Advances in biotechnology, cybertechnology, robotics, and artificial intelligence, if pursued and applied wisely, could empower us to boost the developing and developed world and overcome the threats humanity faces on earth, from climate change to nuclear war. At the same time, further advances in space science will allow humans to explore the solar system and beyond. But there is no ‘Plan B’ for Earth – no viable alternative within reach if we do not care for our home planet. Lord Rees is Astronomer Royal.