It is the most common element in the universe, one of the key building blocks of life and the fuel that makes stars burn bright.

But hydrogen, an invisible gas that experts say is major part of the solution to stopping climate change, is in surprisingly short supply.

Hydrogen burns cleanly and can replace dirty fuels in industries like steelmaking and shipping, where electric processes are unsuitable or expensive. But the molecule is so reactive that it is almost never found in its pure form. To honor their promises to stop the planet heating, world leaders need to make lots more hydrogen — and fast.

"It will be extremely challenging to scale up renewable hydrogen production at the pace required to keep the planet from warming by less than 1.5 degrees Celsius [2.7 Fahrenheit]," said Alejandro Nunez-Jimenez, who researches hydrogen at the Swiss Federal Institute of Technology in Zurich.

Race for cleaner hydrogen

Experts use colors to refer to different ways of making hydrogen — some of which are cleaner than others — and disagree fiercely over which types should be supported.

Green hydrogen is made using electricity from renewable sources to split water molecules into hydrogen and oxygen atoms. Gray hydrogen, which accounts for nearly all hydrogen produced today, is made with methane gas and steam in a chemical process that emits carbon dioxide. Blue hydrogen is made with the same process, but the carbon is captured and stored.

If all the electricity to make green hydrogen comes from dams, wind turbines or solar panels, the result is a fuel that does not heat the planet. If engineers get better at capturing carbon — and gas companies plug methane leaks — the emissions from making blue hydrogen could be low enough to speed the shift to a clean economy.

Done badly, producing blue hydrogen can be dirtier than directly burning fossil gas. 

"Too many factors conspire in making blue hydrogen much more challenging than renewable hydrogen," said Nunez-Jimenez, adding it could play a useful role in some settings.

Demand for hydrogen is set to soar as subsidies flow into clean technologies and lawmakers raise the price of polluting the atmosphere. In the United Sttes, a climate law passed in August put a price on methane pollution and gave tax incentives to capture carbon. Weeks later, the European Union announced €5.2 billion ($5.7 billion) in funding for hydrogen projects it hopes will kick-start private investments.

If all planned projects go ahead, production of blue and green hydrogen will rise from less than 1 megaton in 2021 to about 20 mt by the end of the decade, according to the International Energy Agency (IEA), an organization led by the energy ministries of mostly rich nations. To reach net-zero emissions by 2050, the sector would need to be making 100 mt of blue and green hydrogen by 2030.

Why can't the world make more green hydrogen right now?

Two obstacles stand in the way of making green hydrogen, which today accounts for less than 1% of the world's hydrogen production. The first is building electrolyzers to get hydrogen from water.

Electrolyzers, which break water molecules into hydrogen and oxygen, are being built at record rates. Installations tripled between 2020 and 2021, according to the IEA, but are starting from a very low base and are a long way from meeting climate targets.

Several barriers hold back the industry, including the short supply of iridium and platinum. These expensive metals are used as catalysts for the chemical reaction in a common type of electrolyzer.

"If that cost comes down, the total cost comes down," said Neethu Varghese, a hydrogen researcher at the University of Genoa in Italy.

But experts say the scale of the challenge is hard to grasp. Even if electrolysis capacity were to grow as fast as wind and solar power — the biggest success stories of the energy transition — green hydrogen will make up less than 1% of final energy demand globally by 2035, according to a study published in the journal Nature in September.

Still, the scientists found technologies that had grown faster than renewables — with the right support. The US manufactured fighter planes at unprecedented speeds during World War II. France poured public money into its nuclear industry in the 1970s. And China coordinated construction of the world's biggest high-speed rail network in a decade.

By taking an "emergency" approach to green hydrogen, policymakers could close the gap between supply and demand, the authors found.

Renewable energy shortages

The second hurdle is the cost and availability of renewable energy that can power the process cleanly.

In many regions, green hydrogen has been able to compete with gray hydrogen on cost since Russia invaded Ukraine and sent gas prices soaring, according to the IEA.

Still, building enough wind turbines and solar panels to make green hydrogen is tricky. Estimates vary for how much is needed by 2050, but "to decarbonize electricity and to have clean hydrogen means a ramp up of 15-20 times today's renewable generation," said Gniewomir Flis, an independent clean technology consultant.

There are three big bottlenecks, he added. The first is the raw materials and factories to build hardware like turbine blades and solar panels. Then there's local opposition and rules that slow planning. And lastly there are high energy prices, which bump up costs of building the required hardware and make it harder to get loans.

A lifeline for fossil gas

By betting on green hydrogen to clean up parts of the economy, critics have said policymakers risk locking in fossil fuels.

In Germany, politicians have approved fossil gas pipelines and built liquefied natural gas (LNG) terminals, saying they are now "hydrogen-ready." However, LNG terminals will need to be replaced, and the pipelines would likely need to be retrofitted to carry hydrogen, said Flis.

"It's not accurate to describe an LNG terminal as hydrogen ready per se," said Flis, adding that converting one to import hydrogen was so difficult it was unlikely to happen.

Similar problems could happen in other sectors. If supplies of green hydrogen stay short, steelmakers who ditch coal-fired furnaces will burn fossil gas instead.

Vaitea Cowan, CEO of electrolyzer maker Enapter, said policymakers need to "clearly define what renewable hydrogen is" to help the industry attract funding. They also need to "stop subsidizing fossil fuels," she added.

Edited by: Jennifer Collins