Transcript NCAR/UCAR Overview Visit of Jeff Nesbit September 13, 2006

Closing
in edit
on the
Missing
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titleCarbon
style
Sink: Implications for Climate
and
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textMitigation
styles
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List of Nominations
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Dr. Britton Stephens
National Center for Atmospheric Research
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Outline:
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1. Current state of scientific knowledge
concerning global carbon cycling
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Secondchange
level mitigation challenges
2. –
Climate
associated
with knowledge gaps
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3. New northern
» Fifthand
level tropical land uptake
estimates from airborne CO2
measurements
4. Implications of new results for
strategies to address climate change
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Careful atmospheric CO2 measurements since the
1950s show that about half of fossil fuel emissions
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remain
in theto
atmosphere
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FF
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Atm
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» Fifth level
[IPCC, 2007]
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How can we separate the natural uptake
between
ocean?
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[Sabine et al, Science, 2004]
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Annual fluxes are small relative to balanced
seasonal exchanges and to standing pools
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andMaster
flows
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Annual residuals
Net Oceanic
Sink
Land-Based
Sink
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The global carbon cycle for the 1990s, showing the main annual
fluxes in GtC yr –1. [IPCC, 2007]
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Carbon Units
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1 Petagram C (PgC) = 1 Gigaton C (GtC) =
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“1 Billon
Tons
C” = 3.7 Gigaton CO2 (GtCO2)
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level
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–C
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C2H6O
CH4
CO2
H2CO3
CaCO3
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Uncertainties on natural ocean and land fluxes
are +/- 25 to 75 %
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1990s
2000-2005
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± 0.1Master4.1text
± 0.1 styles
Atmospheric
Increase
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Fossil Fuel
Emissions
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Ocean-to-
6.4 ± 0.4
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Atmosphere
Land-toAtmosphere
–2.2 ± 0.4
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level
» Fifth level
–1.0 ± 0.6
Net Oceanic
Sink
Land-Based
Sink
7.2 ± 0.3
–2.2 ± 0.5
–0.9 ± 0.6
Land-use
Change 1.6 (0.5 to 2.7)
1.5*
Residual
Land Sink -2.6 (–4.3 to –0.9)
-2.4*
[IPCC, 2007 and *Canadell et al., PNAS 2007]
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Global atmospheric inverse models and surface
data have been used to make regional flux
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estimates
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Forward: Flux + Transport = [CO2]
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Inverse: [CO2] – Transport = Flux
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12 Model Results from the TransCom 3 Study
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List of Nominations
Model
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Model Name
1
CSU
2
GCTM
3
UCB
4
UCI
5
JMA
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MATCH.CCM3
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MATCH.NCEP
8
MATCH.MACCM2
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NIES
A
NIRE
B
TM2
C
TM3
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Systematic trade
off between
northern and
tropical land
fluxes
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Regional
flux uncertainties
are very
large
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•• All
modeltoaverage
and standard
deviations:
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Northern Land = -2.4 ± 1.1 PgCyr-1
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Tropical Land = +1.8 ± 1.7 PgCyr-1
• At $30/ton of CO2:
± 1.5 PgCyr-1 = ± $165 Billion
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Challenges associated with flux uncertainty
1) Verification
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Challenges associated with flux uncertainty
2) Prediction
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How much can we burn?
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[IPCC, 2007]
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Challenges associated with flux uncertainty
3) Detection
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Thermohaline circulation
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Melting permafrost
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• All model average and standard deviations:
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-1
Northern Land = -2.4 ± 1.1 PgCyr
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level= +1.8 ± 1.7 PgCyr-1
Tropical
Land
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Bottom-up estimates
have generally failed
to find large uptake in
northern ecosystems
and large net sources
in the
• tropics
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An helpful discovery about the nature of the
model disagreements
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Land and
Northern
Land fluxes
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plotted versus vertical CO gradient
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List of Nominations
Model
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Model Name
1
CSU
2
GCTM
3
UCB
4
UCI
5
JMA
6
MATCH.CCM3
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MATCH.NCEP
8
MATCH.MACCM2
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NIES
A
NIRE
B
TM2
C
TM3
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Systematic trade
off is related to
vertical mixing
biases in the
models
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12 Airborne Sampling Programs from
Laboratories
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Northern Hemisphere sites include Briggsdale, Colorado, USA (CAR); Estevan
Point, British Columbia, Canada (ESP); Molokai Island, Hawaii, USA (HAA); Harvard
Forest, Massachusetts, USA (HFM); Park Falls, Wisconsin, USA (LEF); Poker Flat,
Alaska, USA (PFA); Orleans, France (ORL); Sendai/Fukuoka, Japan (SEN); Surgut,
Russia (SUR); and Zotino, Russia (ZOT). Southern Hemisphere sites include
Rarotonga, Cook Islands (RTA) and Bass Strait/Cape Grim, Australia (AIA).
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12 Airborne Sampling Programs from
Laboratories
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Vertical CO2 profiles for different seasonal intervals
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Comparing the Observed and Modeled Gradients
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• 3 models that most
Northern Land
closely reproduce the
observed annual-mean
Tropical
Land (4,
vertical
CO2 gradients
5, and C):
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Northern Land
=
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-1
Name
-1.5 ± 0.6 Model
PgCyr
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Model
1
CSU
2
GCTM
level
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-1
Tropical
Land
=
3
UCB
+0.14 ± 0.8 PgCyr
UCI
Most of the
models
overestimate the
annual-mean
vertical CO2
gradient
• All model average:
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JMA
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MATCH.CCM3
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MATCH.NCEP
Northern
Land =
8
MATCH.MACCM2
-1
-2.4 9± 1.1 PgCyr
NIES
A
NIRE
Tropical
Land
=
B
TM2
-1
+1.8C ± 1.7 PgCyr
TM3
Observed value
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Airborne CO2 measurements indicate:
•Northern forests, including U.S. and
Europe, are taking up much less CO2 than
previously thought
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•Intact tropical forests are strong carbon
sinks and are playing a major role in
offsetting carbon emissions
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[Stephens et al., Science, 2007]
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Outcomes of this work:
•Helps to resolve a major environmental
mystery of the past two decades
 Northern “missing carbon sink” may not
have been found because it is not there
•Improved understanding of processes
responsible for carbon uptake will improve
predictions of climate
change and assessment
of mitigation strategies
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Implications for Climate Mitigation Strategies
1) National
emission
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Temperate
North America
Tropical
America
Fan et al, 1998
-1.4 ± 0.5
NA
Transcom 3, 2004
-0.9 ± 0.4
+0.7 ± 1.1
-0.5 ± 0.25
NA
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U.S. SOCCR
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NOAA CarbonTracker
» Fifth level -0.5 ± 0.6
0.0 ± 0.7
[PgCyr-1]
Models 4, 5, and C still estimate a strong sink in
Temperate North America (-0.9) and a strong source in
Tropical America (+0.8) but with large compensating
flux revisions in other regions. Zonal partitioning by
these models is highly uncertain.
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Implications for Climate Mitigation Strategies
2) Processes
prediction
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a. Northern uptake will slow as forests mature
b. A tropical
sink styles
will continue as
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long as CO2 continues to increase
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c.
A tropical
climate change sink may decrease
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evenlevel
reverse depending on feedbacks
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Implications for Climate Mitigation Strategies
3) Deforestation
releases
C pooltitle
and
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removes C sink
Nominal C Pool
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text styles
(tC/hectare)
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Boreal Forest
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Temperate Forest
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Tropical Forest
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35
60
120
(~ 200 w/peat)
style
Sink spread evenly
over all forest
(tC/hectare/year)
1
2
A palm oil plantation can only offset fossil
CO2 emissions at ~ 3 tC/hectare/year
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Implications for Climate Mitigation Strategies
4) Caveat
short-termtitle
naturestyle
of
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afforestation and reforestation offsets
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[IPCC, 2007]
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On century time-scale oceanic and
geologic sequestration will be required
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Conclusions
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1) Large uncertainties exist in estimates of regional
carbon fluxes and limit our ability to make optimal
mitigation decisions
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2) There is a strong need for expanded atmospheric
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and
oceaniclevel
observational networks related to
carbon
cycling
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level
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level suggest that tropical forests are
3) Airborne
CO2 data
Fifth
level and northern much less carbon
taking up a»lot
more
than previously believed
4) Preventing tropical deforestation is important for
preserving existing carbon pools and the
capacity to absorb future CO2 emissions
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