The North American continent is covered by an ice sheet that ends just south of the border between what were once the United States and Canada, to where the human city of Chicago once stood. The central region of North America is cold and dry. The atmospheric temperature is so low (and drops to freezing during the night) that the air has little capacity for holding moisture. What was once the most productive agricultural land on the planet is now little more than a vast, barren dust bowl.
Along the eastern edge of the continent, the Atlantic Ocean has receded, leaving a broad coastal plain coastal plain topped by the Appalachian Mountains. Inland, there is an unending expanse of cold sand and cracked rock. The North American Desert is as bitterly cold as the Gobi Desert was in East Asia. It stretches for about 1,500 miles (2,400 kilometers) until it finally fetches up against the rocky barrier formed by the glacier-ridden Rocky Mountains away to the west.
All year long, piercing winds moving 100 kilometers an hour sweep southwards from the ice, stirring up vicious sandstorms and scouring away any potentially productive pockets of soil. Occasionally, winds howl in from the coastal regions, but very little rain reaches the interior. What precipitation there is tends to be snow, but even this falls infrequently. Any snow cover on higher ground is thin and patchy. There is a significant difference in temperature between the Equator and the edge of the icecap, producing a steep temperature gradient from north to south. This leads to unstable conditions with screaming tornadoes ripping across the interior far more frequently than they did during previous times.
Vegetation is sparse in this harsh, arid landscape. Only the hardiest of plants exist, but in small numbers. Indeed, very little life can survive above ground. Those animals able to live in this bleak desert must withstand freezing temperatures and protect themselves from the violent storms. The animal inhabitants of the North American Desert are supreme specialists, brilliantly adapted to cope with the specific demands of an uncompromising habitat. Some species have adapted physically, whilst others have altered their living environment. Animals that live here need to last out times when food is in short supply. In order to do so, they have developed remarkable strategies for storing energy and conserving food. Some animals have even developed altruistic feeding habits, sharing food with other colony members to ensure the survival of the species as a whole.