Within the next 50 years, the earth's population will probably pass 9 billion, and global economic output may quintuple. Largely as a result, renewable resources will become increasingly scarce. The total area of agricultural land will shrink, Many remaining virgin forests will be lost. Overuse and pollution of aquifers, rivers and other water supplies will continue. Thinning of the ozone layer will probably worsen. Such scarcities could spark violent civil or international conflict.