The US and China are major polluters, that’s because they are major economies, which means they are major energy consumers. There’s a balancing act between the economy and energy. If no one used energy there’d be no economy (effectively, and given today’s technology); so, cutting back on energy to cut back on pollution also could mean cutting back on the economy and jobs. But, the correlation is not as simple because each country uses energy more or less efficiently. One measure is the amount of energy (BTUs) it takes to generate economic activity ($). By that measure, islands and extreme environments are far less efficient. By that same measure, the US is reasonably efficient, not because it has more efficient energy but partly because it’s institutions and industry are more efficient – ranking 58th.
(Click on the map for the link.)