The study looked at how economic growth, energy use, financial development, and CO2 emissions are connected in Portugal from 1971 to 2009. They found that economic growth and energy use lead to more CO2 emissions, while financial development reduces them. The researchers used different tests to show that these factors are linked in the long term. They also discovered that energy use and CO2 emissions affect each other in a feedback loop, and that economic growth and financial development influence CO2 emissions.