Economic growth once meant more greenhouse gas emissions – more factories, more demand for electricity, more workers able to afford cars – but more than 20 countries found ways to expand their economies between 2000 and 2014 even as they reduced their heat-trapping carbon emissions.

Denmark, Ukraine and Hungary achieved the sharpest drops in carbon dioxide, reducing their emissions by 30, 29 and 24 percent, respectively, as their economies grew by 8, 49 and 29 percent.

The U.S. has managed to grow its economy and also reduce its heat-trapping carbon emissions. Courtesy World Resources Institute

The U.S. cut its CO2 emissions by 6 percent as its economy expanded by more than a quarter.

Worldwide, greenhouse gas emissions plateaued in 2014 and 2015 while global economic activity increased.

The methods varied by country: Nations like Sweden, for example, introduced taxes that encouraged switching to cleaner sources of energy like solar and wind. Denmark rapidly expanded renewable energy sources.

Oil and gas groups like the American Petroleum Institute contend that the U.S. fracking boom has also been instrumental in reducing emission. Huge quantities of cheap, cleaner-burning natural gas, they argue, gave electric utilities an economic incentive to switch away from coal, the world's largest source of greenhouse gas emissions.

The World Resources Institute, a global research nonprofit that supports environmental protection and actions to slow climate change, presented the results in a blog post Tuesday. The organization drew its data from the International Energy Agency, an independent analysis group of 29 nations, as well as the World Bank and BP.

