British playwright Duncan Macmillan is what you might call a theatrical illusionist; with the most unassuming and economic resources, he tames huge existential questions, or put another way, he takes the big and overwhelming and transfigures it into the small and engaging. Macmillan’s taut and brilliantly pertinent two-hander, Lungs, is one of these magic tricks, conjuring a philosophical examination of man’s impact on the planet out of a shopping trip to Ikea.

A couple, two Gen-Y thirty-somethings (Kate Atkinson and Bert LaBonté), are queuing for flat-pack furniture when they stumble into an age-old conversation: whether or not to have children. The question may be an ancient one, but in our present-day world of global warming and rising sea levels, the decision to bring another human being into the world (along with their 10,000 tonne carbon footprint) becomes twisted by a moral dilemma: if you’re a good and ethically conscious person, aware of the unstoppable man-made destruction of the Earth, is it right to have a child?

Of course, a worthy tome about the inconvenient truth would make for an off-puttingly preachy evening, but Macmillan’s superb knack for capturing effortlessly natural dialogue frames Lungs’ ecological subtext in a...