I think it is possible to forecast using one's brains, but the person needs to have imagination and be able to see alternatives more clearly than the average. Choosing between possibilities is an art as well as a science. I learned from a master forecaster Professor Ronald Brech of Wimbledon, UK. He developed school business games and arranged competitions between schools throughout the UK to teach kids the arts of business and forecasting. Sadly, this was in the 1980's and one has to look very hard for a modern equivalent. Brech emphasized the interrelationships between the many qualitative visions of a community, and how difficult it is to grasp how technology or sociology will impact of a business product life cycle. In any event the art and skills of forecasting are very real and can change the world.
Use your imagination to see if you can envisage where world population and per capital income will go over the next fifty years.
http://opinionator.blogs.nytimes.com/2010/08/15/reclaiming-the-imagination/?th&emc=th
Will ye no think kindly on those who would be your friends! May the sun shine with your thoughts, today, and happiness grow in your heart! May you allow yourself some peace of mind.