In February 2013, the International Civil Aviation Organization’s environmental committee finalized a CO2 certification requirement to serve as the basis for a global CO2 (efficiency) standard for new aircraft.
Under the requirement, the CO2 intensity of new aircraft will be evaluated at three steady-state cruise test points, with aircraft required to meet efficiency targets set as a function of their maximum takeoff mass (MTOM) after correcting for the floor area of the aircraft. This approach is expected to rank the CO2 intensity of new commercial aircraft in proportion to emissions per seat kilometer flown, can be used to set a standard via a single continuous line, and should be inexpensive for manufacturers to certify as it is patterned on existing data gathering practices. Disadvantages of the procedure include its failure to measure non-cruise fuel burn, the use of flight conditions unrepresentative of day-to-day operations, providing no direct crediting for lightweight materials, and uncertainty about whether some future technologies to reduce fuel burn will be accurately characterized under the procedure.
For additional detail, see the full update here.