I am an active proponent and co-organizer of double conferences, a new eco-friendly conference format whose purpose is to reduce long-distance travel while still fostering long-distance interactions. Events take place in two different locations connected by live video stream.
We have co-organized two double conferences, with a third on the way.
If you might be interested in running a double conference, please feel free to get in touch with me.
The first double conference was held in August 2018, entitled Higher algebra and mathematical physics and co-hosted by the Perimeter Institute for Mathematical Physics (Waterloo, Canada) and the Max Planck Institute for Mathematics (Bonn, Germany); you can see the conference websites here and here. You can read a write-up of our experience organizing this event on page 32 of this issue of the London Mathematical Society newsletter.
The second double conference was held in June 2020, entitled Geometric representation theory and co-hosted by the same two institutions; you can see the conference websites here and here. However, due to the global pandemic, it was moved entirely online. Ben Webster (one of the co-organizers) wrote a succinct summary of the lessons we learned regarding online conferences, which you can read as a tweetstorm here.
A third double conference is currently in the works, to be held in summer 2022 and to be entitled Homotopy theory with applications to arithmetic and geometry.