If you ask British scientist James Lovelock about the future of humanity, be prepared for a shock.

Writer Decca Aitkenhead of the London-based Guardian newspaper recently spoke with the 88-year-old independent scientist, inventor and author, and found his predictions "unnerving" and "alarming" — especially because Lovelock has a solid record when it comes to making predictions.

Ironically, Aitkenhead also found Lovelock surprisingly cheerful and insistent that he is an optimist — at least over the long term.

Forty years ago, when Shell Oil executives wanted to know what the world would be like in the year 2000, they asked Lovelock.

"He predicted that the main problem in 2000 would be the environment. 'It will be worsening then to such an extent that it will seriously affect their business,' " he told Shell, Aitkenhead notes in her article published March 1 in The Guardian.

A decade later, in the 1970s, Lovelock formulated the Gaia Theory, suggesting that Earth functions in a way similar to a self-regulating, "living organism." At first this was considered a bit wacky, but the tenets of Gaia are now mainstream science.

So what did Lovelock say that unnerved Aitkenhead?

"Enjoy life while you can," he told her. "Because if you're lucky it's going to be 20 years before it hits the fan."

But the sun keeps rising, bills keep piling up, and for now global recession appears a far more tangible threat than global famine or rising sea levels. For most people, worrying about the future still seems like a vaguely academic self-indulgence.

Lovelock is not alone, however. Anyone keeping track knows that more and more learned experts are calling for immediate action on global climate issues.

Two such experts are Lester Brown, president of the Earth Policy Institute in Washington, and Jeffrey Sachs, director of the Earth Institute at Columbia University, in New York.

I haven't yet had the pleasure of speaking with Lovelock, Brown or Sachs, but a look at their work offers an opportunity to triangulate on the most critical issues that face humanity and the planet.

All three strongly agree that prompt and concerted action is needed to ensure supplies of food, energy and fresh water, and to deal with climate change, poverty and population, as well as the feedback loops that inextricably link all of these together.

If it sounds to you as though these guys are concerned about, well, most everything, you're right. However, their approaches and conclusions can differ dramatically.

All three see climate change as a primary threat.

"Temperatures will rise, reliable supplies of water will be disrupted, life in the oceans will be compromised, food production will decline, and there will be mass migrations to areas of the planet's surface which remain habitable," says Lovelock's Web site.

As for solutions, Lovelock has raised eyebrows with his support for nuclear power. "With fossil fuels currently the dominant source of energy, a large-scale switch to nuclear power [is] vital if electricity supplies are to continue reliably and carbon dioxide emissions are to be brought down," his Web site notes.

Brown, too, believes that dealing with human-generated emissions of greenhouse gases is key. "Business-as-usual is no longer a viable option," he states in a press release for his recent book, "Plan B 3.0: Mobilizing to Save Civilization."

The book offers a blueprint for "reversing the trends that are fast undermining our future." Its four overriding goals are to stabilize climate, stabilize population, eradicate poverty, and restore the Earth's damaged ecosystems. "Failure to reach any one of these goals will likely mean failure to reach the others as well," he explains.

But to reduce carbon emissions and stabilize climate, Brown spurns nuclear power, instead proposing dramatic increases in energy efficiency, widespread use of renewable energies, and reforestation. He is particularly enthusiastic about wind power. "It is abundant, low cost, and widely distributed; it scales easily and can be developed quickly," he says.

Lovelock, in contrast, believes wind power is too little too late.

"You're never going to get enough energy from wind to run a society such as ours. Windmills! Oh no. No way of doing it. You can cover the whole country with the blasted things, millions of them. Waste of time," he glibly tells Aitkenhead.

But Brown, a solutions-oriented numbers-cruncher, cites Texas as an example of proactive renewable energy development. Texas plans to build 23,000 megawatts of wind-generating capacity (the equivalent of 23 coal-fired power plants, according to Brown), enough to provide residential energy for half the state's population of 22 million.

Something else all three researchers agree on is the need for wartime urgency in dealing with these global challenges — no doubt because the problems are huge and will require the focusing of maximum resources and ingenuity.

It may also be because unless the United States takes a leading role, there is a good chance we will not succeed in tackling these problems. And, since the U.S. rallies most effectively when it has an enemy, a call to battle may be the best way to galvanize America into action.

A wind revolution, like a war, would put Americans to work, notes Brown.

"The goal is to develop at wartime speed 3 million megawatts of wind-generating capacity by 2020, enough to meet 40 percent of the world's electricity needs. This would require 1.5 million wind turbines of 2 megawatts each. These turbines could be produced on assembly lines by reopening closed automobile plants, much as bombers were assembled in auto plants during World War II," he explains.

Lovelock, too, says wartime-focus is needed.

Talking about how World War II inspired people to action, he notes that "everyone got excited, they loved the things they could do, . . . so when I think of the impending crisis now, I think in those terms. A sense of purpose — that's what people want," he tells Aitkenhead.

For Sachs, it's time to substitute one war for another.

"If the trillions of dollars that the U.S. is squandering in Iraq was instead being invested in clean energy, disease control and new, ecologically sound ways of growing food, we wouldn't be facing the cusp of a rapidly weakening dollar, soaring food and energy prices and the threats of much worse to come," he states in a Time magazine essay this month, titled "Common Wealth."

Sachs sees four goals that Washington and the rest of the world must focus on, calling these "bold but achievable." They are: sustainable systems of energy, land and resource use to counter climate change, species extinction and destruction of ecosystems; stabilization of human population at 8 billion or below by 2050; the end of extreme poverty by 2025; and "a new approach to global problem-solving based on cooperation among nations and the dynamism and creativity of the nongovernmental sector," he writes.

All three researchers also share a sense of optimism — sort of: from Lovelock's hope that we will gain wisdom through failure to Sachs' invoking of John F. Kennedy's words in a call for global unity and action.

"There have been seven disasters since humans came on the Earth, very similar to the one that's just about to happen," says Lovelock. "I think these events keep separating the wheat from the chaff. And eventually we'll have a human on the planet that really does understand it and can live with it properly. That's the source of my optimism," Lovelock tells the Guardian's Aitkenhead.

Brown hasn't written us off yet, but he insists that time is crucial.

"It is decision time. Like earlier civilizations that got into environmental trouble, we can decide to stay with business as usual and watch our modern economy decline and eventually collapse, or we can consciously move onto a new path, one that will sustain economic progress. In this situation, no action is a de facto decision to stay on the decline-and-collapse path," he says in a piece written by Tim Montague in the March 13 edition of Rachel's Democracy & Health News.

Sachs, too, notes that we must be resolute in embracing change.

"We will need science, technology and professionalism, but most of all we will need to subdue our fears and cynicism," he writes.

He concludes his essay with a quote from JFK: "If we cannot end now our differences, at least we can help make the world safe for diversity. For, in the final analysis, our most basic common link is that we all inhabit this small planet. We all breathe the same air. We all cherish our children's future. And we are all mortal."

Given a choice between the smug fatalism of Lovelock and the tough-choice optimism of Brown and Sachs, I choose the latter. I can understand Lovelock's resignation, but I'm an optimist, too, and I think we should do our damnedest to leave the world in a bit better shape than it is today.

In all honestly, I'd also rather see millions of wind generators turning gracefully in the breeze than live to see my son's future hitting the fan.

Stephen Hesse welcomes readers' comments at [email protected]