Ramping up the use of blue hydrogen to just 30% of the H2 mix by 2050 could wipe out the climate benefits from the hydrogen economy over 20 years on account of fugitive methane emissions and the fact that not all the CO2 in the production process can be captured, climate scientists write in a new study.
That amount of blue hydrogen might even be worse for the environment than not using H2 at all, they add.
But hydrogen leakage from production and use of both blue and green hydrogen (made with renewable energy and electrolysis) would also have an enormous impact on the climate abatement potential of a hydrogen economy, defined by the study as 549 million tonnes of hydrogen demand per year by 2050.
The study, Climate Benefit of a Future Hydrogen Economy, published in scientific journal Nature, found that a hydrogen economy with a 70:30 ratio of green to blue hydrogen — assuming a hydrogen leakage rate of 10% across both blue and green — could push CO2-equivalent (CO2e) emissions to 153% of the six gigatonnes of carbon dioxide emissions abated over a 20-year period, effectively bringing about a “climate penalty” of 53%.
Once the blue hydrogen ratio grew over 30%, the climate penalty would apply even at low hydrogen leakage rates of 3%, the study’s authors said.
However the impact of a 30% blue hydrogen share is greatly reduced when measured over 100 years. On fact over this timeframe and at an H2 leakage rate of 7%, the blue hydrogen share would have to hit 60% for the climate penalty to kick in.
This is because methane and hydrogen are relatively short-lived greenhouse gases. Nevertheless, methane is up to 87 times’ more potent as a greenhouse gas over 20 years than carbon dioxide, and has 36 times’ more Global Warming Potential (GWP) over 100 years.
The study based its upstream methane emissions on figures from the US oil and gas industry, which are notoriously high compared to those in Europe.
It remains an open question about which of the 20- or 100- year GWPs are the most useful to measure, but with the latest IPCC report finding that climate change is speeding up, lawmakers may begin to consider the 20-year period as the best benchmark for making policy decisions.
A UK study published this year found that hydrogen, an indirect greenhouse gas because it prolongs the life of other greenhouse gases such as methane, has GWP of around 33 over 20 years, and between six and 16 over a 100 years.
As a result, the hydrogen leakage rate has a significant impact on the relative merits of a hydrogen economy met with either green or blue hydrogen.
At a hydrogen leakage rate of 15%, even a hydrogen economy made up of 100% green hydrogen would invoke a climate penalty of 67%.
“The carbon dioxide and methane emissions associated with blue hydrogen reduce the benefit of a hydrogen economy and lead to a climate penalty at high leakage rate or blue hydrogen share,” the study said. “The leakage rate and the hydrogen production pathways are key leverages to reach a clear climate benefit from a large-scale transition to a hydrogen economy.”