1. Any retired member with fifteen or more years of creditable service at retirement receiving retirement benefits on August 28, 1997, shall receive on January first of each year, commencing on January 1, 1998, an increase in the amount of benefits received by the retired member pursuant to sections 169.410 to 169.540 during the preceding year of one hundred percent of the increase in the consumer price index calculated in the manner provided in this section; except that, no such increase in retirement benefits shall be paid for any year if such increase in the consumer price index is less than one percent. Such annual retirement benefit increase, however, shall not exceed three percent. A retired member qualified to receive an annual retirement benefit increase pursuant to this section shall not be eligible to receive an additional benefit until the January first after the first anniversary of the date on which he or she commenced receiving retirement benefits pursuant to sections 169.410 to 169.540. Benefits shall not be decreased in the case of a decrease in the consumer price index for any year.

2. For the purpose of this section, any increase in the consumer price index shall be determined by the board of trustees in November of each year based on the consumer price index for the twelve-month period ended on September thirtieth of such year over the consumer price index for the twelve-month period ended on September thirtieth of the year immediately prior thereto. Any increase so determined shall be applied by the board of trustees in calculating increases in retirement benefits that become payable pursuant to this section for the twelve-month period beginning on the January first immediately following such determination.

3. An annual increase in retirement benefits, if any, shall be payable monthly with monthly installments of other retirement benefits pursuant to sections 169.410 to 169.540.