The importance of shifting to a green economy is clearly established within the UN Social Development Goal (SDG) 13. SDG 13 focuses on combating climate change and its impacts; the UN reports that over 197 parties have signed the UN document. However, the green economy definition is so broad that it encompasses all 17 SDGs. A feasible approach in this paper is to limit our discussion to CO2, which accounts for almost 75% of greenhouse gases. Methane, nitrous oxide (NOx), and fluorinated gases account for 14%, 8%, and 1% respectively. Thus, we use world data from the World Development Indicators to examine the main sources of CO2 from 1960 to 2014. We find the persistence of CO2 over the years, which indicates that most countries have failed to limit the output of CO2 and other greenhouse gases. The conclusions drawn are stronger within an econometric model relating CO2 to GDP by employing an Environmental Kuznets (EKC) model for each region of the world. NOx emissions are also discussed later in the paper as another application of the EKC model.