Unless you live under a rock, you can't avoid all the bad news about the environment. Global warming, carbon footprints, extreme weather, rising sea levels, the possible extinction of polar bears--it's everywhere. Oh, and at our current rate of growth, there will be another 3 billion people on the planet within the next 40 years, up from 6 billion today.

As a market , "cleantech" is large and growing. According to a report by CleanEdge Inc., company revenue in the biofuel, wind, solar-photovoltaic and fuel cell markets is expected to top $250 billion within the decade, up from $77 billion last year. And global investment in energy technologies reached close to $150 billion in 2007, according to research firm New Energy Finance, as reported by CleanEdge in its 2008 report.

"The market size for cleantech will be measured in the trillions of dollars -- it's immeasurably deep," said Erik Straser, partner and leader of the cleantech team at venture capital firm Mohr, Davidow Ventures (Palo Alto, Calif.) Mohr, Davidow has investments in 11 cleantech companies to date, including those exploring solar, biofuel and hydrogen fuel cell technologies.

According to Straser and other investors, we are in the early stages of an investment boom that will last 20 to 30 years. To date, the cleantech business has been driven by a relatively small number of venture capitalists and entrepreneurial companies. But that's now changing. "Cleantech is going mainstream," Straser said.

Indeed, mainstream venture capital firms, corporate capital funds and even nations are beginning to pour billions into the sector. China, which surpassed the United States in 2006 as the world's largest contributor to greenhouse gas emissions, is investing big in renewable-power technologies. The nation to date has plowed nearly $3 billion into wind power, $8.1 billion in solar thermal energy, $1.7 billion in solar photovoltaics, $3.1 billion in ethanol and $1.3 billion in biodiesel, according to Patrick Tam, general partner of Tsing Capital, as reported by China Daily earlier this year.

Venture capital investments in China are expected to nearly double, from about $400 million in 2006 to more than $720 million this year, according to Cleantech China Research.

India ranks fifth in the world in renewable-energy capacity. To meet the country's energy demand of the next 20 years, however, will require capital investment on the order of $200 billion.

Even oil-producing nations such the United Arab Emirates are pouring billions into cleantech ventures and a planned city. (See Building a Clean Tech City on the Persian Gulf , p.46.)