Until recently, it was remarkably difficult for ordinary investors to put their own money behind the fight against global warming. Mutual funds, most people's investment vehicle of choice, offered few options.

That has changed thanks to government legislation and a new awareness among many of the world's investment professionals that climate change is an opportunity, not a threat. In a little more than two years, we estimate retail investors all over the world have pumped around $66bn (£33bn, €42bn) into more than 200 newly launched mutual funds and exchange traded funds investing in companies that help to mitigate or adapt to climate change.