The Global Carbon CycleThe Global Carbon Cycle

Humans

Atmosphere

760 + 3/yr

Ocean

38,000

Land

2000

~90

~120

~120

7 GtC/yr

~90

About half the CO2 released by humans is absorbed by oceans and land

“Missing” carbon is hard to find among large natural fluxes

In a nutshellIn a nutshell

• About half of the CO2 emitted by human activities accumulates in the atmosphere

• The other half is absorbed by “sink” processes on land and in the oceans

• We lack a quantitative understanding of– Where the sinks are– How they work– How long they’ll keep working– Whether there’s anything we can do to

make them work better or for longer

Inverse Modeling of COInverse Modeling of CO22

Air Parcel Air Parcel

Air Parcel

Sources Sinks

wind wind

Sample Sample

Changes in CO2 in the air tell us about sources and sinks

Simulated Atmospheric CO2 in 1999

Atmospheric COAtmospheric CO22 Observations Observations ~2000~2000

Atmospheric COAtmospheric CO22 Observations Observations ~2006~2006

Orbiting Carbon ObservatoryOrbiting Carbon Observatory(Planned August 2007 launch)(Planned August 2007 launch)

• Global observations of fine-scale variations of column mean [CO2]

• Sunny days only

• Mid-day only

Scaling Studies Across Scaling Studies Across EcosystemsEcosystems

Mixed Temperate Forest• Northern Wisconsin (WLEF-TV)• 450 m tower, 5 years of fluxes• Radar soundings, aircraft sampling

Tropical Forest• Central Brazilian Amazon (LBA)• 3 sites: intact forest, logged, pasture• fluxes, in-situ data, aircraft sampling

Semi-arid Grass and Cropland• Oklahoma/Kansas border (ARM/CART)• 2 flux sites: C4 prairie and C3 wheat• Frequent soundings, PBL data

Process models evaluated locally against flux towers, aircraft data, and other field measurements, extrapolated using imagery

• Nocturnal respiration produces extremely high concentrations in morning stable layer

• Surface heating and TKE generation causes entrainment of lower-CO2 air from aloft

• Photosynthesis depletes CO2 in surface layer

• Buoyant plumes of low-CO2 air fill the convective boundary layer

Development of a CODevelopment of a CO22 “Mixed “Mixed Layer”Layer”

Coupled SiB-RAMS simulation

Denning et al, 2002

Possible Sources of Bias in New Possible Sources of Bias in New ObsObs

Surface carbon exchange (biology) covaries Surface carbon exchange (biology) covaries with meteorology on many time scales!with meteorology on many time scales!

• Diurnal cycle• Seasonal cycle• Cloud/clearsky bias

Unresolved atmospheric transport processes Unresolved atmospheric transport processes may significantly affect [COmay significantly affect [CO22] mixing ratio] mixing ratio

• PBL entrainment and diurnal pumping• Cumulus-scale updrafts and downdrafts• Frontal lifting

Orography, rainfall, soils, and Orography, rainfall, soils, and ecosystems are interactively ecosystems are interactively

organized at finer scales than can organized at finer scales than can be simulated in today’s global be simulated in today’s global

climate modelsclimate models

Land-Atmosphere Modeling in Land-Atmosphere Modeling in CMMAPCMMAP

• Current global climate models have a single atmospheric column above each land grid cell[Some (e.g., CCSM) now use non-spatially-explicit,

flux-weighted “tiles” of different land-surface types under each atmospheric column]

• Early MMF experiments reversed this structure: hundreds of atmospheric columns over a single land point

• Under MMAP, we will run hydrology, ecosystem physiology, and biogeochemistry at the cloud scale!

• Sampling problem: how will heterogeneity be specified to represent large areas?

• Photosynthetic efficiency is very Photosynthetic efficiency is very different for direct beam vs diffuse different for direct beam vs diffuse radiation … clouds change both total radiation … clouds change both total and partition of solar radiation … and partition of solar radiation … photosynthesis rates will respondphotosynthesis rates will respond

• What happens when rain falls on only What happens when rain falls on only part of the grid cell?part of the grid cell?

• Does hydrologic preconditioning in the Does hydrologic preconditioning in the land-surface help structure mesoscale land-surface help structure mesoscale organization of clouds and rainfall? organization of clouds and rainfall?

SummarySummary• By 2009, we will be swimming in hourly and

daily observations of atmospheric CO2 over terrestrial ecosystems

• Quantitative interpretation of the new data will be critically dependent on correct representation of cloud-scale transports and their interactions with ecosystems

• Under CMMAP, we will develop global simulations of the interactions among water, light, and ecosystems at the cloud scale

• CMMAP can make a huge contribution to Earth System science, way beyond clouds and the hydrologic cycle!