Practice 4　　The answer is, in a sense, all in our minds. For the last century, our society’s basic drive has been toward more—toward a bigger national economy, toward more stuff for each of us. And it’ s worked. Our economy is enormous; our houses are enormous. We are living large. All that more is created by using cheap energy and hence built on carbon dioxide (CO2)—which makes up 72% of all greenhouse gases.　　Some pollutants decrease as we get richer.  But carbon dioxide consistency tracks economic growth. As Harvard economist Friedman concluded last year, CO2 is “the one major environmental contaminant for which no study has ever found any indication of improvement as living standards rise.” This means that if we’re going to cope with global warming, we may also have to cope with the end of infinite economic expansion.　　That sounds gloomy, but maybe not. New data suggest that we’ve been overstating the issue for many decades. We made an assumption that more was better. It seemed a reasonable thinking. But in recent years, economists, sociologists and other researchers have begun to question that link. Indeed, they’re finding that at least since the 1950’s, more material prosperity has yielded little increase in humans’ satisfaction.