Even the world's biggest funds are at it now. More of them are turning towards socially responsible investment, with investment funds totalling trillions of dollars now endorsing the UN-backed Principles for Responsible Investment.

There is no doubt that ethical investment is gaining traction. Peter Kinder, the president of Boston-based KLD Research and Analytics puts it down to climate change and explains why in this interview.

But the big questions remain unanswered: Does ethical investment deliver? And how exactly do you classify a company as clean? Is, for example, a company which produces life-saving drugs still responsible if it refuses lower its prices in poor countries? Is a woodchip company irresponsible if it provides employment and training in impoverished areas while ripping up old growth forests? And as an ethical investor, do you shun wicked companies, or do you try and change them from within?

Mother Jones tries answering that last question with the piece Confessions of a 401 (k) Schizophrenic. The answer, according to the writer Dashka Slater, is you can be an ethical investor in a number of ways, even investing in climate change denier like Exxon Mobil.

But does virtue pay? Do ethical companies really outperform the market, as their proponents claim. The answer is yes and no, according to research that's just come out of the University of New South Wales.

The study found little evidence that ethical investment portfolios outperformed the market simply because of purported goodness. On the other hand, the study found no evidence of underperformance either. The portfolios tended to do well because they had a bias towards growth stocks. Or as the study's author, Professor John Evans told me: ''If you were a fund manager, why would you construct a portfolio that's going to lose money?"