A 49 percent spike in unfunded pension promises could drive up taxpayer contributions to Sonoma County government pensions by $13.6 million over the next three years.

Three years after a highly controversial rollback in retiree medical benefits, Sonoma County government’s costs for retiree health care and its long-term liabilities again are on the rise. The increase is shown in a county report made public last week and headed to the county Board of Supervisors Tuesday for acceptance.

In 2002, at the urging of labor and with the endorsement of management, the county Board of Supervisors approved a more generous set of pension benefits for all current workers. The change, fueled by salary increases and combined with other workforce trends, is now seen as driving the upward spiral in pension costs.