Mike Gardiner seems ignorant of the fact that sea ice is, you know, floating. When it melts the sea doesn’t rise. However, less sea ice means that the oceans reflect less sunlight.
Meanwhile Dan Story purports to know the average global temperature during the Ordovician (488–443 million years ago.) But he has a problem with the term “average.” During the Ordovician, the sun was smaller and sent less energy to the earth. And most of the earth’s land mass was centered at the South Pole. So there’s that.
But the big caveat to his “average” is that the guesstimated 4500 ppm (not 5000) of CO2 did not exist at the same time as the Ordovician ice age. This has been known since 2005. https://researchnews.osu.edu/archive/earlyice.htm
So, Dan’s “average temperature” for a 45 million year period of earth’s history really doesn’t mean anything.