I didn't see your post, so don't take my comment as an indictment, but I see a lot of people spouting a lot of hateful, ignorant things with little to no understanding or self-awareness and then arguing against political correctness in defence when they're called out for it. Personally I find the image of Greta on the verge of a gang-bang offensive on multiple levels, but I believe everyone should have the right to express themselves. This isn't my platform however, and those running it have the right to decide what appears on it.
I will point out though that overpopulation is not the root cause of global warming, it's the excess of CO2 primarily from burning fossil fuels. Though of course there are many other contributing factors, flatulent livestock (not raised in rural Africa) well outstripping human output being one of them - if that's a concern, try cutting down on how much meat you consume. Overpopulation is not the concern we once thought it was, with ageing populations in first world countries and social advancements in poorer nations it's predicted that we'll stabilise at around 9 Billion, with a higher than 25% chance the population might actually begin to fall by 2100.