February 19February 19Land Use and Cover Change and the Land Use and Cover Change and the Global Carbon CycleGlobal Carbon Cycle

Ecological Disturbance on a Global ScaleEcological Disturbance on a Global Scale

Global Change / Climate Change Global Climate change which results from

human activities is one of the most contentious topics in environmental science and policy

There is growing agreement that: There is a climate change occurring That humans are the cause

The global carbon cycle is a keystone topic

The carbon cycle The carbon cycle is the canonical global change issue, especially when we

want to “go beyond climate change” think: is it the most important, in our time?

I want to use this as a good overview issue for human impacts on the planetary scale strong geographical component strong human component, many leads and connections to human

dimensions strong policy component it’s a big mystery but something important to find answers to if we cant understand something this basic we wont be able to do much

else points to all the classical issues of inquiry: measurement, models,

evidence, inference, uncertainty,etc social science needs to know this stuff

The greenhouse effect Based only on our distance from the sun, the

earth should be colder by 33 degrees C. Our planet should be a chunk of ice But natural greenhouse gases – primarily carbon

dioxide and water vapor provide for heating of the planet to a normal temperature.

But we are now introducing MORE greenhouse gases, and we don’t know what affect this will have

78% Nitrogen78% Nitrogen

21% Oxygen21% Oxygen

<<0.04% Carbon Dioxide0.04% Carbon Dioxide

Atmospheric GasesAtmospheric Gases

Carbon dioxide in the atmosphere Exists in trace quantities This means doubling or halving can be

important Consider oxygen: if all trees were removed

the oxygen concentration would decline by 300 ppm – from 209,480 to 209,180.

But an increase of 300 ppm for carbon dioxide would double it.

Other Greenhouse Gases And Sources Water vapor Methane Nitrous oxide CFC’s and other

halocarbons

Hydrological cycle Animal husbandry Chemical fertilizers* Refrigerants*

* = Long residence times and contribute toozone depletion

The greenhouse effect

Global Surface Temperatures

NOAA Global Flask Sampling Network

Years before presentYears before present Petit et al. (1999)Petit et al. (1999)

CO

CO

22-co

ncen

trat

ion

(ppm

)-c

once

ntra

tion

(pp

m)

200200

240240

280280

320320

360360

160160

1750

2000

00100,000100,000200,000200,000300,000300,000400,000400,000

Atmospheric [CO2] over the last 400,000 years

HistoricallyTotal emissions of C

[deforestation and fossil-fuel burning]

450 PgC

From 1850 to 1990

Houghton et al. 1999, Houghton 1999, Defries et al. 1999, IPCC-TAR 2001

Global Emissions from Land Use Change

[180-200 PgC from land use change]

+ 90 ppm CO2 in the atmosphere

[40 ppm due to changes in land use]

90% due todeforestation[20% descrease

Forest Area]

124 Pg emitted due to land use change60% in tropical areas

%40 in temperate areas

1 Pg C = 1,000,000,000,000,000 g C(a billion tones)

7.9 Pg C/yr (6.3 Pg Fossil Fuel)(1.6 Pg Land Use)

2.9 PgC/yr - Oceans

1.3 PgC/yr - Terrestrial Ecosystems

3.7 PgC/yr - Atmosphere

Global Carbon Budget - The fate of CO2Period 1990-1996

After IPCC, TAR 2001

Global CO2 Budgets (Pg/yr)

Atmospheric Increase +3.3±0.1 +2.9 ±0.1

1980’s 1990-95

IPCC, TAR 2001

Land-Use Change(80’s) +1.6 (0.5 to 2.4)

Land-Atmosphere Flux -0.2 ±0.7 -1.0 ±0.6Ocean-Atmosphere Flux -2.0 ±0.6 -2.4 ±0.5Emissions (fossil fuel, cement) +5.5 ±0.3 +6.3 ±0.4

Residual Terrestrial Sink - 1.8 (-3.7 to +0.4)

dA = F + B - O - b

1980s3.7 = 6.3 + 1.6 - 2.9 3.7 5.0 (Difference is 1.3 -- The Missing Sink)

1990s2.9 = 6.3 + 1.6 – 2.42.9 Difference is 2.6)

Global Carbon Sinks resulting from land use/cover change

NOAA-CMDL 1999

Location of Global C Sources and Sinks

CO2 Flask Network and Inverse Modeling

- Atmospheric constraints of Global C sources and sinks -

Inverse Model Estimates of CO2 Uptake (7 Models)

IPCC, TAR, 2001

- 0.7 to - 2.4 Pg C/yr

+ 1.6 Pg C/yr

Biological C Sources and Sinks

- 1.6 Pg C/yr0.0 Pg C

- 0.0 Pg C/yr

Fan et al. 1998

Inverse Modeling Calculations of C Sources and Sinks

North America: 1.6 PgC/yr Euroasia: 0.5 PgC/yr

- 0.1

- 0.5 - 0.3 - 1.3

Ciais et al 2000

TM21985-1995GlobalView-CO2

Inverse Modeling Calculations of Terrestrial Carbon Sources and Sinks

Pg C/yr

Current Terrestrial Sinks Potential Driving Mechanisms

CO2 fertilization Nitrogen fertilization Climate change Regrowth of previously harvested forests

Reforestation / Afforestation Regrowth of previously disturbed forests

Fire, wind, insects Fire suppression Decreased deforestation Improved agriculture Sediment burial Future: Terrestrial Carbon Management (e.g., Kyoto)

Land Use/Cover Change

• The Northern Hemisphere Temperate/Boreal

Sink• The Eastern USA sink• China sink

Carbon SinksThree Examples:

1. Northern Hemisphere Carbon Sink Late 80’s-Early 90’s

Goodel et al 2001 (in press)

- Forest Inventories and Land Use Change as constraints of C Sources and Sinks -

Total Sink: 0.7 to 2.4 Pg C/yr[Inverse modeling] 30-100%

70% in Temperate Regions[Larger sink in Euroasia than in North America]

[Forestry Sector]

0.7 to 0.8 Pg C/yr

0.2 Pg C yr-1 in living biomass, 0.4 Pg C yr-1 in dead organic matter0.1 Pg C yr-1 in forest products

Carbon Stocks in Live Forest VegetationOver the Last Half Century

1950 1960 1970 1980 1990 2000

30

25

20

15

10

5

0

Live

Veg

etat

ion

(Pg

C)

Canada

Coterminous USEuro Russia

China

Asian Russia

Europe

Goodel et al 2001 (in press)

2. Eastern United States Carbon Sink

Eastern United States (5 states)

96% of the C sink attributed to land use change:• Forest regrowth after crop abandonment• Reduced harvesting• Fire suppression

Caspersen et al. 2000

4% remaining attributed to:• Increasing CO2

• Nitrogen Deposition• Climate Change

3. Changes in Forest Biomass C storage in China1949-1998

Fang et al. 2001

Between 1940’s and 70’s, C storage declined by 0.68 Pg C due to

forest exploitation policies

From late 1970’s to present, C storage has increased by 0.4 Pg C

due to policies of protection and timber production[+ 0.021 Pg C/yr]

0.38 Pg C comes from planted forests

Nepstad et al. 1999

Landsat TM image, Paragom.,1991, classified as forest and non-forest[Brazilian Government reportingmethodology] – 62% Forest

Same image,classified after ranch owners interviews:only 1/10 of the above forest was Classified as undisturbed forest by human practices – 6.2% Forest

Forest Conversion: Carbon Density

Forest Impoverishment:

- Surface fires (could be responsible for doubling C emissions during El Nino years)- Logging (4-7% of that of forest conversion)

Forest Structure: Carbon Sink Strength

time

BiomassSink

Strength

Carbon Source: Emissions from Forest FiresDirect C emissions from Fires in Canada (1950-1999)

Amiro et a l. 2 0 0 0

P hot

o: M

. Fla

nnig

a n, C

a na d

a

Area burned in the North AmericaBoreal Forest Region (1940-1998)

Kasischke and Stocks 2000

Annual global carbon emissions from vegetation fires1.6 Pg C/yr

25% of the amount of fossil fuel emissions

Fire exclusion has increased C storage in forests [last 100 yrs]

Carbon Sink: Fire suppressionP h

otos

: M. F

lan n

igan

[Can

ada]

Total Area Burned (US)

Houghton et al. 2000

Annual Flux of C (TgC yr-1)

Eliminating fire completely,US forest could accumulated

2.6 Pg C by 2140

Woody Biomass

PrecipitationWater Availab.Soil toxicitiesAir temperature

+ +-

Woody Encroachment:Biophysical and land management drivers

After Scholes and Hall 1996

- -

Fire Browsers Harvesting

Overgrazing+ +

+--

-

Nutrients Human population+ +

N depositionIncreasing CO2

Phot

o: S

. Ar c

h er

Woody EncroachmentPh

oto:

Mar

tin 1

975,

Ariz

ona

1903

& 1

941

Woody plant encroachment has promoted C sequestration in grassland and savanna ecosystems of N and S America,Australia, Africa, and Southeast Asia over the past century.

Maximum Potential C sequestration in the absence of fire = 2 Pg C yr-1 (upper value) Scholes and Hal 1996 Estimated CO2 sink:

• USA: 0.17 PgC/yr for the 1980s (Houghton et al., 1999)

• Australia: 0.03 PgC/yr (Burrows, 1998)

Improved Agriculture Practices

Donigian et al. 1994 , Lal et al. 1998, Metting et al. 1999, IPCC Land Use and Forestry 2000

• High yielding plant varieties• Fertilisers• Irrigation• Residue management• Reduced tillage for erosion control

has contributed to the stabilisation or enhancement of carbon stocks

0

10

20

30

40

50

60

70

Max

imum

Yea

rly C

Mitig

atio

n Po

tent

ial (

Tg C

y-1

)

0

1

2

3

4

5

6

% O

ffset

of 1

990

Euro

pean

CO

2 Em

issio

ns

Land Management Change

Animalmanure Sewage

sludge

StrawIncorp.

No-till

Bioenergyproduction

Woodlandregeneration

Extensification

Carbon Mitigation and Offsets due to Land Management in Europe

A combination of best practices could offset 0.113 Pg C/ yr.

Over 100 years this is equivalent to a C offset of 11.3 Pg.

• In the USA:

Full adoption of best management practices would be likely to restore soil organic carbonlevels to about 75-90% of their pre-cultivation level, increasing 7.5-20.8 Pg C over 100 years (0.075 to 0.208 Pg C per year).

Example from the tropics

Main points Land use and management leaves a mosaic of various

cover types and cover states These systems have memory Memory is manifested in long term sources, and sinks in

regrowth and soil OM storage Memory is also manifested in how many cycles or

transitions a landscape patch has undergone alteration Changes in stocks – changes in area, changes in density --

and changes in fluxes, which vary with time

Geography and timing Some important issues include geography and timing

Geography in the broader context to include spatial pattern

Past deforestation may currently be regenerating; in regions where current deforestation is declining and there are larger regenerating areas (reflecting a history of large deforestation rates), such asynchronies may be important.

Considerable evidence for large areas of regeneration, and for considerably variable rates of clearing

Multiple changes in one landscape

The current landscape is a mosaic, or record, of current and past land use and cover changes

Variation exists at fine temporal and spatial scale Variation exists across classes of cover (from conversion)

and within classes of cover (from modification or degradation)

History has created a more complex landscape We know nothing about the processes which form this

landscapes over time, nor do we have good measures (maps) of these landscapes themselves.

Our prognostic ability is severely limited

Observations: extent and density

We focus on making direct observations of changes in forest extent (both increase and decrease) and density

This can be done using annual observations from high spatial resolution remote sensing in conjunction with a coupled land use-carbon models.

This approach complements, but is more direct in determining the land use component, than use of other measures of changes in forest carbon from stand inventory data alone (Casperson et

al. 2000)

Inter-annual variation in rates of Inter-annual variation in rates of deforestation and regrowthdeforestation and regrowth

0

5

10

15

20

25

30

35

75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97

Carbon flux over space

3.8

0.91.5

6.2

-0.5

5.3 5.5

4.6

7.2

-1

0

1

2

3

4

5

6

7

8

1 2 3 4 5 6 7 8 9

Year

Net

Flu

x

Carbon flux over time

Example from North America

1938 1955 1996

1938 1955 1996

1938 1955 1996

The urban-agriculture interface has grown trees as it expands(and the urban-forest interface has cut and fragmented trees)

Some other objectives of interest…

…or confusion

Forest edges: biomass collapse Tropical sources from mortality Tropical sinks from regrowth Tropical and Global sinks from space Logging

  Formation Rate 

Eradication Rate 

Total Flux (F1999)

Annual Flux 1999

  Constant Compounding Constant Compounding Tg C Tg C yr-1

1 x   x  35.308 0.693

2   x x  35.240 0.701

3 x     x72.882 1.641

4   x   x72.742 1.599