... Why is the salience of the environment soaring? Historically, some academics have played down the effects of “real-world” events or citizens’ abilities to deduce which issues matter, instead emphasising strategic manipulation of the agenda by the media and politicians. While these certainly count, the salience of the environment, like that of most other issues, ultimately does reflect real events. Evidence of soaring temperatures is becoming the lived reality of citizens, making scientific findings on the resultant collapse of ecosystems increasingly difficult to ignore.

However, there is more to the current Green success than greater environmental concern. The geographical disparities can still be partially explained by the long-term emergence of “post-material values” in affluent western European societies in the 1970s. These saw individuals move beyond materialist, redistributive concerns to quality-of-life matters, including care for the environment.

Moreover, the breakdown of postwar western European party systems and the accompanying decline in class voting mean that we are increasingly inclined to vote according to psychological predispositions and less because of social group. Without these social anchors in place, mainstream parties have become more vulnerable to “anti-incumbency” voting and single-issue voting, primarily to new parties. Centre-right parties have had to deal with challenger, anti-immigration parties, while the centre-left has suffered at the hands of, first, anti-austerity parties and, increasingly, environmentalist parties...

... All of these challenger parties, including the Greens, have displayed a remarkably more professional appearance to voters, mirrored by far more effective internal machinery, all of which has been aided by the arrival of the internet and social media...

https://www.theguardian.com/commentisfree/2019/jul/28/europe-greens-on-fire-and-not-just-because-of-sweltering-heat