Fig. 3: Climate impacts of hydrogen applications compared with two scenarios: business as usual and low carbon.

a, Ammonia. b, Biofuels. 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. Violin plots show the full distribution of results (kernel density estimation). The width of each violin represents the frequency of values; the white line marks the median, and the thicker bar the interquartile range (IQR). The thin line indicates the remainder of the distribution, defined as the range from Q1 − 1.5 IQR to Q3 + 1.5 IQR. Data points outside this range are considered outliers. Sample size (n), representing the number of times hydrogen is supplied in considered hydrogen projects, is shown for each distribution. The y axis in the violin plots shows the climate impact of the application of hydrogen for specific purposes per application-specific functional unit up to 2043, while the x axis illustrates the distribution of (non-weighted) results: the wider the area, the more facilities exhibit a specific amount of climate impacts. Red and green horizontal lines in each plot indicate the means of the business-as-usual scenario (fossil-fuel-based application) and a low-carbon scenario regarding climate impacts of reference processes. The diamond markers in the violin plots illustrate the climate impact if very low-carbon hydrogen is sourced from water electrolysis using nuclear power within a decarbonized global economy in 2040.