BBC: An increasingly popular tool in the fight against climate change is emerging - "divestment". The term refers to the shedding of stocks, bonds or other investments, in this case that are held in companies that produce or burn fossil fuels. As the world's leaders prepare for a make-or-break climate summit in November, will divestment change our relationship with fossil fuels - and what might the dangers be, asks our social affairs reporter John McManus? It began with a campaign on US university campuses....