@SW-User We are in an Ice Age. This is a long period of oscillating temperatures about a mean that is relatively cool over the Earth's life so far, and marked by terrestrial ice cover in high latitudes and on high mountains.
If Nature had been allowed it own way, the temperature would still be rising but very much more slowly than mankind is now forcing it; probably slowly enough for us to adapt over many centuries although it would bring sea-levels possibly a few tens of metres higher than now. The tropics would be much hotter.
If the Ice Age continues the temperature would slowly fall again to introduce a new glacial phase. In NW Europe, ice-sheets extended about as far South as the latitude of the River Thames, South of that was a wide band of Arctic Tundra and the English Channel was occupied by a major river valley.
Each major phase lasts many tens of thousands of years.
If the Ice Age is in fact ending, the eventual result would be vast arid areas, far higher sea-level and little or no high-latitude or high-altitude ice.
We can not control fully-Natural climate oscillations, just as we cannot control earthquakes (different causes, of course). We can though avoid what we are doing - artificially accelerating them.
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Could humanity survive another full interglacial, in perhaps another 10 000 years time? Lots of presently-low-lying land would be under the sea so everyone would have to move inland to higher ground; bringing considerable pressure on land, agriculture and other resources.
Can humanity survive another glacial phase? Well, it has done. Early Man lived through it, simply staying in the more equitable latitudes although apparently venturing Northwards into the tundra. The sea-levels would be considerably lower than now, leaving all our present harbours high-and-dry inland. The high latitudes would be uninhabitable, forcing huge numbers of people to move to warmer regions.
Crucially though, it was far easier for our ancestors twenty thousand years ago than it ever could be now. There were far, far fewer people on Earth, their societies and ways of life were far, far simpler than ours now; and it was relatively easy for them to move about and adapt as conditions changed over many generations.
