Global net zero emissions is what it will take to halt global warming. Net zero is possible, affordable, and the alternatives are, quite literally, unthinkable. So, the only real question is when, not whether, we will achieve it. This series sets out the case for achieving net zero as soon as possible to limit the damage to our weather, the natural world and human societies. It will argue that the greatest risks of delay are not the direct impacts of climate change that everyone tends to focus on, but geopolitical instability arising from increasingly evident injustices or panic-stricken measures like solar geo-engineering. Finally, we must talk about when net zero for individual countries: while the rich have a duty to move fastest, everyone benefits from an inclusive transition.