Global Carbon CyclingWhere does it all go?

Main Concepts

Pre-anthropogenic CO2 fluxes in and out

Current CO2 fluxesWhat are C reservoirs?Carbon Residence time?Timescales of carbon removal from the

atmosphere.

IPCC AR5 (2013)

Carbon: Ins and Outs

Atmospheric CO2

What are the major sources of C emissions? How unique are modern CO2 levels? Where does it all go?How long will it stick around?

Fossil fuel CO2 emissions: Burning buried sunshine

Carbon emissions rising faster than estimates

Global C emissions map

Where emissions come from

Atmospheric CO2:Last 50 years (2.0 ppm/year increase, or 0.5%)

400 ppm

It’s alive! Seasonal cycle

CO2 growth rates

http://www.esrl.noaa.gov/gmd/webdata/ccgg/trends/co2_data_mlo_anngr.png

CO2 growth rates

What do we know aboutgreenhouse gases and past climate change?

Glacial ice “traps” ancient air

Snow accumulates…Snow becomes ice Pore spaces are sealed and

they trap ambient air.

Up to 800,000 year old ice… with ancient trapped air bubbles!

Free air

Trapped air

Atmospheric CO2: Last 250 years

Atmospheric CO2: last 400,000 years!

Atmospheric CO2:Last 50 MILLION years

How unusual are modern CO2 levels?

Carbon fluxes (in Gt/yr), reservoirs (bold, Gt), and residence times (years)

Note: 2010 emissions were 9 Gt / year

1990s data

How much is a gigaton (Gt)?

• One billion metric tons (1012 kg)

• It is about 2750 Empire State Buildings.

• Global C emissions are about 9 Gt as of 2012.

How much does global population weigh?

7 x 109 people x 102 kg/person7 x 1011 kg = 0.7 Gt

AR5 Observed carbon fluxes

Reservoir Pre-Ind Fluxes (Gt/year)

Current Flux (Gt/year)

Photosynthesis -108.9 -123.0

Respiration +107.2 +118.7

Ocean +0.7 -2.3

Fossil fuels emissions +7.8

Land Use changes +1.1

“Other” (volcanoes, lakes, rivers)

+1.0 +0.3

Atmosphere CO2 increase

- 0 - +4

Negative (positive) means removed from (added to) the atmosphere; IPCC AR5 data)

Carbon ins and outs

Source:

Carbon Emissions 7.8 Gt/year

Deforestation 1.1 Gt/year

Sink:

Obs. Atm increase -4.0 Gt/year

Ocean uptake -2.3 Gt/year

“missing sink” -2.6 Gt/year

IPCC AR5 data

Human Carbon emissions

2012 emissions are ~9 Gt… were about 6 Gt when I started teaching this course !

Deforestation accounts for an additional +1.1 Gt / year

Deforestation

- Mainly tropical rainforests

- Cutting down forests to make agricultural land is a net source of carbon to the atmosphere.

CH2O + O2 CO2 + H2O

Bolivia (1984-1998)

Where do our carbon emissions go?

• Ocean takes up about -2.3 Gt / year• Roughly one-third of our fossil fuel emissions

Air (CO2)

Sea (CO2)

CO2 + H2O H+ + HCO3-

Oceanic “Buffer reaction”

Why does the ocean take up CO2?

CO2 gas is soluble in the ocean- Gas solubility is highest in colder water

- CO2 enters the oceans at the poles

- CO2 is converted to HCO3- by “buffer reaction”

- The ocean acidifies as a direct result

Ocean “buffer chemistry” can take up only a finite amount of CO2.

Air-Sea CO2 fluxes

Ocean uptake

Ocean release

Gases are more soluble in COLD water

Ocean uptake

Ocean uptake Ocean release

Net:-2 Gt/yr

Where is our carbon in the oceans ?

Vertical Sections through the oceans

Total ocean uptake is about -2.5 Gt / year

Carbon ins and outs

Source:

Carbon Emissions 7.8 Gt/year

Deforestation 1.1 Gt/year

Sink:

Obs. Atm increase -4.0 Gt/year

Ocean uptake -2.3 Gt/year

“missing sink” -2.6 Gt/year

IPCC AR5 data

What is the “missing sink”

The “missing sink” is the amount of carbon required to balance sources and sinks.

It is a big number: -2.6 Gt Carbon / year !

What is it ???

The Missing Sink (history)

Missing C sink: 1-2 Gt CO2 fertilization

“CO2 fertilization” of high-latitude forests

Plants grow faster/better at higher CO2

But … the effect is assymptotic (not linear)

Atm CO2 level

Plant Cuptake

Other things we need to know

• Not only Fluxes of carbon in/out (Gt / year)

• Sizes of the carbon reservoirs• Residence Time of carbon in each reservoir

• These additional factors determine who the biggest players are and how quickly they will act.

Why these things matter

• What would happen to CO2 levels if we stopped all emissions today?

• What if the ocean warms up a lot?

• What if deep ocean circulation were to change ?

• Does Arbor day matter ?

Ocean and Atmoshere C reservoirs

Atmosphere: 1580 Gt (as CO2)

Ocean C: 39,000 Gt (as HCO3-, CO32-)

Ocean has 50x more carbon than the atmosphere.

Residence time

Residence time is a “replacement time”: time required to affect a reservoir given a certain flux.

(years) = reservoir / input rate

Example: Residence time of a CU undergradReservoir: Size of Columbia’s UG Student

Body?Input rate: Incoming 1st-year class size

Calculating residence time of Carbon due to air-sea exchange

Ocean uptake rate: -2.0 Gt / year

Total Ocean C reservoir : 39,000 Gt

Surface Ocean C reservoir : 600 Gt

C residence time (surface only) = ?

C residence time (whole ocean) = ?

The fate of fossil fuel CO2

Q: How quickly will the planet take up our CO2?

A: Not very quickly…

Fast: “solubility pump” Air-Sea CO2 exchange (centuries)

Moderate: “Deep ocean acid neutralization” (tens of thousands of years)

Really slow: “Weathering of continental rocks” (millions of years)

Fastest response (decades to centuries): The CO2 solubility pump

Air-Sea gas exchange

Medium response time (104 years): Neutralize ocean acidity

Neutralize deep ocean acidity by Dissolving ocean CaCO3 sediments

CaCO3 Ca2+ + CO32-

Really Slow response time (106 years)

Continental weathering (dissolves mountains!)“Urey reaction” - millions of yearsCaSiO3 + CO2 --> CaCO3 + SiO2

75% in 300 years

25% “forever”

Time of removal

Bottom Line

Human C Emissions are large

Nature can’t keep up

Natural C sinks are diminishing

Lifetime of CO2 from your tailpipe:

“300 years, plus 25% that lasts forever”

Radiative Forcing

• Helps us quantify how global climate responds to an imposed change (“forcing”).

What is Radiative Forcing?

Radiative forcing: An imposed change in Earth’s radiative energy balance. Measured in Watts per square meter (W/m2)

• “Radiative” because these factors change the balance between incoming solar radiation and outgoing infrared radiation within the Earth’s atmosphere. This radiative balance sets the Earth’s surface temperature.

• “Forcing” indicates that Earth’s radiative balance is being pushed away from its normal state.

Examples: Solar variability, volcanic emissions, greenhouse gases, ozone, changes in ice cover (albedo), land use changes.

Our first climate model

Recall how to calculate Earth’s effective temperature

The Stefan-Bolzmann equation:

Blackbody radiation I (w/m2) = T4

Earth incoming radiation ( = Earth albedo, or reflectivity)

I incoming = (1-) Isolar = (1-) Tsun4

Is ~0.3, or 30%

Our first climate model

Earth incoming radiation ( = Earth albedo, or reflectivity)

I incoming = ((1-) Isolar ) / 4, or ((1-) Tsun4 )/ 4

Earth outgoing radiation

I outgoing = Tearth4

Earth’s temperature with no greenhouse effect

Teffective = 254.8K (-18°C)

At equilibrium, I incoming = I outgoing

Set Sunlight = Earthlight

Solve for Tearth

Eqn. 3.1 in Archer Chapter 3

Volcanic eruption can change albedo by 1%

= ~30% on average

Teffective = 254.8K

Increase to 31%

New Teffective = 253.9K

or -1°C cooler due a volcanic eruption

Recalling I = (1-) T4

Adding an atmosphere

Greenhouse gases are “selective absorbers”of outgoing long wavelength radiation (Earthlight)

Spectrum of IR light emitted from earth to space

Water Vapor Molecule (H2O)Vibrational modes

H2O bend

H2Ostretch

Carbon Dioxide Molecule (CO2)Vibrational mode (~15µm)

CO2 bend

Natural CO2 radiative forcing

Makes Earth habitable

Pre-Industrial CO2 level of ~280 ppm

Increases surface temperature from -18°C (effective temperature) to +15°C

(Water vapor is also important)

CO2 “Band Saturation”More CO2 warms the Earth less and less

10 ppm

1000 ppm100 ppm

No CO2

Notice the CO2 absorption band

CO2 and surface warming just due to radiation changes - no feedbacks

About 1°C per 100 ppm

Pre-Industrial = 280 ppm

Today = 390 ppm

So, w/o feedbacks: ~1.2°C

With feedbacks: ~3°C

(Feedbacks include water vapor and sea ice changes)

CO2 ppm

Tem

p (K

)

Atmospheric CO2

• CO2 has increased by about +40%• Long term average growth rate is +1.4% per year• Last decade growth rate is +2.0% per year

CO2 (ppm)

All Radiative Forcing factors (1750-2005)

Sum = +1.6 W/m2

Radiative Forcing Contributions

• GHGs warm (CO2, CH4, N2O)

• H2O (vapor) warms

• Tropospheric O3 warms, Strat O3 cools

• Human and natural Aerosols cool

• Solar irradiance warms

Net Effect: +1.6 W/m2