There’s one basic answer to the question, Why are we worried about energy? The answer is climate change, argues MIT’s Ron Prinn: if there were no global warming threat associated with fuels like oil and coal, there’d be no crisis.

In the U.S., for example, it’s possible to imagine scenarios in which we get by without any oil at all. “If it’s energy security the country is worried about,”says Prinn, “we can use coal.”

America has coal in abundance: 30 percent of the world’s proven reserves, or enough to meet U.S. energy needs for 400 years. But climate change concerns, at least for now, effectively rule out any such strategy, notes Prinn. That’s because coal generates high levels of carbon dioxide, the main “greenhouse gas” associated with the threat of global warming.

“Coal produces CO2 in much larger amounts, per unit of energy, than either oil or natural gas,” he observes.

That’s a problem because CO2 builds up in the atmosphere. The result, more and more studies show, is a warming of the planet as the CO2 traps increasing amounts of heat.

Its CO2-related impacts mean coal can’t come to the U.S.’s rescue in the near term. But is the country’s sole choice to seek alternatives to the big three CO2-generating fuels?

Prinn — a professor of meteorology who’s a strong advocate of limiting CO2 emissions — says that taking the long view, we may not have to curtail our reliance on fossil fuels as sharply as many fear. It depends on whether we can remove CO2 from the combustion stream and store it in deep underground reservoirs. “If we solve all the problems involved in sequestering carbon,” he says, “then in my view, fossil fuels can still have wide applicability.”

An MIT group, in fact, is working to overcome the hefty technological and economic obstacles to storing CO2 underground. But whether that breakthrough occurs or not, Prinn says there may still be barriers to a massive switch-over to renewable energy sources — solar, wind, hydro-power, and wave energy, among others. Some of those barriers, ironically, are environmental.

First, the big picture: translated into electric power terms, the world’s total energy consumption is an estimated 14 terawatts — that is, 14 trillion watts. “And people project that we’ll need up to 30 terawatts by mid-century,” notes Prinn.

Suppose you wanted to get 10 percent of that from added wind power. “How many windmills does it take to supply that much energy?” asks Prinn. “Nobody knows the exact answer, but with typical one-megawatt windmills, it would be three million.”

Putting aside key issues like economic viability, and the aesthetic and ecological implications of the amount of land or sea surface required by that many windmills, what would such buildup mean for one natural phenomenon that affects all of us — the weather?

Those windmills, says Prinn, would “take significant momentum out of the atmosphere, so there’d be less penetration of wind to the ground surface.” That being so, it’s logical to assume a massive windmill deployment could at least alter regional weather patterns.

Prinn emphasizes he’s not against wind power or any other renewable energy technology. He simply thinks it’s essential to explore how any of the proposed technologies might affect us. “We don’t just need to look at the lab scale or the pilot program scale,” he says, “but at the scale at which one of these technologies can supply one or more terawatts of power. We need to recall the lessons from the chlorofluorocarbons, which were perfect refrigerants at small scales but became an environmental disaster when emitted into the atmosphere in large quantities.”