Current sea level rise is mostly the result of human-caused climate change: Warming temperatures melt ice and expand ocean water. But our planet is also feeling some effects of changes in the climate thousands of years ago. Over time, cyclical variations in Earth’s orbit have caused ice ages and great thaws, with glaciers covering much of North America and retreating as the planet warmed. These changes are different than the warming we’re experiencing right now, caused by human actions. Glaciers