> This concerns the “macroeconomic slide,” introduced as part of the 2004 reform of the public pension system. The macroeconomic slide is an indexing mechanism that automatically limits total payouts of retirement benefits to keep them in balance with revenue from contributions (supplemented by fiscal subsidies), even while the contribution rate of working people is held to a legal ceiling.

In other words, the pension system was designed as pay as you go. Pay as you go system doesn't do very well with a decreasing working population because it relies on the current working generation paying for the previous generation.