Download Lecture`Outline` Biogeochemical`Cycles`

Lecture'Outline'
•  The$Global$Carbon$Cycle$and$Carbon$Fluxes$
–  Sources'and'Sinks'for'Atmospheric'C'
–  Time'scales'of'C'exchange'
–  Carbon<Climate'Feedback'Systems'
•  Changes$to$the$“Natural”$Carbon$Cycle$
–  Fossil'Fuels'and'Land'Use'Change'
–  An'imbalanced'system'
Biogeochemical'Cycles'
Re(cycling)'of'elements'within'the'Earth'System'is'essenFal'for'
maintenance'of'a'living'planet.'
EssenFals'for'life'
–  Water:'hydrologic'cycle'
–  Energy/sunlight:'radiaFve'balance'
–  Carbon:'building'block'of'life.'
!  Carbon'100x'more'concentrated'in'living'maNer'
!  Carbon'cycle:'biophysical'processes'that'recycle'carbon'
among'the'components'of'the'Earth'System'
–  Nutrients:'Nitrogen,'Phosphorous,'etc.'
Inputs'to'Atmospheric'Reservoir'
(all'carbon'containing)'
•  Carbon'Dioxide'(CO2)'
•  Methane'(CH4)'
•  Fluorocarbons'(including'CFCs)'
'
CO2:'So'Simple…yet'
Natural,'colorless,'odorless'gas'
'
Not'associated'with'aestheFc'“polluFon”'issues'
Carbon'(C),'the'4th'most'abundant'element'in'the'Universe'
'
Global'Warming'PotenFal'(GWP)'
Strength'of'a'given'mass'of'greenhouse'gas'to'posiFve'radiaFve'
forcing'over'a'specific'Fme'scale'(typically'100yrs)'relaFve'to'
equivalent'mass'of'carbon'dioxide.'
'Factors'to'consider'
–  wavelength'(opaqueness'of'atm'at'given'wavelength)'
–  RadiaFve'efficiency'
–  atmospheric'lifeFme'
Greenhouses'Gases:'Carbon'Dioxide'
The'Notorious'CO2'
'
Natural$Sources:'vegetaFon,'fires,'ocean,'
volcanoes.'Part'of'the'carbon'cycle'
(photosynthesis/respiraFon)'
'
Anthropogenic$Sources:'Incomplete'combusFon'
of'fossil'fuels,'biomass'burning'
'
Life@me:'20<100'years'
'
GWP:$1'(by'definiFon)'
'
Greenhouses'Gases:'Methane'
'
•  Natural$Sources:'peat'bogs,'soil'
•  Anthropogenic$Sources:'Industrial'and'auto'
emissions,'agriculture'(belch!)'
•  Life@me:'10<20'years'
•  GWP:$25''
Fluorocarbons$
CFCs:'SyntheFc'compound'of'ozone'hole'notoriety'
Replaced'by'HFCs'and'PFCs'
'
Natural:'None'
'
Anthropogenic:'Refrigerants,'propellants,'solvents'
'
Life@me:'100y'to'1000y'
'
GWP:$5000'to'25000'
'
Carbon'Reservoirs'
Total carbon reservoir on Earth = 1x1023g : 1x108 GT
Carbon'Fluxes'
Flux: exchange between reservoir
Photosynthesis
60 Gton/yr
Respiration and
Decomposition
60 Gton/yr
Atmospheric'CO2'
600'Gtons'
Steady State: balanced inflow/outflows, constant over time
Atmosphere'as'Transfer'StaFon'for'C'exchange'
Carbon'bathtub:'Nat'Geo'12<09'
Residence'Time'
Residence'Time'(yr)'
='average'amount'of'Fme'a'substance'stays'in'a'given'reservoir'at'
steady'state'(also'can'be'calculated'by'half<lives)'
=''amount'in'reservoir'(g)'
'
' input or output rate (g/yr)
Example:'Water'Vapor'Residence'Time'
–  Global'Mean'Water'Vapor':'2.5cm'
–  Global'Mean'PrecipitaFon'Rate':'2.5mm/day'
'
Residence'Fme'determines'speed'of'carbon'cycling'
Try'this'out'for'photosynthesis/respiraFon'
'
Where'is'most'of'the'carbon'today?'
Answer:'In'the'Lithosphere'(10,000x'ATM)'
'
•  Most'Carbon'is'‘locked’'away'in'the'crust'
–  Carbonates'(containing'carbon),'i.e.'
Limestone'(CaCO3)'
–  Inorganic'Carbon'(non<living)'
•  Carbon'was'once'living,'therefore'the'term'
“fossil'fuel”'comes'from'the'fossilized'
sediments'in'rock'
#2'Reservoir:'Global'Oceans'(50x'atmosphere)'
'
Other'Carbon'Reservoirs'
Vegeta@on$(1x$ATM)$
•  carbon'='life'for'plants''
•  rhythm'of'season'(later)'
•  forests'store'>85%'of'veg'carbon'
'
'
Soils$(2x$ATM)$
•  decomposing'plants'+'roots'
•  mostly'stored'in'climate'where'
precipitaFon>evapotranspiraFon''
•  boreal'ecosystems,'forests'
•  Increases'in'evaporaFon'in'a'
warming'climate'might'limit'the'
ability'of'soils'to'“hold”'carbon'
Global'Carbon'Cycle'
1.'Carbon'is'conserved'
'Total'carbon'of'Earth:'fixed'
'Steady'State'implies'that'for'each'reservoir''
' 'Input'='Outputs'
'
2.'Hierarchy'of'cycling'across'reservoirs'and'Fmescales'
Short'term'cycle'(seconds'to'years)'
Long'term'cycle'(years'to'thousands'of'years)'
3.'Currently'not'in'steady'state'due'to'man<made'inputs'
Global'Carbon'Cycle'
Source'or'Sink:'Reference'Frame'Atmosphere'
•  Source'<'a'process'that'puts'carbon'into'the'atmosphere'''
–  Fossil'fuel'combusFon''
–  Plant'respiraFon'
–  Fire'and'volcanic'emissions'
'
•  Sink'<'a'process'that'takes'up'carbon'from'the'atmosphere'
–  Plants/vegetaFon'(long'lived'trees)'
–  Burial'of'organic'maNer'
–  Oceans'(water,'marine'sediments,'etc.)'
Short'Term'Carbon'Cycle'
Biosphere
CO2 Added by
Respiration
CO2 Removed
by PhotoSynthesis
Primary
Productivity
C
Photosynthesis: the conversion of carbon dioxide and water into
plant biomass using sunlight. Carbon flux from atmosphere to
organic carbon in vegetation.
Carbon Dioxide + Water + Sunlight = Sugar+ Oxygen
Respiration: Release of carbon from plant biomass into atmospheric
carbon dioxide (opposite of photosynthesis, accelerated by enzymes)
Carbon'Cycle'
Net'primary'producFvity'–'amount/rate'at'which'biomass'
accumulates'in'an'ecosystem.'''
Darker green = more productive (carbon in biosphere)
White = non-productive environment (little carbon)
Seasonal CO2 Variations
Why the
funny zig-zag
in the graph?
From Mauna Loa, Hawaii :Keeling Curve
Carbon'Dioxide'FerFlizaFon'
As'CO2'levels'increase,'plants'photosynthesize'faster'
Biosphere'increases'CO2'absorpFon'from'atmosphere'
Atmospheric'CO2'declines'
NegaFve'Feedback:'Stabilizes'Climate'System'
Limited'by'temperature'and'precipitaFon'constraints''
–  Forests'won’t'grow'outside'of'temp/precip'values'
Tipping'Points'For'Feedback'
Growth rate – CO2 absorbed
• 
• 
• 
• 
• 
Mean Temperature
Plants$Need$CO2,'But…'
Secondary'Fate'of'VegetaFon'
When'plants'decay,'some'carbon'is'
buried'and'stored'in'soils''
–  Anaerobic'decomposiFon'
(creates'CH4'and'CO2)'
–  May'be'exposed'by'erosion'
and'released'to'atmosphere'
–  May'be'buried'and'
incorporated'in'the'lithosphere'
(long'storage)'
–  Eroded'and'transported'by'
rivers'to'oceans'
CO2 Put Into
Atmosphere by
Decay
C
Organic Soil
Carbon
C
Biosphere'Carbon'DistribuFon'
Soil'Carbon'Storage'
Ocean'Carbon'Cycling'
Surface'Ocean'Reservoir'
Ocean<atmosphere'exchange'(fluxes)''
–  Flux'of'CO2'is'down<gradient'
Currently'Atm>Ocean,'so'Atm'"'Ocean'
–  Ocean'acts'as'buffer'system'
–  Have'absorbed'1/3'of'man<made'CO2'
emissions':'“Carbon$Sink”$
–  Solubility'of'Carbon'in'Ocean'' '
'inversely'proporFonal'to'temperature''
•  Warm'soda'analog'
–  Solubility'limited'by'Ocean'ph'(bio'uptake)'
CO2(g)
CO2(aq)
Oceanic'Carbon'Feedbacks'
Ocean'Carbon'Uptake'Feedback:'Air'temperature,'ocean'
temperature,'ocean'carbon'uptake,'atmospheric'CO2'
'
'
Oceanic'Carbon'Solubility'Feedback:'Air'temperature,'ocean'
temperature,'aqueous'solubility,'oceanic'CO2,'atmospheric'CO2'
' '*'biological'pump<pH'feedback'
' '*'mixed<layer'stability'(oceanic'convecFon)'
'
Atmospheric$CO2$
Ocean$Dissolved$
CO2$
Sea<Air'Carbon'Flux'
Air$
Temp$
Atm$
CO2$
Ocean$Temp$
Carbon$
Solubility$
Atmospheric$CO2$
Ocean$CO2$
Upper Ocean
Ocean$pH$
Biota$
Deep Ocean
Long-term Carbon Cycle
Sources
Outgassing from Earth's interior at ocean ridges, and volcanism
Sinks
Burial of deep sea sediments and undecayed biomass in soils + chemical weathering
Volcanic'ErupFon''
Can inject large amounts of CO2 into
the atmosphere, also sulfate aerosols
Limestone'(A'Carbonate'Rock)'
Granite: Silicate
Limestone: Carbonate
Most Carbon is ‘locked’ away in the earth’s crust (i.e. rocks) as
Carbonates (containing carbon)
Carbonates are formed by via silicates through the carbon cycle
In'Case'That'was'not'Clear'
Coke'='Rainwater '
'
'
'
'Menthos'='Silicate'Rock'
Silicate<to<Carbonate'Conversion'
Rain
2. Acid
Dissolves
Silicates
(carbonic
acid, removal
from atm)
1. CO2 Dissolves in
Rainwater
3. Dissolved Material Transported
to Oceans
4. CaCO3 Forms in
Ocean and Settles to
the Bottom
Calcium carbonate
Chemical$weathering$is$a$func@on$of$temperature$
1.  EvaporaFon'rate'increases'with'temperature'
2.  PrecipitaFon'rate'increases'with'evaporaFon'
3.  More'precipitaFon'means'more'weathering'
'
Draw'a'feedback'diagram'involving'the'following'components'
(a)  Temperature'
(b)  EvaporaFon'
(c)  PrecipitaFon'
(d)  Weathering'
(e)  Atmospheric'Carbon'Dioxide'
Plant'growth'modifies'feedback?'
'
Atmoapheric [CO2] (ppmv)
9
8
Emissions
7
6
5
4
3
2
1
0
4001850
380
1870
1890
1910
1930
1950
1970
1990
2010
[CO2]
360
340
320
2 ppm/year
300
280
0.81850
perature (deg C)
1.  Carbon'emissions'
exponenFally'increasing**'
2.  Atmospheric'CO2'increased'
100'ppm'in'last'150'years'
3.  Increased'GHG'Effect'
reflected'in'global'
temperatures'
'
Spring'2012:'397'ppm'
'
'
Fossil Fuel Emission (GtC/y)
Emissions,'ConcentraFons,'Temperatures'
0.6
0.4
0.2
0
-0.2
1870
1890
1910
1930
1950
1970
1990
Temperature
0.2 C/decade
2010
The'Rise'of'Atmospheric'Carbon'
Two$Primary$Culprits$
'
– Fossil'fuels''
•  Carbon'from'lithosphere'to'atmosphere'
– Land'use'change''
•  Carbon'from'Bio/soils'to'atmosphere'
Fossil'Fuels'
•  Fossil'fuels:'hydrocarbons'within'top'layer'of'Earth’s'crust'
•  Fossilized'remains'of'dead'plants'and'animals'exposed'to'heat/
pressure'of'Earth'for'thousands<millions'years'
•  World'derives'86%'of'energy'from'fossil'fuels'
•  Non<renewable'resource:'Using'up'organic<rich'sediments'faster'than'
they'accumulate'
Forests
Deforestation
in Progress
Agriculture
Deforesta@on:$Carbon$from$biosphere$into$atmosphere$
–  Forests$(sink)$replaced$by$agriculture$(source)$
–  Soil$disturbance$releases$soil$carbon$to$atmosphere$
–  Inhibits$amount$of$carbon$stored$in$biosphere$and$soils$
Historical Emissions from Land Use Change
Carbon Emissions from Tropical Deforestation
2000-2007
1.60
Africa
1.40
Latin America
1.20
S. & SE Asia
SUM
1.00
1.5 GtonC y-1
(16% total emissions)
0.80
0.60
0.40
0.20
R.A. Houghton, unpublished
2000
1990
1980
1970
1960
1950
1940
1930
1920
1910
1900
1890
1880
1870
1860
0.00
1850
Pg C yr-1
1.80
Other perturbations: Fire
US Wildfires release 4-6% of Fossil Fuel Emissions
Other perturbations: Ecosystem Disturbance
Insects
Drought Stress
Missing'Sink'
Sources
Fossil Fuel Combustion
Land Use Change
Sinks
Atmosphere
Oceans
Missing Sink
7.5 Gt C/yr
1.5 Gt C/yr
9 Gt C/yr
4.2 Gt C/yr
2.3 Gt C/yr
6.5 Gt C/yr
2.5 Gt C/yr
Hypotheses'for'Missing'Sink'
Ocean-Sediment Route
1.  Nutrification of coastal waters accelerates CO2 uptake,
then deposited to sediment and not found
2.  Fish
Biosphere
1.  Reforestation of previously deforested areas
2.  Enhanced plant growth (carbon-photo feedback)
3.  Tropical rainforests or Boreal Forests
Anthropogenic Sinks
Landfills, Carbon Capture & Sequestration
Fate of Anthropogenic CO2 Emissions (2000-2007)
1.5 Pg C y-1
4.2 Pg y-1
Atmosphere
46%
2.6 Pg y-1
Land
29%
+
7.5 Pg C y-1
2.3 Pg y-1
Oceans
26%
Canadell et al. 2007, PNAS (updated)
The'New'Carbon'Cycle'
Atmosphere now ~760
Not ALL anthropogenic carbon emitted to atm stays there
Drivers of Accelerating Atmospheric CO2
1970 – 1979: 1.3 ppm y-1
1980 – 1989: 1.6 ppm y1
1990 – 1999: 1.5 ppm y-1
2000 - 2007: 2.0 ppm y-1
To:
•  Economic growth
•  Carbon intensity
•  Efficiency of natural sinks
65% - Increased activity of the global economy
17% - Deterioration of the carbon intensity of the global economy
Carbon intensity = CO2 tons/GDP
18% - Decreased efficiency of natural sinks " Feedbacks
Canadell et al. 2007, PNAS
GT'Carbon'Equiv'
Carbon'dioxide'represents'¾'of'GHG'
emission'today'
Emissions'have'increased'70%'since'1970'
Heaviest'growth'due'to'transportaFon'
125%'
Demands'and'populaFon'growth'by'far'
offset'increases'in'energy'efficiency'
IPCC WG2 SPM Fig. 1.1
New'Geography:'Carbon'Emissions'
Per capita US emits 20 tons of CO2/per person
India emits 0.8 tons of CO2/ per person