Fig. 4: Boxplots showing the potential emission reductions for all hydrogen projects associated with the specific application, compared with business-as-usual and low-carbon scenarios.

a, Ammonia. b, Biofuels (note the broken y axis). c, Methane. d, Methane mobility. e, CHP. f, Domestic heat. g, High-temperature industrial heat. h, Hydrogen. i, Iron and steel. j, Methanol. k, Mobility. l, Power. m, Refining. n, Synfuels. In the boxplots, the horizontal line inside the box represents the median. The box itself spans the IQR, capturing the central 50% of the data, with its lower and upper edges corresponding to the first (25th percentile) and third quartiles (75th percentile). The whiskers extend up to 1.5 times the IQR from these quartiles. The black circles represent outliers, that is, individual hydrogen projects with substantially lower or higher emission reduction potential. Sample size (n), representing the number of times hydrogen is supplied in considered hydrogen projects, is shown for each distribution. The subplots have shared primary y axes (except for the different y-axis scale for biofuels). The y axis illustrates the emission reduction potential per specific amount of hydrogen used in the application. The x axis illustrates the results based on two reference scenarios. The mean values of the emission reduction potentials for both reference scenarios are provided in each panel; positive values represent emission reduction potential per specific amount of hydrogen used, while negative values represent GHG emissions higher than the reference. n.a., not applicable.