Climate impact of hydrogen could be much bigger than estimated: Study

‘Clean’ hydrogen deployment can be considerably better or worse for the climate than the fossil fuel technologies they are replacing, says a new study

According to new research by scientists at the Environmental Defense Fund, standard frameworks used to assess the climate impacts of hydrogen production are vulnerable to broad miscalculation. The research found that climate impacts of hydrogen and methane emissions can considerably reduce the climate benefits across  key hydrogen use cases and timescales. As governments, investors, and industry look to hydrogen to help meet climate goals, the researchers said it is critical to get this accounting right. 

Published in the journal Environmental Science & Technology, the study showed that the most widely used hydrogen life cycle assessment frameworks fail to include three critical factors: the warming effects of hydrogen emissions, measured real-world methane emissions intensities, and the near-term warming impacts of emissions. 

Possible implications of deploying hydrogen

To understand the potential impacts of hydrogen deployment, the researchers reanalysed a previous lifecycle assessment of hydrogen. They found that when these factors are included, hydrogen systems could be considerably better or worse for the climate than the fossil fuel technologies they are replacing. 

If hydrogen and upstream methane emissions are high, blue hydrogen pathways (natural gas with carbon capture) could actually increase near-term warming by up to 50% compared to fossil fuels. By contrast, if those emissions are low, it could decrease warming impacts by over 70%. For green hydrogen pathways (renewable-based electrolysis), high hydrogen emissions can reduce the climate benefits in the near-term by up to 25%. 

“It’s important to get the emissions accounting right, both to accurately assess climate impacts of hydrogen systems and to identify opportunities to reduce them,” said EDF climate scientist and lead author Tianyi Sun. “When we consider all climate warming emissions and their impacts over the near- and long-term, our analysis shows that hydrogen deployment can have far greater impacts than expected.” 

Carbon capture and access to renewable energy 

It is often assumed that green hydrogen production utilizes excess or new renewable resources and does not influence the rate of decarbonization of the electric grid. However, given the large gap between availability of and demand for zero-carbon electricity, there is concern that green electrons could be diverted from decarbonizing the power grid. If this occurs, then the resulting gap would need to come from natural gas or coal-fired power plants, leading to increased greenhouse gas emissions.

The analysis also demonstrated how other factors such as lack of renewable electricity resources or insufficient carbon capture rates could further reduce anticipated climate benefits of hydrogen deployment. Consistent with other studies, the analysis found that adding renewable electricity to local systems is necessary to help ensure the climate benefits of green hydrogen development. Otherwise, renewable electricity used to produce green hydrogen is likely replaced by natural gas or coal, resulting in full elimination of intended climate benefits to 3 times increase in emissions at the system level.

With respect to carbon capture rates for blue hydrogen, the previous assessment uses 98%, a rate which has not yet been consistently achieved. When applying a lower rate of 60%, the climate benefits of blue hydrogen pathways are reduced by 15-50% in the near-term, and 20-60% in the long-term.

“As we build out the hydrogen economy, we have a very real opportunity to ensure the enormous investments in hydrogen projects worldwide yield the climate benefits being sought – and avoid unintended climate consequences. We need robust assessment methods and data to ensure the potential is achieved in practice,” said Ilissa Ocko, EDF Senior Climate Scientist.

Assessing climate impacts of hydrogen

The report said the standard metric employed for assessing climate impacts [Global Warming Potential (GWP) with a 100-year time horizon] does not convey warming effects in the near-term and assumes an unrealistic one-time pulse of emissions rather than continuous emissions over time.

GWP is used to combine emissions of multiple GHGs by converting non-carbon dioxide climate pollutant emissions to their carbon dioxide ‘equivalent’ based on radiative properties and atmospheric lifetimes. 

Also, the analysis mentioned that the addition of hydrogen emissions and varying levels of representative methane emissions shows that the climate benefits of battery electric vehicles (BEVs) are considerably larger than blue hydrogen light duty vehicles (LDV). 

Overall, concluded the analysis, the cumulative warming impact from constant emissions of switching from fossil fuel technologies to blue or green hydrogen alternatives depends on the specific application, production method, the hydrogen and methane emissions rates, and the timescale of interest. The relative impact across all timescales (under 2050 conditions) ranges from a 93% reduction in warming to a 46% increase in warming (considering extreme cases) — meaning either a near elimination of fossil fuel technologies’ warming impacts or even more warming from the hydrogen technologies. The results under 2030 conditions are similar. 

“Important decisions are being made about future clean energy systems, with implications for decades to come,” said Steven Hamburg, EDF chief scientist. Hydrogen can be an effective decarbonization tool in many cases, but only if we ensure that its climate impacts are kept to a minimum. This requires upping our game on emissions accounting of climate impacting gases including hydrogen itself.”  

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