The center of the Earth is a roiling ball of heat, roughly 6,000 degrees Celsius as near as we can tell without a sci-fi tunneling effort. The closest humanity has come to that molten core is some 12 kilometers beneath the continental crust in Russia, which isn't even halfway through said crust and akin to drilling into an apple without piercing the skin. Yet, it's pretty clear that a lot of that core and mantle heat makes its way to or near the surface—witness: Yellowstone, the big island of Hawaii, all of Iceland—offering a cheap, constant and potentially clean source of energy.

There are already several methods for harvesting the energy in this rock that's heated by the decay of radioactive elements. It's also something humans have been doing for a long time—at least since 1911 in Italy to be exact when locals opened the world's first geothermal power plant in the Valle del Diavolo. We even have an industry devoted to refining and improving the drilling techniques to make such energy available on an even grander scale—you know it as the most profitable enterprise on the planet, yes, the oil and gas industry.

So why in the world don't we use more geothermal energy? "All the energy we need is right beneath our feet," argues geologist Craig Dunn, chief operating office of Borealis GeoPower, a Canadian geothermal developer, an advisor to the Equinox Summit and its search for alternative energy technologies. The summit paired "future leaders" with old-school scientists to develop a plan to cut greenhouse gas emissions, enhance energy security and extend modern energy to the billions of people who do not presently enjoy it. Geothermal could play a key role. As Dunn says: "the top one percent of the planet has enough energy to power and heat civilization for approximately 6 billion years."

As it stands, geothermal accounts for roughly 0.3 percent of global electricity generation.  A big chunk of that comes from one power plant at The Geysers in Northern California. Other hotbeds of geothermal use range from the Philippines and Indonesia to Germany and Mexico. And there is plenty more to come by, for example in the volcanic seamounts of Hawaii, a state which currently relies on burning imported oil for 90 percent of its electricity, or using the heat in onsen (hot springs) as a replacement for nuclear power in Japan. Even California's Google has gotten into the act, sinking roughly $11 million into geothermal drilling research.

The volcanoes of Hawaii and hot springs of Japan are just the most obvious places to put a geothermal power plant. "We should hit the easiest stuff first," Dunn says, noting that the geothermal industry is still learning to prospect for "blind resources," or those for which there is very little or nothing evident on the surface in the way of hot springs, geysers or volcanoes. "We're where the oil and gas industry was in the 1940s and 1950s."

The International Energy Agency suggested in a road map for the technology's development released this week that geothermal could increase 10-fold by 2050 if the right financial and policy incentives are put in place—along with research funding for more advanced systems, known as enhanced geothermal (or EGS). EGS involves drilling into the Earth, fracturing the hot rock below and then pumping water (or other working fluids) down to capture the heat and return it to the surface—mimicking the kind of heat flow that occurs naturally at a geyser. 

Australia is helping lead the charge to develop such EGS technology, via various drilling programs, the most prominent of which is in the Cooper Basin in the nation's central desert country. But the companies involved have struggled mightily with drilling risks and financial challenges—a global problem. "Until you get down there, you don't know the temperature," explains engineer Robin Batterham of the University of Melbourne, former chief scientist of Australia and mining company Rio Tinto. "Until you drill a couple of wells you don't know how well it will flow."

Drilling a several-kilometer-deep well costs millions of dollars, and one needs at least five such wells (and possibly as many as 50) to prove a given geothermal resource is going to reliably deliver heat with which to make electricity. The "dry hole"—in this case one that doesn't produce steam—is just as much a challenge for geothermal as it is for oil and gas.

Plus, there's the fact that drilling for geothermal can set off mini-earthquakes (although this doesn't seem to bother us as much about drilling for oil or natural gas.) An international, coordinated effort to demonstrate the potential of the technology—as has been done for carbon capture and storage—might help overcome these challenges, and that's what participants in the recent Equinox Summit called for, along with a billion dollars in funding for such demonstration projects.

There's also the simple fact that one can drill to release a transportable commodity worth roughly $100 per barrel (aka oil) or one can drill to produce a commodity that must be instantaneously transported and consumed at a value of roughly 10 cents per kilowatt-hour (aka geothermal electricity). In the absence of a price for using the atmosphere as a dumping ground for the CO2 produced by burning fossil fuels like coal or oil, the dollars and cents of even free hot rocks may not add up. And that's too bad for the global climate.

Image: Photograph by Julie Donnelly-Nolan, USGS