Tough climate: Deputy Liberal leader Ted O’Brien, Opposition Leader Sussan Ley and Nationals leader David Littleproud. “In our lifetime, emissions have to go to zero,” the activist is quoted as saying. “That’s a message people understand.”When the slogan was coined, “in our lifetime” seemed a lifetime away. Given the average “life sentence” imposed in the Australian court system is about 13 years, it would have been several lifetimes away when first uttered. Now it’s just a couple of lifetimes away, questions are becoming more urgent about how net zero can be achieved.