Global Linkages Between Vegetation, Atmospheric Composition and Climate

Fall AGU Meeting, San FranciscoDecember 19, 2008

Colette L. Heald

Acknowledgements:Dominick Spracklen, Russ Monson, Mick Wilkinson, Clement Alo, Guiling Wang, Alex

Guenther, Daven Henze, Larry Horowitz, Johannes Feddema, Jean-Francois Lamarque, Peter Hess, Francis Vitt, John Seinfeld, Allen Goldstein, Inez Fung

DISTURBANCE:Fires, beetles,

land use change

EMISSIONS:ParticlesOrganics

NOx…

+ oxidants

+ oxidation

O3

ANTHROPOGENIC INFLUENCE

↓ OH = ↑ CH4 lifetime

+ FEEDBACKS FROM CLIMATE CHANGE

(moisture, precipitation, T, hv)

?

PBAP

SOA

C5H8

FUTURE PREDICTION OF SECONDARY ORGANIC AEROSOLSources may be large(?), how MIGHT they change?

ZONAL MEAN SOA CONCENTRATIONS: 2100-2000

(ANTHROPOGENIC EMISSIONS):

POA (partitioning)Aromatics (precursor)

Trace gases (NOx, oxidants)

(BIOGENIC EMISSIONS):

BVOC (precursor)

(CLIMATE):Precipitation (lifetime)

T (partitioning, oxidation)Convection (distribution,

lifetime)Lightning (NOx aloft)Water vapour (POH)

(ANTHROPOGENIC LAND USE)

Climate impact is complex/compensatory/uncertain. Predict large increase in SOA burden (> 20%) tied to T-driven BVOC emissions,

with large sensitivity to future land use.

Global Model: NCAR CAM3-CLM3 (2x2.5)

[Heald et al., 2008]

METEOROLOGICAL AND PHENOLOGICAL VARIABLES CONTROLLING ISOPRENE EMISSION

LIGHTDiffuse and direct radiationInstantaneous and accumulated (24 hrs and 10 days)

TEMPERATURE (Leaf-level)instantaneous and accumulated (24 hrs, 10 days)

TPAR

L

T

[Guenther et al., 2006]SOIL MOISTURE suppressed under drought

AMOUNT OF VEGETATION Leaf area index (LAI)

Month

LAISUMMER

LEAF AGEMax emission = mature Zero emission = new

Eisoprene ≈ ECH4

ISOPRENE IN THE FUTURE

Isoprene emissions projected to increase substantially due to warmer climate and increasing vegetation density.

LARGE impact on oxidant chemistry and climate

2000 2100

NPP ↑ Temperature↑

Surface O3 ↑ 10-30 ppb [Sanderson et al., 2003]

Methane lifetime increases[Shindell et al., 2007] SOA burden ↑ > 20%

[Heald et al., 2008]

CO2 INHIBITION COMPENSATES FOR PREDICTED TEMPERATURE-DRIVEN INCREASE IN ISOPRENE EMISSION

CONCLUSION: Isoprene emission predicted to remain ~constantImportant implications for oxidative environment of the troposphere…

* With fixed vegetation

508 523

696

479Eis

op

(TgC

yr-1)

2000 2100 (A1B)

MEGANMEGAN with CO2 inhibition

Global Model: NCAR CAM3-CLM3 (2x2.5)

Empirical parameterization from plant studies

[Wilkinson et al., GCB, in press]

UNLESS…CO2 FERTILIZATION IS STRONG

CLM DGVM projects a 3x increase in LAI associated with NPP and a northward expansion of vegetation.

[Alo and Wang, 2008]

Isoprene emissions more than double! (1242 TgCyr-1)

BUT, recent work suggests that NPP increases may be

overestimated by 74% when neglecting the role of

nutrient limitation [Thornton et al., 2007]

[Heald et al., GCB, in press]

PRIMARY BIOLOGICAL AEROSOL PARTICLES (PBAP)

POLLEN

BACTERIA VIRUSES

FUNGUS

ALGAEPLANTDEBRIS

How much does this source contribute to fine-mode OC?

Jaenicke [2005] suggests may be as large a source as dust/sea salt (1000s Tg/yr)Elbert et al. [2007] suggest emission of fungal spores ~ 50 Tg/yr

LARGE particles (> 10 µm)

PRELIMINARY EMPIRICAL PBAP SIMULATIONElbert et al. [2007] identify that mannitol is a tracer for fungal spores

1 pg mannitol = 39 pg OM*

Global Model: GEOS-Chem (2x2.5)

Emission = constant[Elbert al., 2007] Emission = f(LAI, H2O)

A number of meteorological drivers could be expected to modulate fungal PBAP emissions. Here we find LAI and atmospheric water vapour concentrations are

the best predictors for observed average mannitol concentrations.

Test a series of meteorological drivers for mannitol emission.

BEST MATCH

PBAP OA (PM2.5) PBAP OA (PM2.5)

FUNGAL PBAP CONTRIBUTES <10% TO FINE-MODE OA SOURCE

Global Annual Emissions: 2003

66

30

POA SOA PBAPfine

PBAPcoarse

< 2.5 m 2.5-10 m

Tg

217

Global Model: GEOS-Chem (2x2.5)

Annual Mean Surface Concentrations

Consistent with AMS observations from AMAZE where OA concentrations were low.Need more PBAP observations!

[Heald and Spracklen, in prep]

CHALLENGES FOR UNDERSTANDING IMPACT OF VEGETATION ON COMPOSITION & CLIMATE AT THE GLOBAL SCALE

1. Land Use (Present/Future)

2. Species Diversity

3. Connecting scales:

SCALE UP?

HOW MUCH IS THERE???