As Europe suffers another summer of record-breaking heatwaves, it is worth reflecting on the group perhaps least happy to benefit from the soaring temperatures – Green parties across the continent, which are, however, in a better electoral position than ever.

In May’s European parliament elections, the Greens won 22 more seats and 4.4% more of the vote than in 2014. Domestically, the German Greens participate in a majority of state governments and top national polling; the president of Austria is a Green-Independent and Greens have secured record vote shares in recent elections in Finland, Belgium and the Netherlands. They are also poised to pick up votes in forthcoming Swiss and Austrian elections. Although setbacks in Denmark and Sweden highlight the importance of national context, Greens have been gaining footholds outside their historical strongholds and are surging in polls in Ireland and the UK.

The most obvious explanation is found in shifting attitudes to the environment and the climate crisis. Although Europeans lost some belief in the threat during the 2000s, by 2016 large majorities across the continent agreed that global heating was happening, that it was at least partially caused by humans and that its impact would be negative. It is this “salience” that activates emotions and changes voting behaviour.

Britain's first climate assembly: can it help fix democracy too? Read more

In 2016, only 6% of EU citizens listed the environment as one of the two most important issues affecting their country. Just two years later, this figure had risen to 14% and is still climbing. In the latest Eurobarometer – a survey which monitors public opinion in every member state – 22% of Germans, 41% of Dutch and 39% of Swedes ranked “the environment, climate and energy” as one of their country’s top two most important issues. By contrast, southern and eastern Europeans remain fairly uninterested – just 1% of Greeks picked the issue in 2018, the same as in 2005. The UK ranks somewhere in the middle, at 11%, though this summer has seen a sharp increase.

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.

Play Video 1:35 'We cannot be radical enough': Attenborough on climate crisis action – video

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.

Although vote switching and electoral volatility have increased in Europe in recent decades, this is almost entirely within ideological blocs. Voters with broadly leftwing or rightwing predispositions now have multiple choices – with similar ideologies but differing priorities – at the ballot box.

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. It is no coincidence that the Green party of England and Wales (GPEW) could maintain its membership and a role in the party system after its 2015 “green surge” receded, whereas it quickly faded into irrelevance after its far larger 1989 European election vote share.

The case of the GPEW also highlights both how Green parties can take on different shapes according to national contexts, but also how long-term trends tend to see international party families converge ideologically in certain political conditions. Before 2016, the GPEW was a leftwing, anti-austerity protest party whose surge in many ways foreshadowed the rise of the old left of Jeremy Corbyn. But events since then have shaped it into a far more “European”, post-material Green party, swapping the previous flagship of anti-austerity for environmentalism and pro-Europeanism. This mirrors the previous convergence of far-right parties around their single policy flagship of opposition to immigration during the so-called refugee crisis, cleverly playing down any previous extremism or social authoritarianism.

What does all of this mean for parliamentary politics? In particular, how should the major losers of the Greens’ ascent – social democrats – respond? Leftwing parties have been tempted to focus on regaining an often sentimentalised vision of the “white working class”, almost always on the issue of immigration. This is a mistake. Across western Europe, most far-right, working-class voters were usually previously centre-right voters and their conservative value orientations mean their chance of voting for the centre-left are tiny.

Centre-left parties should focus on those who share their broad values, whether in terms of environmental quality, material opportunities or rights and freedoms. In the 1990s, social democrats were able to achieve electoral success after adopting the Greens’ environmental message en bloc, essentially halting the progress of Greens for two decades. Today, the demand for greater environmental action goes far beyond what centre-left parties are offering.

If western European social democratic parties want to regain offices of state, I’d suggest they offer ambitious proposals on the environment.

• James Dennison works at the European University Institute and is the author of The Greens in British Politics: Protest, Anti-Austerity and the Divided Left