When a political issue rises to the top of the public agenda, it puts pressure on decision-makers, shifts power to actors engaging with the issue, and opens a window of opportunity. This article shows that online mass media contributed to the rapid rise of climate change on European public agendas in and around 2019. It also suggests that climate issue publics, that is particularly concerned and interested citizens, were influenced most. Conversely, citizens without strong climate opinions are not subject to influence from intensive media coverage. The results come from vector autoregression (VAR) models that take advantage of unique daily salience time series. The time series are constructed from weekly repeated nationally representative surveys of the public (N = 25,445) and online news articles (N = 6,905) by a dominant mass media news outlet that boasts a particularly large, trustful, and diverse audience. Traditional mass media can retain a powerful agenda-setting role even in increasingly fragmented media environments. But the target of their influence depends on the issue and the composition of corresponding issue publics, plausibly due in part to individual differences in use and processing of information about the issue.