About a dozen years ago geologists were startled to discover that — contrary to previous belief — underground hydrogen deposits existed in potentially significant reserves. It was in the West African nation of Mali that an engineer digging a water well happened upon a shallow deposit of pure hydrogen. Tests confirmed the well was producing 98 percent pure hydrogen.

Those in the geological sciences had to do a double clutch on the matter. Their revised estimate: There could be trillions of tons of hydrogen trapped below the Earth’s surface, sitting in wait for humanity to exploit what could become a pervasive source of clean energy, giving the global campaign to reduce carbon emissions a pivotal boost.

Unlike fossil fuels, hydrogen emits no greenhouse gases, only heat and water, which is why advocates for decarbonizing the economy find it so compelling. Though it would be accessed through a drilling process similar to oil and natural gas, hydrogen doesn’t pollut