Green investment is all the rage. But does it deliver? Does it pay off and produce strong profits for the investor.

This piece in the latest edition of The Economist, Backing greens with greenbacks, advises us to exercise some caution.

"Most green companies are not a matter of a couple of geeks and a website. Just as telecom companies laid down billions of dollars worth of fibre-optic cables, environmental companies require large amounts of capital-for building a wind farm or a tidal barrage-or the patience to invest in new technologies, such as cellulosic ethanol or thin-film solar panels.

"This means that the shares are likely to be volatile. The returns are highly uncertain, because the big profits (if any) are many years away. News events such as technological breakthroughs or changes in government policy will have a much bigger impact on valuations."

Part of the problem is the many competing solutions to climate change. One day it's solar, the next day it's wind, then it's geothermal energy. Which makes it very hard for investors to pick winners.

But while climate change and oil prices remain key issues, there will be no shortage of investors willing to put up the money. They should not expect immediate returns.