Necessity may be the mother of invention, but without investment most inventions might as well have never been born. So it's exciting to survey the rising tide of capital flowing toward renewable energy and other earth-friendly sectors, as noted recently by such publications as Business Week and Newsweek. Consider these indicators:

• Investment in clean-energy projects climbed 89 percent in the United States from 2004 to 2005 — and 62 percent worldwide, for an estimated global total of $49 billion.

• Surging capital is not only bringing familiar technologies to the marketplace, it's encouraging development of alternatives to the alternatives — like cheaper ways of making solar electricity and plant-based ethanol.

• Investment banks are not only steering clients toward green energy companies, some — including Goldman Sachs and JPMorgan Chase — are buying the companies for themselves.

• The list of famously shrewd business visionaries making major investments in green businesses includes Warren Buffett, Bill Gates, Jeffrey Immelt, Richard Branson and L. John Doerr.

Somewhat inconsistently, Business Week attributes this phenomenon primarily to spiking oil prices while also noting that the trend was under way beforehand. We tend to think that investment giants don't make bets of this size for reasons as narrow as current oil prices.

For many years, Americans have displayed growing interest in earth-friendly alternatives for their own sake. There were waiting lines for hybrid-electric autos before gas prices went through the roof; "green power" programs offered by utilities were oversubscribed when rates were low; organic food sales have been growing at a faster pace than groceries overall for a decade or more.

Yes, consumer interest in energy efficiency has accelerated with surging oil prices, but it's a mistake to think that falling prices, if and when they arrive, will therefore cause that interest to fade.

By and large, Americans take global warming more seriously than their president does, and surveys have shown that a sizable portion will select sustainably produced products that are priced comparably to, or even slightly higher than, the usual stuff. It feels good and it does some good, too.

Still, small markets usually mean small profits, and pent-up demand remains just that until the makers of products and the managers of portfolios begin to see things the same way. That's the moment when big changes are possible, and it appears that such a moment may now be at hand.

Doubters who dismiss green products' market potential as fleeting trendiness need look no further than Wal-Mart's new interest in natural foods, organically grown cotton and ethanol pumps. Or the growth of organic food production into industrial systems indistinguishable in size or shape from conventional agriculture. Or the expanding interest in ecologically attuned buildings, both residential and commercial.

This is what the venture capitalists are paying attention to — and as Business Week puts it, "You know a cultural movement is real when the money men get on board."

— Star Tribune (Minneapolis)