; (ii) in subparagraph (F), by striking the period at the end and inserting ; and ; and (iii) by adding at the end the following: (G) a Climate Choice Stock Index Fund as provided in paragraph (6). ; and (B) by adding at the end the following: (6) (A) The Board shall select an index which is a commonly recognized index comprised of common stock. (B) The historical performance of the index selected under subparagraph (A) shall be comparable to that of the other investment funds and options available under this subsection. (C) The Climate Choice Stock Index Fund shall be invested in a portfolio that is designed— (i) to replicate the performance of the index selected under subparagraph (A); (ii) such that, to the extent practicable, the percentage of the Climate Choice Stock Index Fund that is invested in each stock is the same as the percentage determined by dividing the aggregate market value of all shares of that stock by the aggregate market value of all shares of all stocks included in the index selected under subparagraph (A); and (iii) to ensure that no investment in the portfolio is an investment with respect to a fossil fuel entity. . (b) Effective date The amendments made by subsection (a) shall take effect— (1) only if the Federal Retirement Thrift Investment Board, in the report submitted under section 3(f)(2), indicates that the Board is unable to determine that it would be financially profitable, and consistent with the fiduciary duties of the Board, to implement low-carbon investment strategies; and (2) on the date on which the Board submits the report described in paragraph (1).