How can we tell? The quick answer is that the good stuff has gotten much cheaper. Emissions free wind and solar are increasingly cost competitive with coal and now make up the major ity of the u.s.'s new power generating capacity. LED lighting has reached a tipping point, and other energy saving technologies programmable thermostats, superefficient windows are going mainstream. Battery prices are plunging which is why electric vehicle sales are doubling every year, while traditional vehicles guzzle less gasoline. And government policies President Obama's new carbon rules, carbon taxes in Sweden and British Columbia, cap and trade regimes in California and the E.U. are making dirty energy more expensive, accelerating the transition to cleaner alternatives.