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In the modern world, a reliable supply of hydrogen gas is vital for the function of society. Fertilizer produced from hydrogen contributes to the food supply of half the global population, and hydrogen is also a key energy component in many roadmaps to a carbon-neutral future, essential if we are to prevent the worst predictions of climate change.

Today, hydrogen is produced from hydrocarbons, with waste gases contributing to 2.4% of global CO₂ emissions. Demand for hydrogen is set to increase from 90 million metric tons in 2022 to 540 million metric tons in 2050, but it is vital that this hydrogen is not CO₂ emitting.

Production followed by the burial of waste CO₂ ("carbon sequestration") or from renewable energy resources (wind or solar) are both future sources of hydrogen, but are not yet commercially competitive.

New research from the University of Oxford, in collaboration with Durham University and the University of Toronto, provides a solution. The work is published in the journal .

In the last billion years, enough hydrogen gas has been produced by Earth's continental crust to supply mankind's energy needs for at least 170,000 years. While a proportion of this has been lost, consumed, or is inaccessible today, the remaining hydrogen could offer a natural (and emission-free) source of this natural resource.

Until now, limited historical hydrogen sampling and measurement have restricted scientists' current understanding of where, and how much, hydrogen is located in the crust. An exploration recipe is critical to find accessible and commercially viable accumulations of natural geological hydrogen.

Study co-author, Professor Jon Gluyas (Durham University) notes, "We have successfully developed an exploration strategy for helium and a similar 'first principles' approach can be taken for hydrogen."

This research outlines the key ingredients needed to inform an exploration strategy to find different "hydrogen systems." This includes how much hydrogen is produced and the rock types and conditions these occur in, how the hydrogen migrates underground from these rocks, the conditions that allow a gas field to form, and the conditions that destroy the hydrogen.

Study co-author Professor Barbara Sherwood Lollar (University of Toronto) said, "We know, for example, that underground microbes readily feast on hydrogen. Avoiding environments that bring them into contact with the hydrogen is important in preserving hydrogen in economic accumulations."

The authors outline where understanding of these ingredients is strong, and highlight areas that need more work鈥攕uch as rock reaction efficiencies and how geological histories can bring the right rocks together with the water that reacts with it.

Some sources of hydrogen gas, such as from Earth's mantle, have fueled much speculation and hyperbole鈥攂ut this research shows that these are not viable sources. Instead, the authors showed that the ingredients for a complete hydrogen system can be found in a range of common geological settings within the crust.

Some of these can be geologically quite young, forming hydrogen "recently" (millions to tens of millions of years), others are truly ancient (hundreds of millions of years old)鈥攂ut critically found globally.

Lead author Professor Chris Ballentine (University of Oxford, Department of Earth Sciences) said, "Combining the ingredients to find accumulated hydrogen in any of these settings can be likened to cooking a souffl茅鈥攇et any one of the ingredients, amounts, timing, or temperature wrong and you will be disappointed.

"One successful exploration recipe that is repeatable will unlock a commercially competitive, low-carbon hydrogen source that would significantly contribute to the energy transition鈥攚e have the right experience to combine these ingredients and find that recipe."

The potential for natural geological hydrogen has motivated the authors to form Snowfox Discovery Ltd., an exploration company with a mission to find societally significant natural hydrogen accumulations.