Recent rapid changes in climate and environmental conditions have significantly impacted coastal ecosystem functioning. However, the complex interplay between global and local effects makes it challenging to pinpoint the primary drivers. In a multi‐ecosystem study, we analyzed pluri‐decadal trends of bivalve‐δ13C as recorder of global environmental changes. These trends were correlated with large‐scale natural and anthropogenic climate proxies to identify whether coastal biota responded to global effects. Our findings revealed decreasing bivalve‐δ13C trends in all sea regions, mainly linked with increased temperature and atmospheric‐CO2 concentrations, the later generating a decrease in atmospheric‐CO2 δ13C values (Suess effect) because of fossil‐fuel burning. After removing the Suess effect from bivalve‐δ13C trends, ongoing global climate variability continues to affect most ecosystems, possibly intensified by combined, interacting regional or local effects. These results highlight the need to consider large‐scale effects to fully understand ecosystem and food web responses to the multiple effects of global change.