plants require Sunlight, water and carbon, (from CO2 in atmosphere or

ocean) to produce carbohydrates (food) to grow. When plants decay, carbon is mostly returned to the

atmosphere (respiration)

Global CO2



One example of the short term carbon cycle involves plants Photosynthesis: is the conversion of carbon dioxide and

water into a sugar called glucose (carbohydrate) using sunlight energy. Oxygen is produced as a waste product.

Plants require Sunlight, water and carbon, (from CO2 in atmosphere or

ocean) to produce carbohydrates (food) to grow. When plants decay, carbon is mostly returned to the

atmosphere (respiration)

During spring: (more photosynthesis) atmospheric CO2 levels go down (slightly)

During fall: (more respiration) atmospheric CO2 levels go up (slightly)


Carbon exchange (short term)

Other examples of short term carbon exchanges include:

Soils and Detritus: - organic matter decays and releases carbon

Surface Oceans– absorb CO2 via photosynthesis– also release CO2


Short Term Carbon Exchanges



Carbon is slowly and continuously being transported around our earth system.– Between atmosphere/ocean/biosphere – And the Earth’s crust (rocks like limestone)

The main components to the long term carbon cycle:



Carbon is slowly and continuously being transported around our earth system.– Between atmosphere/ocean/biosphere – And the Earth’s crust (rocks like limestone)

The main components to the long term carbon cycle:1. Chemical weathering (or called: “silicate to

carbonate conversion process”)2. Volcanism/Subduction3. Organic carbon burial4. Oxidation of organic carbon


The Long-Term Carbon Cycle (Diagram)

Atmosphere (CO2)

Ocean (Dissolved CO2)

Biosphere (Organic Carbon)

Carbonates Buried Organic Carbon

Subduction/Volcanism

Silicate-to-Carbonate Conversion

Organic Carbon Burial

Oxidation of Buried Organic Carbon


Where is most of the carbon today?

Most Carbon is ‘locked’ away in the earth’s crust (i.e. rocks) as – Carbonates (containing carbon)

Limestone is mainly made of calcium carbonate (CaCO3)

Carbonates are formed by a complex geochemical process called:– Silicate-to-Carbonate Conversion (long term carbon

cycle)


Silicate to carbonate conversion – chemical

weathering

One component of the long term carbon cycle


Granite (A Silicate Rock)


Limestone (A Carbonate Rock)



1. Chemical Weathering Phase• CO2 + rainwater carbonic acid• Carbonic acid dissolves silicate rock

2. Transport Phase• Solution products transported to ocean by

rivers3. Formation Phase

• In oceans, calcium carbonate precipitates out of solution and settles to the bottom



Rain1. CO2 Dissolves in Rainwater2. Acid

Dissolves Silicates (carbonic acid)

3. Dissolved Material Transported to Oceans

4. CaCO3 Forms in Ocean and Settles to the Bottom

Calcium carbonate

Land


Changes in chemical weathering

The process is temperature dependant: – rate of evaporation of water is temperature

dependant– so, increasing temperature increases weathering

(more water vapor, more clouds, more rain)

Thus as CO2 in the atmosphere rises, the planet warms. Evaporation increases, thus the flow of carbon into the rock cycle increases removing CO2 from the atmosphere and lowering the planet’s temperature– Negative feedback


Earth vs. Venus

The amount of carbon in carbonate minerals (e.g., limestone) is approximately– the same as the amount of carbon in Venus’

atmosphere

On Earth, most of the CO2 produced is – now “locked up” in the carbonates

On Venus, the silicate-to-carbonate conversion process apparently never took place

Subjuction/Volcanism

Another Component of the Long-Term Carbon Cycle


Subduction

Definition: The process of the ocean plate descending beneath the continental plate.

During this processes, extreme heat and pressure convert carbonate rocks eventually into CO2


Volcanic Eruption

Mt. Pinatubo (June 15, 1991)

Eruption injected (Mt – megatons)

17 Mt SO2, 42 Mt CO2,

3 Mt Cl, 491 Mt H2O

Can inject large amounts of CO2 into the atmosphere

Organic Carbon Burial/Oxidation of Buried Carbon

Another Component of the Long-Term Carbon Cycle


Buried organic carbon (1)

Living plants remove CO2 from the atmosphere by the process of – photosynthesis

When dead plants decay, the CO2 is put back into the atmosphere – fairly quickly when the carbon in the plants is

oxidized However, some carbon escapes oxidation

when it is covered up by sediments


Organic Carbon Burial Process

CO2 Removed by Photo-Synthesis

CO2 Put Into Atmosphere by Decay

CC

O2

Some Carbon escapes oxidation

CResult: Carbon into land



Eventually, buried organic carbon may be exposed by erosion

The carbon is then oxidized to CO2



Atmosphere

Buried Carbon (e.g., coal)



Atmosphere

Buried Carbon (e.g., coal)

Erosion



Atmosphere

Buried Carbon

O2

CO2

C

Result: Carbon into atmosphere (CO2)


The (Almost) Complete Long-Term Carbon Cycle

Inorganic Component– Silicate-to-Carbonate Conversion – Subduction/Volcanism

Organic Component– Organic Carbon Burial– Oxidation of Buried Organic Carbon


The Long-Term Carbon Cycle (Diagram)

Atmosphere (CO2)

Ocean (Dissolved CO2)

Biosphere (Organic Carbon)

Carbonates Buried Organic Carbon

Subduction/Volcanism


Organic Carbon Burial



Review of Long Term Carbon Cycle


If volcanism was to increase over a period of thousands of years, how would this affect atmospheric CO2 levels?

Atmospheric CO2 levels would

Increas

e

Decrea

se

Stay th

e sam

e

Are not re

lated

to vo

l...

92%

0%0%8%

1. Increase2. Decrease3. Stay the same4. Are not related to

volcanism


If the silicate to carbonate conversion process was to increase over a period of millions of years, how would this affect volcanism?

Volcanism would

Increas

e

Decrea

se

Stay th

e sam

e

Not be a

ffecte

d by t

he ...

43%35%

14%8%

1. Increase2. Decrease3. Stay the same4. Not be affected by

the silicate to carbonate conversion process


If the oxidation of organic carbon was to increase, how would global temperatures respond?

Global temperatures

Would incr

ease

Would decrea

se

Would stay

the s

ame

Are not a

ffecte

d by th...

86%

8%4%2%

1. Would increase2. Would decrease3. Would stay the same4. Are not affected by

the oxidation of organic carbon


If there was a decline in the silicate to carbonate conversion process, how would global temperatures respond?

Global temperatures

Would incr

ease

Would decrea

se

Would stay

the s

ame

Are not a

ffecte

d by the..

.

42%

15%8%

35%1. Would increase2. Would decrease3. Would stay the same4. Are not affected by

the silicate to carbonate conversion process


Activity (groups of two)Imagine that the global temperature were to

increase significantly for some reason.

1. How would the silicate-to-carbonate conversion process change during this warming period. Explain.

2. How would this affect atmospheric CO2 levels and as a result, global temperature?

3. What type of feedback process would this be and why (positive or negative)?


The silicate to carbonate conversion processes would

Increas

e

Decrea

se

Remain

unchan

ged

Impo

ssible

to tell

82%

0%0%

18%

1. Increase2. Decrease3. Remain unchanged4. Impossible to tell

Imagine that the global temperature were to increase significantly for some reason.


How would atmospheric CO2 levels change?

Increas

e

Decrea

se

Stay th

e sam

e

Impo

ssible

to tell

30%

0%6%

64%1. Increase2. Decrease3. Stay the same4. Impossible to tell


How would this affect global temps?

Increas

e

Decrea

se

Stay th

e sam

e

Impo

ssible

to tell

2% 0%0%

98%1. Increase2. Decrease3. Stay the same4. Impossible to tell


What type of feedback process would this be

Positiv

e

Negati

ve

Neither

Both

12%2%0%

86%1. Positive2. Negative3. Neither4. Both


End


Effect of Imbalances

Atmosphere-Ocean-Biosphere

Earth’s Crust

What would happen?

Imbalances in the long-term carbon cycle can cause slow, but sizeable changes in atmospheric

CO2



Earth’s Crust

Consider the long term carbon cycle as seen below Suppose the Atmosphere-Ocean-Biosphere has 40,000 Gt* of

carbon and the earth’s crust has 40,000,000 Gt of carbon

*1 Gt = 1015 grams


Atmosphere-Ocean-Biosphere40,000 Gt

Earth’s Crust40,000,000 Gt

Suppose that an imbalance developed in which the amount leaving the Atm/Ocean/Biosphere was to decrease by 1%.

If the arrows represent flux (carbon moving), and flux from the Earth’s crust to the atm/ocean/bio (labeled B) is 0.03Gt/year, what would the flux be for arrow A?

*1 Gt = 1015 grams

A B 0.0300 Gt./yr


Arrow A would be

0 of 5 0.03

Gt/y

r

0.3 G

t/yr

0.02

97 G

t/yr

0.03

03 G

t/yr

0% 0%0%0%

1. 0.03 Gt/yr2. 0.3 Gt/yr3. 0.0297 Gt/yr4. 0.0303 Gt/yr



Earth’s Crust 40,000,000 Gt

For such an imbalance as shown below, what is the net carbon flux and in what direction?

*1 Gt = 1015 grams

A B 0.0300 Gt./yr

0.0297 Gt./yr


For such an imbalance as shown below, what is the net carbon flux and in what direction?

0 of 5 0.03

3 - up

0.033

down

0.000

3 up

0.000

3 down

0% 0%0%0%

1. 0.033 - up2. 0.033 down3. 0.0003 up4. 0.0003 down



Earth’s Crust40,000,000 Gt

Based on the below Carbon Flux information, how many years will it take for the carbon in the atm/ocean/bio to double?

*1 Gt = 1015 grams

A B 0.0300 Gt./yr

0.0297 Gt./yr

Net Carbon Flux

0.0003 Gt./yr


How many years will it take for the carbon in the atm/ocean/bio to double?

0 of 50.0

3 yea

rs

12 ye

ars

100,0

00 ye

ars

133 m

illion ye

ars

0% 0%0%0%

1. 0.03 years2. 12 years3. 100,000 years4. 133 million years



Earth’s Crust

Based on the below Carbon Flux information, how many years will it take for the carbon in the atm/ocean/bio to double?

*1 Gt = 1015 grams

A B 0.0300 Gt./yr

0.0297 Gt./yr

Net Carbon Flux

0.0003 Gt./yr

Answer: 40, 000/.0003 years = 133 million years


Long-Term CO2 Changes

Source: Berner, R. A., The rise of plants and their effect on weathering and atmospheric CO2. Science, 276, 544-546.


Time Scale (Continued)

The preceding operation would remove 40, 000 Gt. of carbon from the crust;

This is only 0.1% of the carbon in the crust Thus, it is perfectly plausible that such an

imbalance could be sustained


Long-Term Carbon Cycle (Quantitative Assessment)


Earth’s Crust

Carbon Content: 40, 000 Gt*.

Carbon Content: 40, 000, 000 Gt.

Carbon Flux: 0.03 Gt/yr

*1 Gt = 1015 grams

Carbon Flux: 0.03 Gt/yr

met 112 global climate change - lecture 8

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