... As we have learned, these gases form an invisible barrier that, like a greenhouse's glass ceiling, keeps reflected heat of the sun from escaping our atmosphere. The denser that gaseous barrier grows, the hotter things get and the faster glaciers melt. As they flow off the land, we are warned, seas rise. Yet something else is lately worrying geologists: the likelihood that the Earth's crust, relieved of so much formidable weight of ice borne for many thousands of years, has begun to stretch and rebound.