Abstract
This paper asks a specific engineering question: is it physically feasible, using technology that already exists, to limit global warming to 2 °C and reach net-zero greenhouse gas emissions by 2070 — the outer boundary consistent with avoiding the most catastrophic climate tipping points? The answer, after examining energy, food, transport and the built environment, is: yes, but only under conditions that are currently far from being met. The window is narrow and closing. This paper sets out what those conditions are, why the financing objection does not hold, and why the precautionary principle demands we act as though the answer must be yes.