As energy systems transform to rely on renewable energy and electrification to mitigate climate change, they encounter stronger year-to-year variability in energy supply and demand. Yet, most infrastructure planning relies on a single weather year, risking a potential lack of robustness. In this paper, we optimize capacity layouts for a European energy system under net-zero CO₂ emissions for 62 different weather years. Subsequently, we fix the layouts and optimize their operation in every other weather year to assess resource adequacy and CO₂ emissions. Our analysis shows a variation of ± 10% in total system costs across weather years. Layouts designed for years with compound weather events prove more robust, achieving resource adequacy of 99.9% and net-negative CO₂ emissions of −0.5% per year relative to 1990 levels. CO₂-emitting backup generation regulated by a CO₂ tax offers a cost-effective measure to enhance robustness. It increases emissions only marginally, keeping average emissions below 1% of 1990 levels over all layouts. Our findings underscore the need for policymakers and energy stakeholders to account for interannual weather variability in future infrastructure planning.