water, perhaps... but that is about it...
We have more than enough oil and nat gas available to us, we have the ability to build more nuclear plants, we have an abundance of technology to continue improving our consumption efficiency, we continue to invest in R&D in cleaner alternatives.
That said, if there are endless resource wars, then we will not likely hit the 9 Billion level. Because fertility rates are dropping rapidly around the world as it is. An increase in death due to war would simply expedite the population peak timeline and its subsequent decline.