The warming potential of hydrogen as an indirect greenhouse gas has been shown to be higher than previously reported and with a greater degree of certainty, according to a new study published today (Wednesday).

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Climate scientists from four countries and across six different institutions — led by Norway’s CICERO Centre for International Climate Research — estimated in the academic paper published in the journal Nature, that the Global Warming Potential of hydrogen over a 100 year period (GWP100) is 11.6 ± 2.8, slightly higher than a landmark UK study found last year.

In practice this means that the GWP of atmospheric hydrogen could be between 8.8 and 14.4 depending on a range of factors, including how much hydrogen is absorbed into soil at ground level and how effectively it interacts with other airborne molecules that cause global heating.

Around 65-85% of all atmospheric H2 absorption is achieved through the soil, making it a major “hydrogen sink”.

Hydrogen is considered an indirect greenhouse gas because although it does not cause a warming effect on its own, it interacts with airborne molecules called hydroxyl radicals to prolong the lifetime of atmospheric methane — a highly potent greenhouse gas — and increase the production of ozone, another greenhouse gas.

The paper, which used five different modelling techniques to arrive at its conclusions instead of the typical one, also calculated that the GWP over 20 years for hydrogen is a whopping 37.3 ± 15.1, while over 500 years it is minimal at 3.31 ± 0.98.

GWP is measured against the warming potential of a kilogram of carbon dioxide, meaning that in the study’s central range, a kilogram of hydrogen would have the same warming effect as 11.6 kilograms of CO2.

This is higher than the UK government’s estimate of 11 ± 5, unveiled last year, which itself doubled previous estimates of hydrogen’s GWP100.

Prior to this, the most frequently-cited paper estimated the GWP100 of hydrogen at just 5.8.

Two further academic papers cited in the Nature study found that hydrogen’s GWP100 was even higher, with one published last year estimating it at 12.8 ± 5.2, and another still in review coming in at 12 ± 6.

But significantly, the Oslo-led study, which also included work from the US government’s National Oceanic and Atmospheric Administration and France’s Université Paris-Saclay, as well as the University of California and the University of Edinburgh, came up with a smaller range around its central figure of 11.6, indicating a higher degree of certainty.

This could be because the researchers used five different global atmospheric modelling systems to arrive at their conclusion.

“It will be important to keep hydrogen leakages at a minimum to accomplish the benefits of switching to a hydrogen economy,” the study warned.