Behavior change — shutting off the lights, turning off the air conditioner — is useful, but not even in the ballpark of responding to this need. Neither are the subsidies that governments provide to renewables such as solar and wind power. The cost of meeting future energy requirements with existing green technologies would be “beyond astronomical,” Gates has argued.

There was no way to get to the moon by stacking ladders. That required an entirely different technology. Current environmental responses are the stacking of ladders. “We need breakthroughs,” says Gates.

It is sobering when your only sufficient policy response is the production of a miracle. But I’ll add a few more depressing political and economic factors. Human beings are fairly good at calculating costs into their decision-making — saving for a rainy day, buying car insurance — if the time horizon is a few months or a few years. They are not as good at assuming burdens, as in environmental policy, when the time horizon is a few decades or centuries. And they are terrible at shouldering burdens when future costs are paid disproportionately by other people — in this case by people living in poor countries that are more vulnerable to coastal flooding or drought.