Here is a documentary about Poland's smog problem and the country's efforts to tackle it, directed by Jonathan L. Ramsey and produced by Michał Konopa.

All around us are magic machines that suck carbon out of the air, cost very little and build themselves. Trees – in all their gorgeous variety and spectacular beauty – can make a massive difference to the world, if we accept one condition: we have to leave fossil fuels in the ground, where they belong.