In the Guardian story some additional information is presented to draw the parallel to the housing bubble and financial crisis. It states that international climate negotiations and the 2 degree limit would cause this to happen:
But meeting this limit would mean just 20% of existing fossil fuel reserves could be burned, according to recent research.To me, it seems implausible to expect a climate treaty any time soon that would lead to a situation where we leave 80% of fossil fuels untouched, especially given the high prices and profitability of oil, the dash for shale gas, the resurrection of coal power plants in Germany and elsewhere, etc. I am not sure if the spin in the Guardian story helps the effort to redirect long term investment, as stated in the letter. Relying on wishful thinking and scaring people will not work. After all, there is a different conclusion Sir Melwyn might draw: if such a systemic risk exists, better protect fossil fuel interests.