Towers Watson acknowledges that investors can't plan for every potential risk to their portfolios, but in a new report it recommends that investors take into consideration not just financial or economic risks but political, social, environmental and technological risks as well.

The author of the report – Extreme Risks 2013 – encourages investors to be open-minded, avoid concentrated risks, be sensitive to early warning signs, constantly adapt and always prepare for the worst.

The top "extreme risks" for 2013 are food, water and energy shortfalls; stagnation, which is a period of little or no economic growth; global temperature change; depression, or a deep trough in economic output with massive increase in unemployment; global trade collapse; a banking crisis that stems from a lack of liquidity; sovereign default where a major sovereign borrower defaults on its loans; a currency crisis where there is extreme movement between exchange rates; deflation; a major health pandemic; nuclear contamination, extreme long life, insolvency within the insurance sector, terrorism and an interruption of a major infrastructure network.