The world population now, in 2021, is about 7.9 billion people. Use the following assumptions to estimate the current CO_2 levels. 7 billion the world population when this worksheet was created 390 ppm the CO_2 concentration when this worksheet was created 77 megatons - CO_2 emissions needed to raise the concentration by 1 ppm 1,150 megatons amount of CO_2 emitted annually per 1 billion population.