and procedures for the recycling of parts or disposal of such aircraft to ensure that such aircraft are taken out of service and not used to develop other aircraft with higher greenhouse gas emissions. (2) Exception Notwithstanding paragraph (1), in the case of an emergency declared by the Secretary or a national emergency declared by the President, the Secretary may temporarily waive the provisions of such paragraph that prevent the use of aircraft taken out of service pursuant to this section for the purposes of responding to such emergency or national emergency. (g) Authorization of appropriations There is authorized to carry out the program established under this section $1,000,000,000 and such sums shall remain available until expended. (h) Definitions In this section the following definitions apply: (1) Administrator The term Administrator means the Administrator of the Environmental Protection Agency. (2) Air carrier The term air carrier has the meaning given such term in section 40102 of title 49, United States Code. (3) Currently used aircraft The term currently used aircraft means— (A) aircraft in the bottom 25 percent of the air carrier’s aircraft fleet in terms of fuel efficiency per seat