June 11, 2008—Satellite images from 1972 (left) and 2007 (right) show water-level decline in Lake Chad, once the world's sixth largest.

At the junction of Nigeria, Niger, Chad, and Cameroon, the lake is now one-tenth its former size, due to declining rainfall and diversion of water for human use.

The images are part of Africa: Atlas of Our Changing Environment, a new UN book unveiled today to illustrate how climate change is affecting the continent.

"It is an indication of how serious the situation has become," said Achim Steiner, the agency's executive director, at a meeting in Johannesburg, South Africa.