(1) The legislature finds and declares that many cities operating under prior plans have excess and unfunded liabilities, and the liabilities cannot be amortized by the percentage contributions set forth in this chapter.
(2) The board shall, within 6 months after a city is granted membership in the retirement system, determine the excess and unfunded liability of the city's previous plan. If the board determines that the city has an excess and unfunded liability under a previous plan that is not funded by sums on deposit or funds available for deposit in the pension trust fund, the city shall pay an additional sum over a period of time to amortize the city's excess liability.