Fires and Variability in the Global Carbon Cycle

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Fires and Variability in the Global Carbon
Cycle
Jim Randerson Department of Earth System
Science University of California Collaborators G
uido van der Werf, Jim Collatz, Louis Giglio,
Prasad Kasibhatla, Ruth DeFries, Doug Morton,
Eric Kasischke
NASA Joint Workshop on Biodiversity, Terrestrial
Ecology, and Related Applied Sciences August
24th, 2006
October 26, 2003 NASA Aqua MODIS true color
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Why is fire different from other terrestrial
carbon loss pathways?
Climate impacts of deforestation are amplified by
a suite of mechanisms tied to fire emissions
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How do fire emissions contribute to radiative
forcing of climate?
Red arrows represent a substantial RF
contribution from fire emissions
IPCC

• Fire influences climate via a series of forcing
  agents
• Relative importance of the forcing agents
  varies by biome

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How does the importance of fire as a carbon loss
pathway vary by biome?
Fire Rh Fire
Percentage of total carbon losses that were
returned to the atmosphere via fire emissions,
averaged over 19972004.
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Recent Advances in Our Understanding of Fire
Contributions to Carbon Cycle Variability

• Fire emissions and El Nino/La Nina
• A new active fire approach for detecting fires
  associated with tropical deforestation
• Peatland fires
• A hypothesis regarding human appropriation of
  interannual variation in CO2
• Feedbacks between carbon and climate - mediated
  by fire

This week in Science Westerling et al. Running
News Views
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Why does atmospheric CO2 increase at a faster
rate during El Nino?
El Nino events
IPCC
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Atmospheric CO Anomalies (Seasonal and
latitudinal trends removed)
Forward model estimate using satellite fire
observations Unique spatial-temporal CO
anomaly pattern for fires from each
region Satellite data allows for the
separation of tropical source regions in the
inversion
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Contribution of Fire to Global Atmospheric Trace
Gas Anomalies 1997 - 2001

• 2/3 of CO2 growth rate anomaly during 97/98 was
  caused by fire emissions
• Increased fire emissions occurred across
  multiple continents
• 1.3 Pg C in SE Asia
• 0.7 Pg C in South and Central Am.
• 0.2 Pg C in boreal forests of Eurasia and North
  America
• Fires can explain more than 100 of methane
  anomaly in NH in 97/98
• Direct CH4 emissions
• Indirect effects on OH via CO fluxes
• Drying is an immediate threat to terrestrial
  carbon stocks

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Spatial pattern of fire anomalies suggests a
large deforestation component
97/98 El Nino Emissions Anomalies
September 1997 - August 1998
Based on C3/C4 maps from C. Still
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Carbon 13 Isotope Data Also Supports a
Deforestation ComponentLangenfelds et al.
(2002)Randerson et al. (2005)
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Global burned area and fire emissions appear
largely decoupled from year to year
because emissions variability is controlled by
burning in forests (that burn more easily when
dry) whereas burned area is controlled by
fires in savannas, with more moisture leading
to denser fuels and greater fire spread rates
Southern Oscillation Index is a good predictor of
total global emissions (negatively correlated)
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A New Approach to Finding Deforestation Fires
Fire Persistence
The presence of repeated fire hot spots within a
1 km2 area during the fire season suggests that
the fires are burning substantial amounts of
fuels (e.g., wood). In the tropics these are
the areas humans are using fire to clear forests
Giglio et al. (2006)
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Multiple active fire observations during a fire
season within a 1 km2 radius are linked with
forest clearing in Matto Grosso
D. Morton and R. DeFries
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Quantifying fuel consumption in boreal and
tropical peatlands is critical for improving fire
emissions estimates
Turetsky et al. (2006)
Turetsky et al. (2004)

• The depth of burning in organic soils is an
  excellent metric for
• comparing models and observations

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Have humans co-opted the magnitude and sign of
the interannual CO2 response to ENSO?

• In intact moist tropical forest, a drying event
  may lead to net carbon uptake Saleska et al.,
  2003
• During El Nino, CO2 outgassing from the eastern
  tropical Pacific slows, leading to a sink anomaly
• Both of these natural processes generate a sink
  during El Nino, not a source

Unverifiable prediction During the Holocene, El
Nino caused atm. CO2 to decrease, the opposite
response from what is observed today Verifiable
prediction The sensitivity of CO2 to the SOI
will increase over the next century, because more
people will have the motive and opportunity to
burn forests when they dry out
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Fire feedbacks with climate not necessarily
positive!
Spring
CO2 and CH4 Aerosol O3 Albedo Net
Summer
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A combination of top-down and bottom-up
approaches required for the development of
accurate fire emissions time series
Kasibhatla et al.
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Future Directions (1)A New Era of Tropical
Biology from JPLs OCO
Launch in Fall 2008!
Combining MODIS, MOPITT, and OCO may allow us
to 1. Partition tropical CO2 fluxes into
deforestation and NEE components 2. Assess
interannual variability in deforestation fluxes
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Future Directions and Issues (2)

• Attribution of burned area and fire emissions to
  different classes of human activity, including
• Deforestation
• Pasture maintenance
• Agricultural waste burning
• Residual wildfire component
• Assess the relative importance of the different
  radiative forcing agents associated with fire for
  different biomes
• Integrate fire emissions with land cover change
  scenarios in coupled carbon climate model
  simulations to examine the impact of fire on
  carbon cycle feedbacks
• Fire emissions represent a key science
  deliverable provided by Terrestrial Ecology to
  other NASA Earth System focus areas
• 9 year time series from TRMM MODIS observations
• Improves our capability to interpret results from
  CO2 data assimilation systems

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Several Lines of Evidence Suggest that Rates of
Biomass Burning and Deforestation are Increasing
in South America
MODIS aerosol optical depth from Terra 1030am
equatorial crossing time
G.J. Collatz
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Fire Emissions Implicated During 97/98 El Nino
from Multiple Tracers
NOAA CMDL Trace Gas Anomalies
Langenfelds et al. (2002) CO2, H2, CO, CH4

and d13C covary,
implicating fires
Obs. Model
Almost all of fossil fuel emitted carbon
remained in the atmosphere during late 1997 and
early 1998 The carbon isotope ratio of the CO2
anomaly suggests a terrestrial source, and
specifically C3 plants Known emissions
ratios of CO2, CO, and CH4 from fires in savannas
and tropical forests link the trace gas anomalies
together
CO2 ppm/yr
d13C /yr
CH4 ppb/yr
CO ppb/yr
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Tropical Rain Monitoring Mission satellite fire
counts provide evidence for a migrating
deforestation front
Linear trend in fire counts from 1998-2005
Year of maximum detected fire counts
Van der Werf et al.
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Fire-Emitted Aerosols

• Net climate warming
• But cools the surface
• Deposition on snow and sea-ice increases SW
  absorption

Flanner and Zender
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Developing a metric of ecosystem fire
vulnerability using satellite fire counts and
precipitation data
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Tropical forests are more vulnerable to fire
during El Nino
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Global fires (1997-2004)
Van der Werf