Professor Rees explores the urgent need to substantially reduce our global CO2 emissions, or the atmospheric concentration will reach truly threatening levels. To do this, we need international cooperation, and global funding for clean and green technologies. He calls for the UK to keep one step ahead of other countries by developing technologies to reduce emissions, and says we should take the lead in wave and tidal energy, among other solutions. Science brings innovation but also risk, and random elements including fanatics can abuse new technologies to threaten our planet in ways we never dreamt of. The challenge, for our scientists, governments and people, is to confront the threats to our planet and find the solutions in science.