By Steven Hamburg and Ilissa Ocko
Oil and gas companies and governments worldwide are increasingly looking to hydrogen as their pathway to decarbonization. Over 350 new projects worth $500 billion have been recently announced, according to the Hydrogen Council. The International Energy Agency says demand could increase sixfold by 2050.
Before committing to this vast buildout, it is essential to understand how hydrogen can contribute to climate change — including hydrogen’s own significant warming potential, which remains widely overlooked.
Digging into the science of hydrogen
We set out to assess the current science in a paper now in peer review, and find that under the right circumstances, hydrogen could indeed be part of a clean energy transition. But done wrong, it could be worse for the near-term climate than the fossil fuels it would replace.
While carbon dioxide can be a byproduct of hydrogen production, hydrogen itself emits no carbon dioxide when burned or used in a fuel cell. But when emitted into the atmosphere, hydrogen contributes to climate change by increasing the amounts of other greenhouse gases such as methane, ozone and water vapor, resulting in indirect warming.
That’s a problem because hydrogen’s small molecule is difficult to contain. It is known to easily leak into the atmosphere throughout the value chain. The farther it travels between production and end-use the greater the potential for leakage.
That much is well understood. But it turns out we know very little about how much hydrogen actually escapes from real-world systems. It hasn’t been clear because there has been no reason to look beyond basic safety thresholds — until now.
This is because traditional metrics systematically ignore the near-term impact of hydrogen and other short-lived climate-forcing agents by expressing the warming effects from a one-time pulse of emissions over a 100-year timeframe (GWP-100), masking a much bigger, more immediate influence.
There is another reason the warming effects of hydrogen have been underestimated. Until recently, every estimate of hydrogen’s climate-forcing power considered only the troposphere and not effects in the stratosphere. Accounting for both reveals that hydrogen has greater warming potential than is typically recognized.
Applying the combined atmospheric effects over a shorter, more relevant timeframe, we estimate the five-year warming power from a pulse of hydrogen relative to CO2 is 20 times greater than current calculations show using the standard 100-year approach.
And when we look at the relative warming impact from continuous instead of pulse emissions — which are more representative of the real world — hydrogen is 100X more potent than CO2 emissions over a 10-year period.
The importance of assessing leak rates
To understand what this could mean, we considered possible leak rates suggested in the literature.
In high leakage situations, hydrogen emissions could yield nearly twice as much warming in the first five years after replacing its fossil fuel counterparts. But if leak rates are minimal, hydrogen could yield an 80% decrease in warming during that same time period.
CO2 emissions avoided over decades by substituting hydrogen means that climate benefits accrue regardless of leak rates. Even with high leakage, the warming effect 100 years after a hydrogen switch would be 80% lower compared to fossil fuels (although relying on pulse, rather than continuous emissions, significantly inflates that benefit).
These findings hold true for hydrogen produced with renewable energy: With even moderate leakage, this ‘green’ hydrogen could increase near-term warming. The impacts are even greater for ‘blue’ hydrogen produced from natural gas, due to added warming from the methane emissions along the natural gas supply chain.
This means that in hydrogen-intensive scenarios (50% or more of final energy demand supplied by hydrogen) with high leak rates, even green hydrogen could contribute a tenth of a degree Celsius of warming in 2050.
Since the near- and mid-term warming impacts of hydrogen are so much higher than usually recognized, it makes sense for the impacts to be explicitly reflected and actively minimized in order to achieve the maximum climate benefits of replacing fossil fuels with hydrogen. After all, it is much easier to minimize hydrogen leakage when designing a system versus retrofitting one.
Getting hydrogen right, from the start
Here are five things to help ensure a positive climate outcome:
- Conduct more research on hydrogen’s warming effects relative to other greenhouse gases and develop models that can increase confidence in the impacts hydrogen deployment would have on global temperatures at varying leakage rates.
- Accurately measure leakage, which will require equipment capable of measuring hydrogen concentrations at the parts-per-billion level, so we can systematically quantify leakage rates.
- Use climate metrics that reflect the role that hydrogen leakage could play over the policy-relevant near-term, instead of relying exclusively on 100-year accounting.
- Include the likelihood of hydrogen leakage and its impacts in decisions about where and how to deploy hydrogen. Use should be concentrated where it is produced and used in close proximity, with limited need to transport it.
- Identify leakage mitigation measures and best practices. Lessons learned over the past decade about minimizing natural gas leakage can help, despite the differences in the properties of these two gases.
Diversion of renewably generated electricity to produce green hydrogen is also a concern. Because hydrogen does not occur on its own, immense energy is needed to extract it from water or other molecules. This means more energy is needed to use hydrogen than in cases where direct electrification is possible.
We must also better understand additional climate and environmental questions, including the health effects on local communities of NOx emissions from combusting hydrogen and the impact on water resources.
Nor can we forget to consider the efficiency and permanence of carbon-capture technology necessary for producing hydrogen from natural gas, and minimizing methane leakage. Preventing these emissions is essential for blue hydrogen to deliver large net climate benefits.
The industry is still in its infancy. We have an opportunity to ensure the enormous investment in hydrogen projects worldwide delivers the benefits that its backers promise — but only if we take a proactive and scientific approach in how, when and where we adopt it.
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