Human beings are a cancer on the Earth. The Western US is drying, cracking, and sinking due to over-use of water. There's a gyre of plastic garbage twice the size of Texas in the Pacific ocean. Staple foods such as corn, wheat, and rice have been genetically modified to the extent that their biodiversity is the lowest it's ever been, making crops intended to feed billions in danger of being wiped out by just one new insect, disease, or bacteria. We're injecting noxious chemicals into the ground to extract more oil to burn which is adding to the biggest problem, climate change. And there is Fukushima Daiichi and the potential for the destruction of life in the entire Pacific ocean and possibly half of the planet - an environmental catastrophe so unthinkable that in all of science fiction (afaik) no one has ever thought of it.
All the schemes to support even more people - new farming technology, more water pipelines, cleaner energy - tout that they can keep up with impossible predictions of doubling or tripling the population but ignore that we're pretty much at the limit right now. The only way we can stop eating away at the Earth is to stop growing and that's not going to happen. Scientists might think we'll hit 11 billion by 2100, but I think an Armageddon is very likely to occur before we do.