The following two things change everything:
1) Education of women and girls.
2) Human spaceflight.Education of Women and Girls
As noted by the Girl Effect
, and countless studies done in third world and developing nations, the education of women and girls goes a VERY long way to reducing poverty, overpopulation, disease, pollution, energy consumption, famine, war, and most of the world's woes. In fact, of all the solutions I can think of on this earth to making it a better place to live, this trumps them all, because everything else is birthed from this. Most environmental and peace movements were birthed because of well-educated women (or their sons).Human spaceflight
Our time on Earth is limited. No matter which way you look at it, whether an asteroid could strike in the next 50 years or the sun burns off the fragile parts of our magnetosphere and/or atmosphere in the next billion years, the Earth's days are numbered. Human spaceflight is critical to the survival of not just the human race, but to all species on Earth. One day, when we leave this planet, we will be the shepherds that will take the rest of the plants and animals with us.
The development of spaceflight capabilities is never too soon of an act. Some say we should learn to be peaceable before we learn to move to other worlds. We cannot afford to guess when that maybe-someday might be. A failure to develop spaceflight soon enough -- and again, we have no real way of knowing for sure when "soon enough" is -- could result in the annihilation not just of all humans and all history, but ALL known life. Failure means everything we and our ancestors have done will have been meaningless.
*Note: Both of these solutions must be done simultaneously. We cannot afford to focus on just one of them.