At long last countries are waking up to the dangers of carbon-dioxide pollution and a finite supply of fossil fuel. The bad news is that emergent green technology risks spawning new trade wars. A firestorm of public criticism emerged in the United States last year, with reports of taxpayer stimulus funds being used to buy 240 Chinese-made turbines for a new wind farm in west Texas. The world’s pursuit of low-carbon sources of energy collided with the national need to create jobs.