Hans-Josef Fell just announced a referendum in Berlin with the goal of enacting a law requiring climate neutrality until 2030.
In contrast to the federal level, Berlin has a system of referendum since 2006. There have been three successful initiatives in the last decade, two of them concerning airports and the other one privatization of the water infrastructure. See the relevant Wikipedia article for more information.
Fell is one of five representatives of this initiative. It is supported by a broad coalition of organizations interested in more effective climate policy.
A previous step in the process of the referendum already resulted in over 30,000 signatures, clearing the hurdle as the first such project under corona conditions.
I support the general idea and would sign as well, if I still lived in Berlin.