Are Green parties becoming more popular?

Reports of the European elections have included comment on the increasing success of the Green Party.
the European Parliament has a live election page where you can see the results by group #
and results by country

Are green Parties becoming more popular?
The ESRC party membership project recorded a surge in membership in Britain., between October 2014 and May 2015, it  increased from less than 20,000 to over 60,000. The MAPP Project has been examining and comparing party membership in European nations from 1990-2012. It has visualisations of who belongs
For recent uk polls on voting intentions and attitudes towards green parties see the what the UK thinks website EU which has voters opinions on policies of different parties towards Brexit

Who votes green and why do they?
this recent article from EUROPP Blog discusses when Green Parties are successful
it has some useful graphs on the spread of green parties since the 1980s. It is based on a full text journal article. they conclude: The findings show that 'voter demand, institutions and mainstream party strategy all affect the Green vote. Green parties do well in societies with post-materialist conflicts caused by high levels of wealth or the presence of a tangible environmental dispute'
Another useful article on this topic is
Brendan Prendiville, « The Green Party: ‘Green Surge’ or Work in Progress? », Revue Française de Civilisation Britannique [Online], XX-3 | 2015, Online since 01 December 2015, connection on 27 May 2019. URL : http://journals.openedition.org/rfcb/618 ; DOI : 10.4000/rfcb.618

which has charts on party membership and who voted focussing on elections 2010-2015

For more information on political parties try this specialist PSA Group which has a mailing list and regular updates on academic study of political parties.