National Geographic: Deep ice sheets would cover much of the Northern Hemisphere thousands of years from now–if it weren’t for us pesky humans, a new study says. Emissions of greenhouse gases–such as the carbon dioxide, or CO2, that comes from power plants and cars–are heating the atmosphere to such an extent that the next ice age, predicted to be the deepest in millions of years, may be postponed indefinitely (quick guide to the greenhouse effect). “Climate skeptics could look at this and say, …