A radical shift in engine technology in the 1970s (Honda's CVCC) drastically cut motor-vehicle emissions. A comparable game-changer could solve an even bigger pollution problem today.

Household air pollution from the traditional biomass-burning stoves used in many developing countries is the world's largest environmental-health threat, leading to 4 million premature deaths annually (S. S. Lim et al. Lancet 380, 2224–2260; 2012). We propose that a multimillion-dollar innovation prize should be set up, funded by governments or private philanthropy, to rapidly bring cleaner, more efficient and affordable stoves to poor people.

The competition would attract the world's best combustion scientists and engineers, and would help to take the current efforts of non-governmental organizations, small companies and academics to the next level (see S. Anenberg et al. Nature 490, 343; 2012).

The prize would be awarded for a durable, low-emission biomass-combustion unit — the 'heart of the hearth' — rather than for the stove itself. Stove designs could then be adapted around this to meet local requirements.