Abstract
We analyzed the magnitude, the trends and the uncertainties of fossil-fuel CO2 emissions in
the European Union 25 member states (hereafter EU-25), based on emission inventories from
energy-use statistics. The stability of emissions during the past decade at EU-25 scale masks
decreasing trends in some regions, offset by increasing trends elsewhere. In the recent 4 years,
the new Eastern EU-25 member states have experienced an increase in emissions, reversing
after a decade-long decreasing trend. Mediterranean and Nordic countries have also experienced
a strong acceleration in emissions. In Germany, France and United Kingdom, the
stability of emissions is due to the decrease in the industry sector, offset by an increase in the
transportation sector. When four different inventories models are compared, we show that the
between-models uncertainty is as large as 19% of the mean for EU-25, and even bigger for
individual countries. Accurate accounting for fossil CO2 emissions depends on a clear
understanding of system boundaries, i.e. emitting activities included in the accounting. We
found that the largest source of errors between inventories is the use of distinct systems
boundaries (e.g. counting or not bunker fuels, cement manufacturing, nonenergy products).
Once these inconsistencies are corrected, the between-models uncertainty can be reduced
down to 7% at EU-25 scale. The uncertainty of emissions at smaller spatial scales than the
country scale was analyzed by comparing two emission maps based upon distinct economic
and demographic activities. A number of spatial and temporal biases have been found among
the two maps, indicating a significant increase in uncertainties when increasing the resolution
at scales finer than 200 km. At 100km resolution, for example, the uncertainty of regional
emissions is estimated to be 60 gCm2 yr1, up to 50% of the mean. The uncertainty on
regional fossil-fuel CO2 fluxes to the atmosphere could be reduced by making accurate 14C
measurements in atmospheric CO2, and by combining them with transport models.