From and after July 1, 2004, the board of supervisors of a county shall reduce the ad valorem taxes levied by the county in an amount equal to one-half (½) of the county’s share of the revenue derived from the oil and gas severance tax under Sections 27-25-505 and 27-25-705 as a result of offshore drilling on the Mississippi Gulf Coast. From and after July 1, 2004, the governing authorities of a municipality shall reduce the ad valorem taxes levied by the municipality in an amount equal to one-half (½) of the municipality’s share of the revenue derived from the oil and gas severance tax under Sections 27-25-505 and 27-25-705 as a result of offshore drilling on the Mississippi Gulf Coast.