When continental ice sheets reached their maximum extent during the last glacial period, they locked up roughly 6 million cubic miles of ocean water. That volume had to come from somewhere, and the evidence shows it came directly from the world's oceans. Sea level dropped at least 400 feet, with some estimates placing it closer to 450. That's not a theoretical model, that's what the geomorphology and coastal evidence tell us.
Today there's concern about sea level rising a foot or two over the next century. That's worth monitoring. But context matters. At the end of the last ice age, as those ice sheets collapsed and returned their water to the oceans, sea level rose more than 400 feet. That's not speculation, that's what happened. Understanding the scale of natural variability in Earth's climate system isn't about dismissing current concerns. It's about grounding those concerns in the full scope of what this planet is capable of.