Advocates of hydrogen hope it can be produced and used on a large scale in transport and heavy industries in the future, providing a clean alternative to fossil fuels as it only emits water vapours.

But the research published in the journal Nature found that hydrogen has played a part in rising temperatures by helping methane, a potent greenhouse gas, stay longer in the atmosphere.

Emissions of hydrogen rose between 1990 and 2020, contributing a fraction of a degree -- or 0.02C -- to the nearly 1.5C increase in average temperatures since the pre-industrial period, the research found.

"We need a deeper understanding of the global hydrogen cycle and its links to global warming to support a climate-safe and sustainable hydrogen economy," said Stanford University scientist Rob Jackson, the paper's senior author.

The study, by an international consortium of scientists known as the Global Carbon Project, found that the increase in hydrogen emissions is mostly due to human activity.

Its rise is linked to the increase in methane emitted by fossil fuels, livestock and landfills, the researchers said.

The two molecules are intertwined: methane produces hydrogen when it breaks down in the atmosphere.

While hydrogen itself is not a pollutant, it indirectly contributes to warming by absorbing natural detergents that destroy methane, a potent greenhouse gas that has a shorter lifespan than carbon dioxide.

"More hydrogen means fewer detergents in the atmosphere, causing methane to persist longer and, therefore, warm the climate longer," said the study's lead author, Zutao Ouyang, an assistant professor of ecosystem modelling at Auburn University in Alabama.

Its interactions with natural detergents also affect cloud formation and produce greenhouse gases such as ozone and stratospheric water vapour.

Other sources of hydrogen in the atmosphere since 1990 include leaks from industrial hydrogen production.

Hydrogen can be manufactured by passing an electric current through water to split it between hydrogen and oxygen, a process called electrolysis.

Today, however, most hydrogen is produced from natural gas or coal in energy-intensive processes that emit large amounts of carbon dioxide.

The goal is to produce "green" hydrogen at scale using renewable energy instead, but the process is expensive and the sector has faced considerable hurdles.