The Legislative Analyst's Office declared that the California State Teachers' Retirement System "may be the state's most difficult fiscal challenge" and suggested that tackling the shortfall is perhaps more important than other state debts.
The bulk of that additional money will likely have to come from taxpayers because investments and teacher contributions aren't enough.
The report was presented to lawmakers Wednesday during a hearing on ways to address the pension fund's unfunded liability.
If action isn't taken, the pension fund is expected to run out of money by 2044.
When combining the $4.5 billion with the current $1.4 billion annual contribution, the state would pay more for the pensions of retired K-12 teachers and community college instructors than it does for the entire University of California and California State University systems combined.
The report urged lawmakers to make changes soon because the fund's liability grows faster than other debts.