Global climate change is leading to decreased climatic predictability. Theoretical work indicates that changes in the climate’s intrinsic predictability will affect population dynamics and extinction, but experimental evidence is scarce. Here, we experimentally tested whether differences in intrinsic precipitation predictability affect population dynamics of the European common lizard (Zootoca vivipara) by simulating more (MP) and less predictable (LP) precipitation in 12 semi-natural populations over 3 years and measuring different vital rates. A seasonal age-structured matrix model was parametrized to assess treatment effects on vital rates and asymptotic population growth (λ). There was a non-significant trend for survival being higher in MP than LP precipitation, and no differences existed in reproductive rates. Small non-significant survival differences in adults explained changes in λ and survival differences among age-classes were in line with predictions from cohort resonance. As a result, λ was significantly higher in MP than LP. This experimentally shows that small effects have major consequences on λ, that forecasted decreases in intrinsic precipitation predictability are likely to exacerbate the current rate of population decline and extinction, and that stage-structured matrix models are required to unravel the aftermath of climate change.