These arguments have merit but must be measured against the reality of carbon growth. Consider China: Its carbon emissions increased by an average 8.6% a year between 2002 and 2012. Were China to continue at this pace for 27 years until it reaches today’s U.S. GDP per capita, it would emit 99 gigatons of carbon in 2041 alone, or three times the world’s current emissions.

This scenario is too pessimistic. As countries develop, they become more efficient in energy use. But even if China tapered its emissions growth from 8.6% to zero over the same 27 years, it would still emit as much carbon in 2041 as the entire world does today. And that’s not including emissions growth from India, Africa and South America.

Is there any hope of limiting carbon emissions to 30-50 gigatons in 2030, as many climatologists have called for, with substantial reductions thereafter? Some countries, notably Denmark and Sweden, have significantly reduced emissions. Can the U.S. do the same?