I tend to agree with this (but I admit that I haven't given it much thought). For the most part, population growth is far higher in developing countries. As some of the other commenters here point out, population growth tends to slow down as your country gets richer. However, the issue is that the environmental impact of people in rich countries is far higher per capita.

Some back of the napkin math:

- India population = 1,324,171,354 [0]

- India growth rate = 1.19% [0]

- India CO2 metric tons per capita = 1.58 [1]

Assuming each additional person has the same per capita carbon footprint:

1,324,171,354 * 1.0119 * 1.58 = 2,117,087,809 additional tons CO2/year

Compare to the United States:

- US population = 328,863,150 [2]

- US growth rate = 0.62% [2]

- US CO2 metric tons per capita = 15.53 [1]

328,863,150 * 1.0062 * 15.53 = 5,138,909,636 additional tons CO2/year

So even though the US has 1/4 the population and a lower growth rate, the growth of carbon footprint is 2.5 times higher. These numbers are obviously very inexact, but the point is that if you believe that the current rate of CO2 output is unsustainable (and this is hard to dispute), then even if the world population levels off, this is likely due to increased prosperity. And increased prosperity means more consumption per capita and more consumption means more carbon footprint (and other environmental damage).

[0] https://en.wikipedia.org/wiki/Demographics_of_India

[1] https://www.ucsusa.org/global-warming/science-and-impacts/sc...

[2] https://en.wikipedia.org/wiki/Demography_of_the_United_State...