The terms "carbon intensity" and "emissions intensity" are also sometimes used.[106] Emission intensities may be calculated using market exchange rates (MER) or purchasing power parity (PPP).[2]: 96 Calculations based on MER show large differences in intensities between developed and developing countries, whereas calculations based on PPP show smaller differences. According to a study discussing the relationship between urbanization and carbon emissions, urbanization is becoming a huge player in the global carbon cycle. Depending on total carbon emissions done by a city that hasn't invested in carbon efficiency or improved resource management, the global carbon cycle is projected to reach 75% of the world population by 2030.[107]