THE CARBON CYCLE

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Directions:

Read Chapter 5, listen to the video lecture for Ch. 5, and answer the questions below. Proper writing and clarity are important in earning full credit.  Please use complete sentences and double space the answers.

 

More to Read:
  1. What is the unit of atmospheric CO2? Explain what it means with a numeric example. (3 points)

 

  1. What is the current level of globally averaged CO2 concentration in the atmosphere “now”?  Include the month and year of the data from this link in your sentence –>https://www.esrl.noaa.gov/gmd/ccgg/trends/global.html) (1 point)

 

  1. List 2 other greenhouse gases that contain carbon (C): (2 points)

 

  1. According to Fig. 5.1, what season in the Northern Hemisphere has the highest CO2 concentrations and why? What season has the lowest CO2 concentrations in the Northern Hemisphere and why? (4 points)

 

  1. What are 4 atmospheric sources of CO2 and list whether they’re natural or anthropogenic. (8 points)

 

  1. What is the unit of measurement or estimation of the amount of carbon in a particular carbon reservoir? (1 point)

 

  1. Not including Earth’s crust, what ‘sphere’ or reservoir contains the most carbon? (1 point)

 

  1. What is the carbon ‘turnover time’ or ‘residence time’ for a) the atmosphere, and b) the deep oceans. Show your work and explain what each one means in more laymen’s terms. Don’t forget units. (6 points)

 

  1. What is the rate of exchange of C from rocks to the Atmosphere-Ocean-Land-biosphere? (1 point)

 

  1. What is the average rate of human C emissions into the atmosphere from Earth’s crust? (1 point)

 

  1. Explain 2 ways humans are disturbing the C-cycle and creating an imbalance in the natural C-cycle. (4 points)

 

  1. Explain 2 ways that scientists are confident that the increased CO2 emissions is from human sources and the burning of fossil fuels. (4 points)

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  1. Watch this animation from the National Oceanic and Atmospheric Administration’s Global Monitoring Division about the history of CO2 from the last 800,000 years:

Carbon Dioxide Trend Animation （https://www.esrl.noaa.gov/gmd/ccgg/trends/history.html）

What are two interesting things in the CO2 animations that caught your attention? （about 100 world）

THE CARBON CYCLE Metr 112 – Global Climate Change

Introduction to Modern Climate Change

Chapter 5

GREENHOUSE GASES AND OUR ATMOSPHERE’S COMPOSITION

WELL-MIXED ATMOSPHERIC GASES

Composition of the Entire Atmosphere: Dry Air Percent by Volume:

  • Nitrogen: 78%
  • Oxygen: 21%
  • Argon: 0.9%
  • Water Vapor: Varies at 0-4% (depending on conditions)
  • Trace Gases: 0.1%
  • Carbon Dioxide: 0.04%

– Neon: 0.002%

– Methane: 0.00017%

A GREENHOUSE GAS (GHG) IS A GAS THAT IS LARGELY TRANSPARENT TO THE SUN’S UV

AND VISIBLE RADIATION BUT ABSORBS AND REEMITS LONGWAVE THERMAL IR RADIATION

THAT IS EMITTED FROM EARTH.

Natural GHGs • Water Vapor (H2O[g]) • Carbon Dioxide (CO2) • Methane (CH4) • Nitrous Oxide (N2O) • Naturally occurring tropospheric O3

Anthropogenic GHGs • CFCs • HCFCs • HFCs • Tropospheric O3 from urban smog • Additional and unnatural CO2 , CH4,

and N2O emissions

A b

so rp

ti on

Pe

rc en

ta g

e

Natural Greenhouse Gas Radiation Absorption

Absorption Spectral Bands

CH4

NO2

O3

H2O (vapor)

CO2

TOTAL

Natural Greenhouse Gas Radiation Absorption

NOT ALL GHGS ARE CREATED EQUAL

  • Chemical Lifetime is the lifetime that a molecule can exist in the atmosphere until broken apart through a chemical reaction.
  • It tells us how carbon moves between the atmosphere, ocean, land biosphere, and rocks on the Earth.

Chemical

GLOBAL WARMING POTENTIAL (GWP)

Global Warming Potential (GWP) was developed to allow comparisons of the global warming impacts of different GHGs.

A measure of how much energy the emissions of 1 ton of a gas will absorb over a given period of time, relative to the emissions of 1 ton of carbon dioxide (CO2)

Everything is relative to CO2, which always has a GWP of 1

3 Factors that go into GWP are:

  • Absorption strength • Chemical Lifetimes • Atmospheric Residence times

IPCC’s 100-year GWPs

91% OF GHG EMISSIONS

ARE CARBON BASED!

ATMOSPHERE – LAND BIOSPHERE –

OCEAN CARBON EXCHANGE

EARTH’S SPHERES AND MAJOR CARBON STORAGE RESERVOIRS

WHERE IS MOST CARBON FOUND ON EARTH?

PARENTHESES = %

Joshi, Niraj & Maharjan, Keshav. (2013). Climate Change, Agriculture and Rural Livelihoods in Developing Countries. 10.1007/978-4-431-54343-5.

ATMOSPHERE – LAND BIOSPHERE EXCHANGE

PHOTOSYNTHESIS VS. ANIMAL RESPIRATION

Equations from (Dessler, page 70)

CH2O + O2 Carbohydrate (energy for plant)àCO2 + H2O + sunlight

Photosynthesis:

CO2 + H2O + energyàCH2O + O2

Human and Animal Respiration:

PERMAFROST

  • Ground, including rock or soil, at or below the freezing point of water (0 °C) for two or more years.
  • Forms in the polar areas.
  • Melting/thawing of permafrost releases large amounts of methane!.

METHANE BURNING FROM HOLE IN PERMAFROST IN ALASKA

Methane, a potent greenhouse gas, is bubbling from thawing ground under lakes across the Arctic. In winter, surface ice traps the gas. On this pond near Fairbanks, Alaska, scientists have drilled through the ice and set the escaping methane on fire.

PHOTO BY KATIE ORLINSKY https://www.nationalgeographic.com/environment/2019/08/arctic-permafrost-is-thawing-it-could-speed-up-climate-change-feature/

NH PERMAFROST AREA • About 58 percent of the land in the Northern Hemisphere surrounding the Arctic Circle is permafrost.

THE THAW SPEEDS UP

The unexpectedly rapid collapse of ice-rich permafrost in the Arctic could pump billions

of additional tons of methane and carbon dioxide into the atmosphere every year—a threat that has yet to be fully accounted for

in climate models.

Scientists are discovering destabilized landscapes where permafrost that once

thawed a few inches a year can now abruptly thaw up to 10 feet within days or weeks, creating wetlands in once frozen

regions and accelerating emissions from up to 1,600 gigatons of carbon still locked

underground.

how-abrupt-permafrost-thaw-threatens-arctic-feature/

A LANDSCAPE REVOLUTION

As ice buried within frozen ground melts, the

meltwater moves through the permafrost, thawing it

further and causing the ground above it to slump.

Ponds form and later drain, hastening the

collapse of even more frozen soils. The process

is called abrupt thaw, and it’s accelerating the release of trapped

carbon—and visibly changing the Arctic.

nment/2019/08/how-abrupt-permafrost- thaw-threatens-arctic-feature/

ATMOSPHERE – OCEAN EXCHANGE

OCEAN ACIDIFICATION

Dissolved CO2 into water creates dissolved carbonic acid (H2CO3) -Lowers pH of Oceans (becomes slightly more acidic)

CORAL BLEACHING

Coral Bleaching in the Great Barrier Reef

https://www.cnn.com/2017/04/10/asia/great-barrier-reef-coral-bleaching/index.html

EXPLANATION OF CO2 DISSOLVING INTO SEA UNDER PRESSURE (MORE CO2 IN ATMOSPHERE)

WITH SODA CAN ANALOGY

TURNOVER TIME

  • “Turnover time” (T) (also called global atmospheric lifetime) is the ratio of the mass (M) of a reservoir (e.g., a gaseous compound in the atmosphere) and the total rate of removal (S) from the reservoir (IPCC):
  • T = M / S.
  • For each removal process, separate turnover times can be defined. In soil carbon biology, this is referred to as Mean Residence Time.”
  • Turnover time = “lifetime” = “residence time”
  • Reservoir = “pool”
EXAMPLE OF TURNOVER TIME: C IN ATMOSPHERE

What is the turnover time/residence time of a carbon atom in the atmosphere?

Turnover time (T) = Mass of reservoir (M) Removal rate (S)

Removal rate = Total fluxes out (Dessler)

Turnover time (T) = 850 GtC 200 GtC/yr

= 4.25 years

Matm = 850 GtC Satm = 120 GtC/yr + 80 GtC/yr = 200 GtC/yr

4.25 years is how long a carbon atom stays in the atmosphere on average before transferring to either the biosphere or the ocean.

EXAMPLE 2 OF TURNOVER TIME

What is the turnover time/residence time of carbon in the deep ocean?

Turnover time (T) = Mass of reservoir (M) Total Fluxes Out (S)

Turnover time (T) = 40,000 GtC 100 GtC/yr

T = 400 years

M = 40,000 GtC

S = 100 GtC/yr

ATMOSPHERE-ROCK EXCHANGE

ATMOSPHERE-ROCK EXCHANGE

  • Most Carbon is ‘locked’ away in the earth’s crust (i.e. rocks) as
  • Carbonates (containing carbon)
  • Chemical Weathering • Breakdown of rock by

acidic rain

  • Only 0.1 GtC/yr go into rocks.

ATMOSPHERE-ROCK CARBON EXCHANGE

  • Most C in the world is stored in rocks, such as limestone (CaCO3), and this carbon is slowly exchanging with the atmosphere- land biosphere-ocean system.
  • Exchanges are roughly balanced at only 0.1 GtC/yr between Earth’s crust and the [Ocean-Atmosphere-Biosphere].

oceanà• Sources of CO2 into rocks: • Chemical Weathering of Rocks

sediment.

  • Natural Plant Decay

Volcanic Eruptions

Chemical Weathering of Rocks; Plant decay

Turnover time = 46,000/(0.1) = 460,000 years.

CARBON STORAGE RESERVOIRS AND RATES OF EXCHANGE

(white #s) = Carbon storage amount in Gigatons (GtC)

1 Gt = 1 billion metric tons

yellow #s = Carbon fluxes (GtC/yr) = ‘annual avg. C fluxes’

Red = annual avg. human emission C fluxes

– photosynthesis and respiration balance out – natural air-sea C exchange roughly balances out also. ***45% of human emissions stays inside the atmosphere.

HOW ARE HUMANS PERTURBING THE CARBON

CYCLE?

HOW ARE HUMANS PERTURBING THE CARBON CYCLE?

  1. Burning of Fossil Fuels
  2. Deforestation (agricultural, land development reasons)
  3. Cement Production 4. Agricultural

practices (soil tilling; biomass burning)

***Burning fossil fuels is adding C into the atmosphere 80 times more per year than the natural way!

VARIOUS SOURCES AND SINKS OF CO2

  • A sink is a process or something that removes a gas from a defined storage reservoir (e.g., atmosphere, upper oceans, deep oceans, earth’s crust, etc.).
  • The red arrows (image) are the main CO2 sinks.
  • The black arrows are the main CO2 sources (natural and anthropogenic) into the atmosphere.

AUGUST 2019 : 409.95 PPM Short-term CO2 Trends

CO2 TRENDS

Average carbon dioxide abundance if all of the carbon dioxide emitted by human activities since 1959 had remained in the atmosphere.

Last 10,000 yrs

Last 50 yrs

Last 250 yrs

HOW DO WE KNOW THE BURNING OF FOSSIL FUELS IS THE MAIN SOURCE FOR THE OBSERVED CO2

INCREASE?

NOAA Earth System Research Laboratory/ Global Monitoring Division (CO2 annual increase), the solid line is from Denman et al., 2007, Figure 7.4).

A COMMONLY ASKED QUESTION ABOUT THE

CARBON CYCLE

HOW DO WE KNOW THE BURNING OF FOSSIL FUELS IS THE MAIN SOURCE FOR THE OBSERVED CO2

INCREASE?

CARBON ISOTOPES! • C-12 (6 p, 6n)

  • Plants prefer! • 99% of C • Most C in fossil fuel is C12
  • C-13 (6 p, 7 n) • 1% of C

Scientists measure the fraction of C13/C12 in the atmosphere and have been keeping records!

Gosh et al, 2003

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ce nt

ag e

d ec

re as

e in

C 13

fr

om a

tm os

p he

ri c

C O

2

C12 is increasing in the atmosphere relative to C13 because of burning fossil fuels

THE LONG-TERM FATE OF CARBON DIOXIDE Desser Fig 5.9 Page 84

METHANE

METHANE (CH4) • Simplest and most abundant

organic gas.

  • GWP of 28-30
  • Largest human sources:
  • Agriculture
  • LIVESTOCK IS LARGEST SOURCE
  • Rice Farming
  • Waste/landfills
  • Petrochemical Industry

GLOBAL CH4 TRENDS

CHAPTER SUMMARY

Only a few components of our atmosphere are greenhouse gases, which absorb infrared radiation.

The carbon cycle describes how carbon cycles through its primary reservoirs.

The atmosphere exchanges carbon with the land biosphere through photosynthesis and respiration.

The atmosphere-land biosphere-ocean system also exchanges carbon with rock reservoirs.

Humans are perturbing the carbon cycle by extracting and burning fossil fuels.

It takes a long time for the carbon cycle to remove carbon that humans add to the atmosphere.

Methane is another important greenhouse gas as each molecule of methane has the warming power of ~20 carbon dioxide molecules.

  • The Carbon Cycle
  • Greenhouse gases and our atmosphere’s composition
  • Well-Mixed Atmospheric Gases
  • A greenhouse gas (GHG) is a gas that is largely transparent to the Sun’s UV and visible radiation but absorbs and reemits longwave Thermal IR radiation that is emitted from Earth.
  • Slide Number 6
  • Slide Number 7
  • Not All GHGs are Created Equal
  • Global Warming Potential (GWP)
  • Slide Number 10
  • Atmosphere �– land biosphere –�ocean �carbon exchange
  • Earth’s spheres and major Carbon Storage Reservoirs
  • Where is most Carbon found on Earth?��Parentheses = %
  • Atmosphere – land biosphere exchange
  • Photosynthesis vs. Animal Respiration
  • Permafrost
  • Methane burning from hole in permafrost in Alaska
  • NH Permafrost Area
  • The �thaw speeds up
  • A landscape revolution
  • Atmosphere – ocean exchange
  • Ocean Acidification
  • Coral Bleaching
  • Explanation of CO2 dissolving into sea under pressure (more CO2 in atmosphere) with soda can analogy
  • Turnover Time
  • Example of Turnover Time: C in Atmosphere
  • Example 2 of Turnover Time
  • ATMOSPHERE-ROCK EXCHANGE
  • ATMOSPHERE-ROCK EXCHANGE
  • Atmosphere-Rock Carbon Exchange
  • Carbon Storage Reservoirs and Rates of Exchange
  • How are humans perturbing the Carbon Cycle?
  • How are humans perturbing the Carbon Cycle?
  • Various sources and sinks of CO2
  • August 2019 : 409.95 ppm
  • CO2 Trends
  • How do we know the burning of fossil fuels is the main source for the observed CO2 increase?
  • A commonly asked question about the Carbon Cycle
  • How do we know the burning of fossil fuels is the main source for the observed CO2 increase?
  • The long-term fate of carbon dioxide
  • Methane
  • Methane (CH4)
  • Global CH4 Trends
  • Chapter summary

Last Updated on April 4, 2020

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