A 100,000 years ago, Homo sapiens lived only in Africa and nowhere else in the world. 25,000 years before, a group had left Africa but they did not survive. But human life in Africa remained under threat, and after what could have been a mega-drought of 40,000 years, our numbers were drastically reduced there too. Water levels in big lakes had dropped from almost 2400 feet to 400 feet, plant, animal life was devastated, and semi-deserts and scrub-land destroyed many of the food sources on which humans and other primates survived.
Scientists think this is why humans tried once again to leave Africa about 70,000 years ago. This time they succeeded, and all of us today are descendants of either those who left or those who survived in Africa during that time.
It is not clear how a significant climate change might effect us today. Partly because we don’t know how great the changes may be, or even altogether what they might be. But extreme weather events and flooding could merely be small harbingers of extreme danger. Without enough water, we cannot survive however technologically advanced we may be compared to our ancestors 100,000 years ago. Our oxygen supply could be depleted to mortal levels as a result of natural calamities like volcanoes or man-man catastrophes like massive unstoppable fires sweeping a continent or nuclear accidents that spread radiation around the entire globe.
The most dreadful outcome would be the total destruction of life; slightly less awful would be the survival of microscopic life forms, the kind that emerged during Earth’s first two billion years. Some assessments project the survival of as many as a billion humans. This sounds optimistic until you realize that means that six out of seven of living persons today would not survive an environmental meltdown.
It seems almost inevitable that global warming will result in more wars over, not the luxury of oil, but of water and food. Disease spreads more quickly in warmer climates too, so we are apt to be less enthusiastic about welcoming visitors to our home patch.
Maybe it would be easier to take global warming seriously right now.
The Big Bang to Now 