In this age of explosive expansion in nearly every aspect of human endeavour our ability to make accurate forecasts is becoming increasingly important. We cannot wait until we run out of oil to find a new source of energy. We cannot wait until we can't stand living on the earth to slow down the rate of pollution. We cannot wait until there is no room left to stand on dry land before we do something about birth rate. We must predict what is likely to happen as a result of trends and then find ways either to change the trends or protect ourselves from the consequences.