Spam limits require that I not make it easy to locate the book – google “John O Robertson Climate” if you’re curious.
There is no normal, merely periods of stasis and periods of change. Lots of alternating from iceball five or six hundred millions of years ago (rescued from that by titanic vulcanism in what is today Siberia) to warm at both poles. We may be headed back toward the warm end of things – and we may see a new era of ice age when lack of Arctic ice shuts down the Arctic-North Atlantic Conveyor – – – meaning that the Gulf Stream no longer warms Northern Europe. Ewwwwps.
Humans are the ultimate in flexibility, so by the time the sun’s perimeter expands all the way out to earth’s orbit several billion years from now, we may have found a way to terraform not just Mars but move Earth farther from the fire. Who can tell?