Nations should focus on lowering the cost of clean energy, not raising the cost of fossil energy. The goal? Make clean energy cheap enough to become a viable option for poor as well as rich nations. Until that happens, emissions will continue to rise, and no effort to regulate carbon can succeed. How do we accomplish that? Stop subsidizing old technology that will never compete with fossil fuels and create incentives for innovation. Along with ramping up support for research, governments should buy cutting-edge clean-energy technologies, prove them—and then give away the intellectual property, so others can improve on it.