Abstract
We estimatethenorthernhemisphere(NH)terrestrialcarbon
sink bycomparingfourrecentatmosphericinversionswith
land-based Caccountingdataforsixlargenorthernregions.
The meanNHterrestrialCO2 sink fromtheinversionmodelsis
1.7 PgCyear1 over theperiod2000–2004. Theuncertaintyof
this estimateisbasedonthetypicalindividual(1-sigma)
precision ofoneinversion(0.9PgCyear1) andisconsistent
with themin–max rangeofthefourinversionmeanestimates
(0.8 PgCyear1). Inversionsagreewithintheiruncertaintyfor
the distributionoftheNHsinkofCO2 in longitude,withRussia
being thelargestsink.Theland-basedaccountingestimateof
NH carbonsinkis1.7PgCyear1 for thesumofthesixregions
studied. The1-sigmauncertaintyoftheland-basedestimate
(0.3 PgCyear1) issmallerthanthatofatmosphericinversions,
but noindependentland-basedfluxestimateisavailableto
derive a‘betweenaccountingmodel’uncertainty.
Encouragingly, thetop-downatmosphericandthebottom-up
land-based methodsconvergetoconsistentmeanestimates
within theirrespectiveerrors,increasingtheconfidenceinthe
overall budget.Theseresultsalsoconfirmthecontinuedcritical
role ofNHterrestrialecosystemsinslowingdownthe
atmospheric accumulationofanthropogenicCO2