Slavery. Organized crime. Corruption of governments. Imperialism. Economic inequality. Nuclear proliferation. The coming waves of climate refugees. Insufficient water. The coming crop failures in about a decade that will kill 1/4 of the world's population.
Peak oil. Everybody stopped talking about it in the late 00s when it was discovered that shale wasn't inaccessible after all, but now every shale patch except the Permian has already peaked and the first derivative of the Permian output is plummeting.
All of them.<p>One of the things that exacerbates the others is not just the lingering effects of superstition, but its growth rate which can still sometimes outpace the rate of civilization.
The greatest technical ones are:<p>- Countering aging / human rejuvenation.<p>- Atmospheric carbon capture and utilization.<p>- Strong materials / bringing materials up to their theoretical strengths. (The theoretical strength of fiberglass is ~40GPa; the best samples generally measure at ~5GPa.)<p>Yet it's the non-technical challenges surrounding governance, how to handle social media, how to deal with falling birthrates, etc., that are much more pressing.