ab = {{12654.53`, 17297.85`}, {12105.26`, 15729.26`}, {11320.35`,
15037.48`}, {10390.35`, 13446.09`}, {9366.78`,
12827.8`}, {8065.08`, 9152.64`}, {7081.47`, 8411.`}, {6229.18`,
7387.86`}, {5514.84`, 6712.4`}, {4517.04`, 5421.54`}, {3649.81`,
4334.37`}, {3310.32`, 3778.57`}, {2785.8`, 3159.57`}, {2179.46`,
2553.34`}, {1807.2`, 2289.07`}, {1418.51`, 1852.95`}, {1315.52`,
1695.63`}, {1201.61`, 1521.08`}, {1160.51`, 1321.33`}};

ab1 = MapThread[Prepend, {ab, Table[2000 + i, {i, 1, 19}]}]

ab1 = ({Table[2000 + i, {i, 1, 19}]}~
Join~(ab\[Transpose]))\[Transpose]

ab1 = Table[{2000 + i, ab[[i, 1]], ab[[i, 2]]}, {i, 1, 19}]

ab1 = MapIndexed[({
#2 + 2000, #
1} // Flatten) &, ab, {1}]