Fires and Variability in the Global Carbon Cycle Jim Randerson Department of Earth System Science University of California Collaborators: Guido 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 24 th, 2006 October 26, 2003 NASA Aqua MODIS true color

Why is fire different from other terrestrial carbon loss pathways? Fire Climate impacts of deforestation are amplified by a suite of mechanisms tied to fire emissions

How do fire emissions contribute to radiative forcing of climate? Fire influences climate via a series of forcing agents Relative importance of the forcing agents varies by biome IPCC Red arrows represent a substantial RF contribution from fire emissions

How does the importance of fire as a carbon loss pathway vary by biome? Percentage of total carbon losses that were returned to the atmosphere via fire emissions, averaged over 1997–2004. = Fire R h + Fire + …

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 CO 2 Feedbacks between carbon and climate - mediated by fire This week in Science: Westerling et al. Running News & Views

IPCC El Nino events Why does atmospheric CO 2 increase at a faster rate during El Nino?

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

Contribution of Fire to Global Atmospheric Trace Gas Anomalies /3 of CO 2 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 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 CH 4 emissions - Indirect effects on OH via CO fluxes - Drying is an immediate threat to terrestrial carbon stocks

Spatial pattern of fire anomalies suggests a large deforestation component 97/98 El Nino Emissions Anomalies September August 1998 Based on C 3 /C 4 maps from C. Still

Carbon 13 Isotope Data Also Supports a Deforestation Component Langenfelds et al. (2002) Randerson et al. (2005)

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)

A New Approach to Finding Deforestation Fires: Fire Persistence The presence of repeated fire hot spots within a 1 km 2 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)

Multiple active fire observations during a fire season within a 1 km 2 radius are linked with forest clearing in Matto Grosso D. Morton and R. DeFries

Turetsky et al. (2004) Turetsky et al. (2006) Quantifying fuel consumption in boreal and tropical peatlands is critical for improving fire emissions estimates The depth of burning in organic soils is an excellent metric for comparing models and observations

Have humans co-opted the magnitude and sign of the interannual CO 2 response to ENSO? SOI CO 2 growth rate – 2040 El Nino La Nina In intact moist tropical forest, a drying event may lead to net carbon uptake [Saleska et al., 2003] During El Nino, CO 2 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. CO 2 to decrease, the opposite response from what is observed today Verifiable prediction: The sensitivity of CO 2 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

Fire feedbacks with climate not necessarily positive! Spring Summer CO 2 and CH 4 Aerosol & O 3 Albedo Net

Kasibhatla et al. A combination of top-down and bottom-up approaches required for the development of accurate fire emissions time series

Future Directions (1) A New Era of Tropical Biology from JPL’s O=C=O Launch in Fall 2008! Combining MODIS, MOPITT, and OCO may allow us to: 1. Partition tropical CO 2 fluxes into deforestation and NEE components 2. Assess interannual variability in deforestation fluxes

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 CO 2 data assimilation systems

Several Lines of Evidence Suggest that Rates of Biomass Burning and Deforestation are Increasing in South America MODIS aerosol optical depth from Terra 10:30am equatorial crossing time G.J. Collatz

 13 C ‰/yr CH 4 ppb/yr CO ppb/yr NOAA CMDL Trace Gas Anomalies Langenfelds et al. (2002): CO 2, H 2, CO, CH 4 and  13 C covary, implicating fires CO 2 ppm/yr Almost all of fossil fuel emitted carbon remained in the atmosphere during late 1997 and early 1998 The carbon isotope ratio of the CO 2 anomaly suggests a terrestrial source, and specifically C3 plants Known emissions ratios of CO 2, CO, and CH 4 from fires in savannas and tropical forests link the trace gas anomalies together Fire Emissions Implicated During 97/98 El Nino from Multiple Tracers Obs. Model

Tropical Rain Monitoring Mission satellite fire counts provide evidence for a migrating deforestation front Linear trend in fire counts from Year of maximum detected fire counts Van der Werf et al.

Fire-Emitted Aerosols Net climate warming But cools the surface Deposition on snow and sea-ice increases SW absorption Flanner and Zender

Developing a metric of ecosystem fire vulnerability using satellite fire counts and precipitation data

Tropical forests are more vulnerable to fire during El Nino

Global fires ( ) Van der Werf