•Concentrations of atmospheric CO2 have risen steadily since ~1800, first due to deforestation for agriculture and wood fuel, then much more dramatically due to fossil fuel combustion.

•Concentrations of CO2 today are about 380 ppm, higher by about 100 ppm than any time in the last 450,000 years.

•Only about 45% of the CO2 emitted to the atmosphere in recent decades has stayed airborne. The rest has been taken up by the growth of plants, and by dissolving in the oceans. The fraction staying airborne declined in the last 10 years, i.e. more uptake took place, and is increasing now (less uptake).

•The trends in fossil fuel use have consistently increased, with some notable changes in 1973 (oil embargo) and recently. The US uses far more per person than other major industrialized countries.

•The most dramatic rise in concentrations of a major greenhouse gas is the near tripling of atmospheric CH4 since 1700. This increase stopped in ~1990. "Radiative forcing" due to CH4 is ~ ½ of that due to CO2. The reasons for the increase in CH4, and the cessation of increase, are hotly debated.

Lectures 11/12: Recent Changes in Atmospheric Composition The global carbon cycle: introduction, fossil fuel use, C reservoirs

06 and 11 March 2008

Course structure: an update

Atmospheric physics: air motions, regional and global circulation; the "first basics" of climate

Atmospheric radiation: shortwave (solar) and longwave(terrestrial) radiation, planetary energy balance, the "greenhouse effect"; the "second basics" of climate.

Climate change: effects of "greenhouse gases" on the planetary energy balance; observations of the climate; the second basics of climate.

Topics in current climate science: hurricanes, floating ice, galciers.

Lectures 1-10 (completed)

11-12Atmospheric composition: the controls on absorption and emission of radiation — and on heating and cooling of the atmosphere

0.1x10-9Carbonyl Sulfide (COS)3.0x10-9Chlorofluorocarbons 0.03x10-6 to 0.3x10-6Carbon Monoxide (CO)0.32x10-6Nitrous Oxide (N2O)0.55x10-6Hydrogen (H2)1.1x10-6Krypton (Kr)1.7x10-6Methane (CH4)5.2x10-6Helium (He)0.02x10-6 to 10x10 –6Ozone (O3)18.2x10-6Neon (Ne)370x10-6 (date: 2000)Carbon Dioxide (CO2)0.0093Argon (Ar)0.04 to < 5x10-3; 4x10-6 -stratWater (H2O)0.21Oxygen (O2)0.78Nitrogen (N2)Mole fractionGasAtmospheric

Composition (average)

red = increased by human activity

1950

1960

1970

1980

1990

Year

History of consumption of fossil fuels.

Emissions have increased by more than 2X since 1970 (8X since 1946). There rise in the last 5 years has been really dramatic.

There has not been a corresponding rise in the annual increment of CO2. In 1970 ~75% of the emitted CO2 stayed in the airborne, but only ~40% in 2000.

3800

6500

Global Fuel Use

7800 in 2005!

The heavier temperature lines 160,000 BP to present reflect more data points, not necessarily greater variability.Source: Climate and Atmospheric History of the past 420,000 years from the Vostok Ice Core, Antarctica, by Petit J.R., Jouzel J., Raynaud D., Barkov N.I., Barnola J.M., Basile I., Bender M., Chappellaz J., Davis J. Delaygue G., Delmotte M. Kotlyakov V.M., Legrand M., Lipenkov V.M., Lorius C., Pépin L., Ritz C., Saltzman E., Stievenard M., Nature, 3 June 1999.

Antarctic Ice Core Data

CO2 varies over geologic time, within the range 190 – 280 ppm for the last 420,000 years. The variations correlate with climate: cold low CO2 . Is CO2 driving climate or vice versa?

Antarctic ice cores compared with modern data for CO2

1 ppm = 2.1 x 109

tons of C (in CO2)

0.0

0.2

0.4

0.6

0.8

CO

2 A

irbor

ne F

rac

1960 1970 1980 1990 2000

CO

2A

irbor

ne F

ract

ion

60 62 64 66 68 70 72 74 76 78 80 82 84 86 88 90 92 94 96 98 00 02

Year-to-year change in CO2 (ppm) (SPO+MLO)/2

Starting year

RECENT GROWTH IN ATMOSPHERIC CO2 CONCENTRATIONS

The average annual increase did not change much between 1970 and 2000, despite significant increases in fossil fuel emissions.

1 ppm = 2.1 x 109

tons of C (in CO2)

Average rate of increase per year, 1.5 ppm = 3.25 x 109

tons/yr—little change (some variations) since 1975.

01

23

Airborne fraction, CO2 (ppm)

Arrows indicate El Nino events

Notice:• atmospheric increase is ~50% of fossil fuel emissions• significant interannual variability

The global cycle of carbon: driving and

moderating CO2 changeThe carbon cycle can be viewed as a set of "reservoirs" or compartments, each characterizing a form of C (e.g. trees; rocks containing calcium carbonate [limestone]).

The cycle of C globally is then represented as a set of transfer rates between compartments.

The total amount of carbon in the atmosphere + ocean + rocks that exchange with the atmosphere/ocean is fixed by very long-term geophysical processes.

Human intervention may be regarded as manipulation of the rates of transfer between important reservoirs.

Composite model of the global C cycle(McElroy, 2001)

Global CO2 cycle

6.3 - 7.3Total

1-2Tropical Deforestation

5.3Fossil Fuel+ cement

Global CO2 budget (PgC yr-1 ) 1980 – 1990 1990 – 2000

Sources

1-2"Missing Sink"

6.3 - 7.3Total

2.1Ocean uptake

3.2Atmospheric accumulation

Sinks

2.1 Pg C = 1 ppm atmospheric CO2 [source: Cias et al., Science 269, 1098, (1995)]Is this budget accurate? What is the scientific basis for these numbers? Why should mid-latitude terrestrial plants absorb anthropogenic CO2?

xxxxxxxxxx When did this uptake begin, can/will it continue?What are the implications of terrestrial uptake for

♦ Future CO2? ♦ US policy? ♦ Climate change?

6.5

.5-1

7-7.5

3.2

1.5-2

1.8-2.8

7-7.5

(Manning and Keeling et al., 2006)

Changes in oxygen track the role of the land vegetation vs. ocean uptake ofanthropogenic CO2.

Land uptake may have decreased at the end of the 1990s, after having increased in the early 1990s.

The US is the largest consumer of fossil fuels. Per capita use is very high, ~5 tons C per person per year. This rate has not changed much in 50 years.

109

met

ric to

ns o

f C /

yr0

.5

1.

1.

5 US fossil fuel use

(source: CDIAC –Trends –updated)

Per Capita Fossil Fuel Use

Japan and Europe…

Why do people in the USA use so much more energy than the rest of the world?

China is projected to have already exceeded US emissions.

Use of fossil fuels in Germany increased rapidly after 1950, per capita use went up about 50%, and all leveled off after 1973.Note the effect of closing inefficient industries in the GDR in 1990. Per capita use in Germany is about 50% lower than in the US.

Germany, combined

Year

Tota

l Em

issi

ons

(Mill

ions

tons

C/y

r)

1800 1850 1900 1950 2000

050

100

150

200

250

300

Total C emissionsPer capita

02

46

Per

Cap

ita (T

ons

C/y

r)

US

Abrupt changes in Japanese fossil fuel use occurred in 1960, when a steep climb started that more than tripled per capita use, and again in 1973, when use leveled out and stayed almost constant for the next 3 decades until the present.

JAPAN

Year

Tota

l Em

issi

ons

(Mill

ions

tons

C/y

r)

1880 1900 1920 1940 1960 1980 2000

050

100

150

200

250

300

Total C emissionsPer capita

01

23

45

Per

Cap

ita (T

ons

C/y

r)

US

Recent trends in CO2 emissions compared to IPCC scenarios

PROJECTIONS OF FUTURE CO2 CONCENTRATIONS[IPCC, 2001]

PROJECTED FUTURE TRENDS IN CO2 UPTAKEBY OCEANS AND TERRESTRIAL BIOSPHERE

IPCC [2001]

Atmospheric Methane (CH4)

Most recent trends in atmospheric CH4

SOURCES OF ATMOSPHERIC METHANE

ANIMALS90

LANDFILLS50

GAS60

COAL40RICE

85

TERMITES25

WETLANDS180

BIOMASSBURNING20

GLOBAL METHANESOURCES (Tg CH4 yr-1)

600

800

700

Scenarios

A1BA1TA1F1A2B1B2IS92a

900

Year

IPCC [2001] Projections of Future CH4 Emissions (Tg CH4) to 2050

2000 2020 2040

Atmospheric CH4: Future Predictions

Constraints on N2O budget changes since pre-industrial time from new firn air and ice core isotope measurements

S. Bernard, T. R¨ockmann, J. Kaiser, J.-M. Barnola, H. Fischer, T. Blunier, and J. Chappellaz, Atmos. Chem. Phys., 6, 493–503, 2006

time1980 1985 1990 1995 2000 2005

300

305

310

315

320

N2O (ppb)mean annual increase 0.74 ppb/yr

N2O versus depth in the Greenland Ice sheet.

N2O in the atmosphere

Human-derived sources are mostly agricultural.

soil

animal_waste

forest_clearing

fossil_f

industry

oceans

N2O is produced as a by-product of bacterial metabolism acting on organic and inorganic nitrogen compounds

Source: GEIA inventory

Agriculture accounts for around 70 per cent of N2O emissions. The sources are mainly from soil micro-organisms that make N2O from nitrogen-rich fertilizers.

kg N2O/ 1x1 grid box

N2O Emissions from soil

Where does human-influenced N2O come from?

Eric Kort, 2008

CFC concentrations in the Atmosphere

Total Chlorine –

all compounds

0%50%200015%50%199915%80%199815%80%1997

0%0%50%80%19960%25%25%50%80%199515%25%25%80%80%199450%75%80%80%1993

80%100%100%199285%100%100%1991

100%1990

1994 Eur. Commun.

1990 US Clean Air Act

1992 Copenhagen amd.

1990 London amend.

1987 orig. treaty

Montreal Protocol: (date, yr)

CFC Phaseout: Allowed Production and Consumption by Developed Countries (% of baseline)

The following slides illustrate some research into the uptake of fossil fuel CO2 by terrestrial vegetation and the

oceans

Regional ocean- and land-atmosphere CO2fluxes, 1992–1996.Orange: Bottom-up land-atm. flux [Pacala, et al., 2001; Kurz and Apps, 1999 N. America; Janssens, et al., 2003, Europe; (Shvidenko and Nilsson, 2003; Fang, et al., 2001, for North Asia];

Cyan: Bottom-up oceanfluxes (Takahashi, et al., 2002),

Blue = ocean-atmosphere fluxes, inverse models,

Green = land-atmosphere fluxes, inverse models,

Magenta = land plus ocean inversion fluxes,

Red: fossil fuel emissions, subtracted from net.

Source: P. Ciais, 2006

The ocean’s capacity to take up CO2 will diminish with time, as the pH of the ocean declines due to uptake of CO2. The ocean becomes acidified.

Uptake of CO2 by chemical dissolution is limited by the rate for exchange between deep ocean water and surface water, and eventually, by acidification of the oceans. Acidification of the ocean is likely to lead to major shifts in marine ecosystems.

Atmospheric release of CO2 from burning of fossil fuels will likely give rise to a marked increase in ocean acidity, as shown in this figure. (upper) Atmospheric CO2 emissions and concentrations, historical (—) and predicted (---), together with changes in ocean pH based on mean chemistry. The emission scenario is based on the mid-range IS92a emission scenario assuming that emissions continue until fossil fuel reserves decline.

10 0.1=25% 100.7 = 5 (!) increase in [H+].

Uptake of CO2 in the US (PgC yr-1) [Pacala et al., 2001]

Forest Trees

Dead wood

soil CWood Prods

Woody encro

achment

fire su

press

Ag s

oils

Net trade

RIver export

Category Low Hi

Forest Trees 0.11 0.15Other Organic Matter

In Forests 0.03 0.15

Domestic Wood Products 0.03 0.07

Woody Encroachment on Non-forested Lands x-fire

0.12 0.13

Agricultural Soils 0.00 0.04

Exports Minus Imports of Food and Wood Products

0.04 0.09

Sediment Burial, River Export 0.04 0.08

Apparent U.S. Sink Including Woody Encroachment

0.37 0.71

Sink (actual net) 0.30 0.58

US "forests": Net sink: 0.3-0.6 PgC yr-1

Emissions (1996): US 1.44Mexico 0.09Canada 0.11

Forests in the US – and many other places – are in middle to young age classes (25-75 years), due to changes in agriculture (intensification) and forest management (intensification).

NH%

of l

and

area

in fo

rest

s20

40

60

80

100

Year

1700 1800 1900 2000

MA

Fitzjarrald et al., 2001

A legacy: land use change in New England

-5

-4

-3

-2

-1

0 NEE = -1.28 - 0.146 x (yr-1990); R2 = 0.337

Year

1992 1994 1996 1998 2000 2002 2004

10

12

14

16-1 x GEE

Resp

GEE = 11.1 + 0.363 x (yr-1990); R2 = 0.732

R = 9.82 + 0.217 x (yr-1990); R2 = 0.626

NEE

(Mg-

Cha-1

yr-1)

Mg-C

ha-1

yr-1

0

20

40

60

80

100

120

Abo

vegr

ound

woo

dy b

iom

ass

(MgC

ha-1

)

93 94 95 96 97 98 99 00 01 02 03 04 05

oakother spp

Year

Rates for growth and for carbon uptake are accelerating in this 80-year-old New England Forest…why is that? Will that continue? How big do North American trees grow?

20 30 50 cm

Year

T (C

)

1900 1920 1940 1960 1980 2000

-35

-30

-25

-20

-15 January

Year

T (C

)

1900 1920 1940 1960 1980 2000

1214

1618

JulyRegional Composite TRegional SmoothedNOBS T

January

Decade

Mon

thly

mea

n Sn

ow (c

m)

1970 1975 1980 1985 1990 1995 2000

2030

4050

60 ThompsonLynnLake

April

Decade

Mon

thly

mea

n Sn

ow (c

m)

1970 1975 1980 1985 1990 1995 2000

510

1520

2530

Changing climate and C: an example from NOBS flux site, Thompson, MB

Snow cover

Temperature

PEAT

45% cover

Deviation from the 9-year means of annual Net Ecosystem Exchange (upper, g C m-2 ), temperature (middle, C), and two-year precipitation sums (lower, cm), illustrating the critical role hydrology plays in determining the annual carbon balance at a mature black spruce forest.

P2 (mm/2yr)

NEE

(kgC

/ha/y

r)

85 90 95 100 105 110 115

-40

-20

020

4060

r2=.72 p<.0035 slope=-3.5

Precipitation (mm in 2 yr)

(gC

m-2

yr-1

)

Upt

ake

|em

issi

on

Annual NEP, 1994-2004

Thompson, MB

T : warmer

Precip: wetter

Water table depth and hydrology are key factors controlling the accumulation or ablation of peat.95 96 97 98 99 00 01 02 03

Year

73

40 4113 12

-11-26 -30

-49-50

0

50

-2

0

2

-15

0

15

1995 1996 1997 1998 1999 2000 2001 2002 2003

-15

0

15

-2

0

2

-50

0

50 Net CO2 echange

Annual T anomaly (oC)

Annual Precip Anom (mm)

But wasn't the weather unusually cold in 2002-2003? Not over the globe….

[base yrs: 1951-1980]

Correlation: {∆T, ∆ soil moisture index}CCSM1-Carbon Control Simulation

DJF JJA

Positive correlation warmer-wetter; or cooler-drier

Negative correlation warmer-drier; or cooler-wetter

slide courtesy Inez Fung [I. Fung, S. Doney, et al.]]

•Concentrations of atmospheric CO2 have risen steadily since ~1800, first due to deforestation for agriculture and wood fuel,then much more dramatically due to fossil fuel combustion. Concentrations of CO2 today, about 378 ppm, higher by about 100 ppm than any time in the last 450,000 years.

•Only about 45% of the CO2 emitted to the atmosphere over the past decade has stayed airborne. The rest has been taken up by the growth of plants, and by dissolving in the oceans. The fraction staying airborne has actually declined in the last 10 years, thus more uptake is currently taking place.

Lectures 11/12: Recent Changes in Atmospheric Composition The global carbon cycle: introduction, fossil fuel use, C reservoirs

06 and 11 March 2008

•The trends in fossil fuel use have consistently increased, with some notable changes in 1973 (oil embargo) and recently. The US uses far more per person than other major industrialized countries.

•The most dramatic rise in concentrations of a major greenhouse gas is the near tripling of atmospheric CH4 since 1700. This increase stopped in ~1990. "Radiative forcing" due to CH4 is ~ ½ of that due to CO2. The reasons for the increase in CH4, and the cessation of increase, are hotly debated.

•Future changes in the biosphere can have important effects on climate change, and vice versa.