The European Commission has determined that airlines will have 212,892,052 metric tons of carbon dioxide available to them in 2012 and 208,502,525 metric tons from 2013 as aviation is included in the European Union’s emissions trading system (ETS).

The data were derived after a careful analysis of historical aviation emissions. In establishing the rules for airlines being included in the ETS, the European Union was looking at average emissions between 2004 and 2006, using Eurocontrol data. The emissions (and allowances) cover all airlines operating within the EU, as well those flying into or departing the region. U.S. carriers have launched a legal challenge to their inclusion in the ETS.

As has been the case with other elements of trying to integrate airlines in the ETS, the release of the latest set of information comes much later than planned. The commission says that it conducted additional studies “to increase the accuracy of the estimations of historic aviation emissions, in particular in relation to the fuel used by auxiliary power units (APU). Together with the support from Eurocontrol and contribution from [the] aviation sector, a methodology to assess the APU was developed and the fuel consultation by APU was estimated. This figure was then added to the flight-based CO2 emissions.”

Several more steps are required, though, before the system fully takes effect. In announcing the allocation levels, the commission also says that later this year, it will “formally determine the amounts of emission allowances to be auctioned, to be distributed free of charge to aircraft operators and to be allocated to a special reserve for new entrants.”

The EU plans to give away 82% of allowances, with 15% auctioned off and the rest reserved for new entrants or other cases.

Member states manage the allocation, with foreign carriers allocated to different EU states (in most cases to the U.K. regulator). The EU rules state that revenue from auctioned allowances should go to combat the effects of climate change, but are not required to go to aviation-related activities.

One of the concerns for some European carriers has been that the effects of air space shutdown last year due to volcanic ash could skew the allowance allocation. But the EC says, “We have not seen data to suggest that the impact of the ash cloud will have a material impact on the distribution of free allowances between aircraft operators.” However, it adds, “redistribution might occur if certain airlines had to cancel a greater proportion of flights than others, while the vast majority of operators have been impacted by the flight restrictions resulting from the volcanic ash cloud. Indeed, all the estimations that we have seen confirm that distributional impacts are very small.”

Moving away from 2010 as the benchmark year would require a two-year legislative process the EC is rejecting.

The EU ETS directive says that member states should use all auction revenues from aviation allowances to tackle climate change, including in the transport sector, and to adapt to the effects of climate change.