NASA Carbon Cycle

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Active Sensing of CO2 Emissions over Nights,
Days, Seasons (ASCENDS)
Berrien Moore IIIClimate Central Princeton,
NJ University of New Hampshire
NASA Carbon Cycle Ecosystems Joint Science
Workshop 28 April - 2 May 2008
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Active Sensing of CO2 Emissionsover Nights,
Days, and Seasons (ASCENDS)Launch
2013-2016Mission Size Medium
ASCENDS provides a highly precise global dataset
for atmospheric CO2 column measurements without
seasonal, latitudinal, or diurnal bias. This
will quantify the regional carbon sources/sinks
and thereby increase understanding of the
underlying mechanisms are central to prediction
of future levels of CO2.
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Orbiting Carbon Observatory - JPL
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Anthropogenic C Emissions Fossil Fuel
2006 Fossil Fuel 8.4 Pg C
2006-Total Anthrop. Emissions 8.41.5 9.9 Pg
1850
1870
1890
1910
1930
1950
1970
1990
2010
1990 - 1999 1.3 y-1 2000 - 2006 3.3 y-1
Raupach et al. 2007, PNAS Canadell et al 2007,
PNAS
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Trajectory of Global Fossil Fuel Emissions
50-year constant growth rates to 2050 B1
1.1, A1B 1.7, A2 1.8 A1FI 2.4
Observed 2000-2006 3.3
Raupach et al. 2007, PNAS Canadell et al 2007,
PNAS
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The Airborne Fraction (2000-2006)
45 of all CO2 emissions accumulated in the
atmosphere
The Airborne Fraction
The fraction of the annual anthropogenic
emissions that remains in the atmosphere
55 were removed by natural sinks
Ocean removes 24
Land removes 30
Canadell et a.l, 2007, PNAS
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Atmospheric CO2 Concentration
Year 2006 Atmospheric CO2 concentration 381
ppm 35 above pre-industrial
1970 1979 1.3 ppm y-1 1980 1989 1.6 ppm
y1 1990 1999 1.5 ppm y-1
2000 - 2006 1.9 ppm y-1
NOAA 2007, Canadell et al., 2007, PNAS
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Attribution of Recent Acceleration of Atmospheric
CO2
1970 1979 1.3 ppm y-1 1980 1989 1.6 ppm
y1 1990 1999 1.5 ppm y-1

• To
• Economic growth
• Carbon intensity
• Efficiency of natural sinks

2000 - 2006 1.9 ppm y-1
65 - Increased activity of the global economy
17 - Increased carbon intensity of the global
economy
18 - Decreased efficiency of natural sinks
Canadell et al., 2007, PNAS
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Impact of Stabilizing Emissions versus Sabilizing
Concentrations of CO2
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Global Carbon Sources and Sinks
Source GCTE / IGBP
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Science Questions

• How is the Earth's carbon cycle changing? What
  are the spatial and temporal patterns of exchange
  of CO2 between the atmosphere and the surface,
  and how are these patterns affected by large
  scale modes in weather-climate, and how are these
  patterns affected by human actions? What are the
  feedbacks of climate on the carbon cycle, and
  what are the likely effects on the carbon cycle
  of these feedbacks in the future?
• This mission will make measurements day and night
  at all latitudes in all seasons of total column
  mixing ratio of CO2 with sufficient precision to
  allow accurate determination of spatial and
  temporal pattern of the sources and sinks of CO2.
• The CARBON CYCLE. Carbon in the atmosphere is a
  controlling factor on climate and hence on
  ecological productivity and the sustainability of
  life.

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Challenges Posed by the Science Questions

• Because of spatial and temporal variability,
  practical determination of the pattern of sources
  and sinks from surface measurements is
  impossible. The only viable approach is to infer
  aspects of the rates of exchange by inverting the
  causal relation between source-sinks and
  atmospheric concentration.

• This requires measurements of total column CO2
  with high precision measurements in all seasons
  and all latitudes with a focus upon mid to lower
  troposphere, under a varying set of large-scale
  weather-climate modes.

MODIS
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Importance of the Science Questions

• The largest uncertainties about the Earths
  carbon budget are in its terrestrial components
  land biosphere is the most vulnerable carbon pool.

Global Carbon Budget (IPCC, 2007)
ASCENDS will reduce major uncertainties and help
explain the missing carbon sink and its
dynamics.
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Importance of the Science Questions

• Large uncertainties remain about the size of the
  oceanic sink. Recent evidence suggests that the
  Southern Ocean sink may be saturating. Oceanic
  uptake of CO2 increases the acidity of the ocean
  with unknown ecological effects.

ASCENDS will resolve the geographical and
temporal patterns of oceanic sources and sinks.
Global Carbon Budget (IPCC, 2007)
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Science Rationale Science Measurement
Requirements

• ASCENDS CO2 Measurement Requirements derived from
  Observing System Simulation Experiments (OSSEs)
  conducted by Peter Rayner and Frédéric
  Chevallier, CEA-CNRS.
• Assumed measurement precision for 100-km
  tropospheric CO2 column measurement over land of
  1.3 ppmv during day and 0.8 ppmv at night and
  over water of 4.2 ppmv during day and 2.1 during
  night.

ASCENDS will make major contribution to knowledge
of CO2 sources sinks.
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Active Sensing of CO2 Emissions over Nights,
Days, Seasons (ASCENDS)
Mission Objectives
Airborne Demonstration
Day/Night Global CO2 Column Measurements
Airborne Test Flights

• Approach
• ASCENDS will deliver laser based remote sensing
  measurements of CO2 mixing ratios (XCO2)
• Day and night
• At all latitudes
• During all seasons
• ASCENDS includes simultaneous measurements of
• CO2 number density (ND) tropospheric column
• O2 ND column surface pressure for CO2 to XCO2
• Temperature profile improved CO2 accuracy
• Altimetry surface elevation, cloud top heights
• CO profile identify combustion sources of CO2
• ASCENDS will be a logical extension of OCO and
  GOSAT capabilities

• Summary
• ASCENDS identified as a medium size mission in
  the NRC Decadal Survey
• LRD 2013-2016 to overlap with OCO (OCO scheduled
  launch Dec 2008)
• Data have been collected from airborne
  instruments to verify the CO2 measurement
  capability of the laser based approach

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Payload
CO2 column mixing ratio (XCO2) measurement with
Laser Absorption Spectrometer (LAS) technique
requires the simultaneous measurement of the CO2
column number density (CND) the O2 column number
density to converting the CND to XCO2 and the
path length of the measurement. A temperature
profile measurement is also required to constrain
the XCO2 measurement. A column CO measurement
over the same XCO2 path is also recommended for
interpreting sources and sinks of CO2.

• CO2 column measurement
• CO2 Laser Absorption Spectrometer to resolve (or
  weight) the CO2 altitude distribution,
  particularly across the mid to lower troposphere.
• 1.6 µm LAS only baseline
• Integrated 1.6 µm 2.0 µm
• Surface pressure measurement
• O2 Laser Absorption Spectrometer to convert CO2
  number density to mixing ratio.
• Surface/cloud top altimeter
• Laser altimeter to measure CO2 column length.
• Temperature sounder
• Six channel passive radiometer to provide
  temperature corrections.
• CO sensor
• Gas Filter Correlation Radiometers (at 2.3 4.6
  µm) to separate biogenetic fluxes from biomass
  burning and fossil fuel combustion.
• Imager
• To provide cloud clearing for soundings.

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Key Mission Milestones

• Pre-Phase A Present April 2010
• Start Phase A April 2010
• Confirmation April 2012
• Payload Delivery April 2014
• Satellite Ship September 2015
• Launch October 2015
• End of Primary Mission (3 years) October 2018
• Note Earlier launch (August 2014) is
  technically feasible if prior year
  implementation funding is provided.

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