How green is blue hydrogen

This article examines the lifecycle greenhouse gas emissions of blue hydrogen, accounting for carbon dioxide and unburned fugitive methane emissions. It found that, contrary to what many have claimed, blue hydrogen emits a considerable amount of greenhouse gas because fugitive methane emissions for blue hydrogen are higher than grey hydrogen due to the increased use of natural gas to power the carbon capture process. The article also finds that blue hydrogen's carbon footprint is even higher than just burning natural gas, coal, and diesel oil.   

Grey hydrogen is produced when heat and pressure convert the methane in natural gas into hydrogen and carbon dioxide, a process known as steam methane reforming (SMR). This process currently consumes 6% of the global natural gas supply and emits high levels of greenhouse gases. Grey hydrogen also differs from brown hydrogen, which is made from coal gasification. Blue hydrogen is proposed as an alternative. Blue hydrogen refers to hydrogen produced by SMR or coal gasification but with carbon dioxide capture and storage.  

Some have claimed blue hydrogen has low or zero emissions, but this claim is challenged because not all emissions can be captured. Carbon dioxide and methane can leak during the extraction and transportation of natural gas, and in the production of blue hydrogen.  

The article assumed a 3.5% methane emission (or leakage) rate from natural gas and a 20-year global warming potential for methane and found that the combined emissions of carbon dioxide and methane are greater for grey hydrogen and blue hydrogen than for the combustion of any other fossil fuels. This is because hydrogen production requires a large amount of natural gas per unit produced, with associated methane emissions. Relaxing the default assumption of the methane emission rate from natural gas and the global warming potential still yielded results showing that grey and blue hydrogen have greater emissions than the combustion of natural gas.   

The results of this article, which present an assumed best-case scenario for blue hydrogen, have significant implications for the future of hydrogen production. The assumption that the captured carbon dioxide can be stored indefinitely for decades and centuries into the future, while optimistic, is unproven. Therefore, this article makes a compelling case against blue hydrogen as a cleaner alternative to grey or brown hydrogen on climate grounds. It suggests that there is no real advantage of producing blue hydrogen using natural gas compared with simply using the natural gas directly for heat, indicating that there may be no role for blue hydrogen in a carbon-free world.   

Note: a comment piece by Romano et al. was published, countering some of the claims made in this paper. The comment piece points out that the method Howarth and Jacobson used in this paper to calculate the energy balance of blue hydrogen leads to an overestimation of CO2 emissions and natural gas consumption. It also points out that the leakage rate of natural gas assumed in this paper is at the higher end of the estimated emissions from current natural gas production in the US and cannot be considered representative of all natural gas and blue hydrogen globally.