TABLE 4.1 Reducing Uncertainties in CO2 Emissions Through New Atmospheric and Ocean Observations

 

Decadal Global

Annual Global

Annual Regional

Annual Continental

Annual National

Method

Net Flux to the Atmosphere

Net Flux to the Atmosphere

Fossil Fuel

IPCC LUCF

Land-ocean Sink Partition

Tropical Biosphere Changes

Mid-latitude Biosphere Changes

Fossil Fuel

IPCC LUCF

Fossil Fuel

IPCC LUCF

Current uncertainties

 

 

 

 

 

 

 

 

 

 

 

State of art, including 13CO2, O2, oceanic, and atmospheric data

1a

(1%)

1a

(7%)

2b

(25%)

5b

3b,c,e

3c,f

3c,d,f

5

5

5

5

Potential improvements

 

 

 

 

 

 

 

 

 

 

 

State of art plus 14CO2

 

 

1-2

5b

2g

2g

2g

2g

5

2-4

5

All of the above plus intensive aircraft observations

 

 

 

 

 

 

 

++g

 

++g

 

All of the above plus intensive ocean observations

 

 

 

 

++g

(+)g

(+)g

(+)g

 

 

 

All of the above plus other tracers of combustion (e.g., CO, NOx, HCN)

 

 

 

 

 

 

 

++

 

++

 

All of the above plus satellite CO2 observationsh

 

 

 

 

++

++

++

++

 

++

 

NOTES: IPCC = Intergovernmental Panel on Climate Change; LUCF = land-use change and forestry. Other than %, units are Pg of CO2 per year for the 2000 decade.

1 = <10% uncertainty; 2 = 10-25%; 3 = 25-50%; 4 = 50-100%; 5 = >100% (i.e., cannot be certain if it is a source or sink).

Potential improvements: ++ = likely and direct; (+) = indirect in the sense that it would directly improve estimates of ocean fluxes which, in a tracer-transport inversion, would reduce errors for land masses, especially for those at similar latitude.

a2σ uncertainty of annual increase, P. Tans, <www.esrl.noaa.gov/gmd/ccgg/trends/>.

bDenman et al. (2007).

cConway et al. (1994); Ciais et al. (1995).

dPeters et al. (2007).

eGruber et al. (2009).

fTans et al. (1990); Gurney et al. (2002).

gImprove transport in models—expert judgment of committee.

hIf systematic errors of satellite CO2 retrievals can be mastered through ongoing comparisons with in situ chemical measurements, frequent resampling can lead to the small errors of annual averages that are required for flux estimates.

oceanic data only to within 25 percent. The reason for the difference is the large interannual variation in the size of sources and sinks in the terrestrial biosphere and oceans, which must be separated from the total atmospheric increase to estimate the contribution from fossil fuel. Uncertainty in the anthropogenic emissions from land-use change and forestry is greater than 100 percent because both anthropogenic and natural changes in the terrestrial biosphere have almost identical effects on atmospheric CO2, 13C, and O2. For this reason, the inventory and remote sensing methods described in the previous chapters are needed for the a priori data on emissions from land use and forestry.

Because of transport uncertainty and the lack of measurements over much of the globe, estimates of the total net flux of CO2 from broad bands of latitude on a seasonal time scale are uncertain by at best 25-49 percent, compared to only 7 percent for the globe (Table 4.1). The situation is far worse for estimates of continental or national emissions (>100 percent) because east-west air flow rapidly mixes emissions signals and makes inversions sensitive to model error. In addition, there remains the question of whether the amplitude of the greenhouse gas perturbations caused by national emissions is large enough to detect with in situ networks or satellites.



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