Have you ever imagined what the world will be in the near future? A recent study shows that the world in 2100 will be more crowded, more polluted and less stable ecologically than the world we live in now. Visible ahead is serious stress involving population, resource and environment. Despite greater food output, people in the world will be poorer in many ways than they are today.     For hundred of millions of the extremely poor, the outlook for food and other necessities of life will be no better, for many it will be worse. While the economies of the developing countries are expected to grow at a faster rate than those of the industrialized nation, the total national product per head in most less developed countries remains low. The existing gap between the rich and poor nations will further widen. World food production is estimated to increase by 90 percent from 2000 to 2100. Most of that increase goes to the countries that already have   higher per-head food consumption. Meanwhile, per-head consumption of food in the developing countries will scarcely  improve or will actually fall far below the present inadequate level. What is worse is that prices for food are expected to double. As a result, many less developed countries will have increasing difficulties meeting energy needs. For the one quarter of mankind that depends primarily on wood for fuel, the outlook is not hopeful. Regional water shortage will become more sever. In the 1970-2100 period population growth will require twice as much water as it does today in nearly half the world. Still greater increases would be needed to improve standards of living. Development of new water supply will become more costly. The passage is mainly concerned about   _  .
the future problems in the world water and air pollution water and food shortages food production and consumption