Anyone tired of lousy news from the markets should talk to Douglas Lloyd, a director of Venture Business Research, which tracks trends in venture capitalism. "I expect investment activity in this sector to remain buoyant," he said recently. Lloyd's bouncy mood was inspired by the money that is gushing into private security and defence companies. He added: "I also see this as a more attractive sector, as many do, than clean energy."

Got that? If you are looking for a sure bet in a new growth market, then sell solar and buy surveillance: forget wind, buy weapons.

This observation - coming from an executive who is trusted by such clients as Goldman Sachs and Marsh & McLennan - deserves particular attention in the run-up to the United Nations climate change conference, which takes place in Bali next week. There, world environment ministers are supposed to come up with the global pact that will replace the Kyoto agreement.

The Bush administration, still roadblocking firm caps on emissions, wants to let the market solve the crisis. "We're on the threshold of dramatic technological breakthroughs," the American president assured the world last January, adding: "We'll leave it to the market to decide the mix of fuels that most effectively and efficiently meet this goal."

The idea that capitalism can save us from climate catastrophe has powerful appeal. It gives politicians an excuse to subsidise corporations rather than to regulate them; and it neatly avoids a discussion about how the core market logic of endless growth landed us here in the first place.

The market, however, appears to have other ideas about how to meet the challenges of an increasingly disaster-prone world. According to Lloyd, the really big money - despite all the government incentives - is turning away from clean-energy technologies, and is banking instead on gadgets that promise to seal wealthy countries and individuals into hi-tech fortresses. Key growth areas in venture capitalism are private security firms selling surveillance gear and privatised emergency response. To put it simply, in the world of venture capitalism, there has been a race going on between greens on the one hand, and guns and garrisons on the other - and the guns and garrisons are winning.

According to Venture Business Research, last year North American and European companies developing green technology were neck and neck in the contest for new investment with those companies that focused on "homeland security" and weaponry: green tech received $3.5bn (£1.7bn), and so did the guns-and-garrisons sector. But this year, guns and garrisons have suddenly leapt ahead. The greens have received $4.2bn, while the garrisons have nearly doubled their money, collecting $6bn in new investment funds. And 2007 isn't over yet.

This trend has nothing to do with real supply and demand, since the demand for clean-energy technology could not be higher. With oil now reaching nearly $100 a barrel, it is clear that we badly need green alternatives, both as consumers and as a species. The latest report from the Nobel prize-winning UN Intergovernmental Panel on Climate Change was characterised by Time magazine as "a final warning to humanity", while a new Oxfam report makes it clear that the recent wave of natural disasters is no fluke: over the past two decades, the number of extreme weather events has quadrupled. Conversely, this year has seen no major terrorist events in North America or Europe, there are hints of a United States troop drawdown in Iraq, and, despite the relentless propaganda, there is no imminent threat from Iran.

So why is "homeland security", not green energy, the hot new sector? Perhaps because there are two distinct business models that can respond to our climate and energy crisis. We can develop policies and technologies to get us off this disastrous course. Or we can develop policies and technologies to protect us from those we have enraged through resource wars and displaced through climate change, while simultaneously shielding ourselves from the worst of both war and weather. (The ultimate expression of this second option is in Hummer's new television adverts: the gas-guzzler is seen carrying its cargo to safety in various disaster zones, followed by the slogan "HOPE: Hummer Owners Prepared for Emergencies". It's a bit like the Marlboro man doing grief counselling in a cancer ward.) In short, we can choose to fix, or we can choose to fortress. Environmental activists and scientists have been yelling for the fix. The homeland security sector, on the other hand, believes the future lies in fortresses.

Though 9/11 launched this new economy, many of the original counterterrorism technologies are being retro-fitted as privatised emergency response during natural disasters - Blackwater pitching itself as the new Red Cross, firefighters working for insurance giants. By far the biggest market is the fortressing of Europe and North America - Halliburton's contract to build detention centres for an unspecified immigration influx, Boeing's "virtual" border fence, biometric ID cards. The primary targets for these technologies are not terrorists but migrants, an increasing number of whom have been displaced by extreme weather events such as the recent floods in the Mexican state of Tabasco, or the cyclone in Bangladesh. As climate change creates more landlessness, the market in fortresses will increase dramatically.

Of course, there is still money to be made from going green; but there is much more green - at least in the short term - to be made from selling escape and protection. As Lloyd explains: "The failure rate of security businesses is much lower than clean-tech ones; and, as important, the capital investment required to build a successful security business is also much lower." In other words, finding solutions for real problems is hard, but turning a profit from those problems is easy.

Bush wants to leave our climate crisis to the ingenuity of the market. Well, the market has spoken: it will not take us off this disastrous course. In fact, the smart money is betting that we will stay on it.

· A version of this article appears in the Nation (www.thenation.com) www.naomiklein.org