TABLE OF CONTENTS


This article gives an overview of hydrogen and explains how to simulate the growth of hydrogen in En-ROADS, as well as its impact on greenhouse gas emissions and the climate.  
 

What is hydrogen?

Hydrogen (H2) is a molecule made of two hydrogen atoms. It has the highest energy content per unit of mass of any common fuel, but a very low energy density per unit of volume—requiring it to be compressed or liquefied for storage and transport. Hydrogen exists naturally in very small amounts (often called “white hydrogen”) in the atmosphere and in certain geological formations. However, nearly all the hydrogen used today is produced through industrial processes from other primary energy sources—such as fossil fuels, wind and solar, and biomass—making it an energy carrier rather than a primary source of energy. 


How is hydrogen produced?

Today, the most common method for producing hydrogen is steam-methane reforming, which extracts hydrogen from natural gas using steam. A cleaner alternative is “green hydrogen,” produced via water electrolysis, a process that uses electricity to split water into hydrogen and oxygen. This method is becoming more technically feasible, and when powered with renewable energy, avoids the production of greenhouse gases.



Does hydrogen create pollution?

When burned for heat and electricity, most fuels produce pollutant by-products, such as particulate matter, carbon monoxide, and carbon dioxide. Hydrogen, in contrast, produces mostly water as a by-product. How “clean” hydrogen is will depend on the production path used. When it is produced from low-carbon electricity and water, it could be a solution to reducing carbon emissions. On the other hand, producing hydrogen from fossil fuels releases greenhouse gases.


In addition, while hydrogen itself is not a greenhouse gas, it can indirectly contribute to global warming. When leaked into the atmosphere, hydrogen interferes with the chemical processes that break down methane, effectively extending methane’s lifetime and enhancing its warming impact. Hydrogen can also produce polluting nitrogen oxides (NOx) due to reactions with nitrogen in the air. 


What are the applications of hydrogen in energy decarbonization?

Many experts claim that hydrogen (H2) will play a major role in the clean energy transition, and a global “hydrogen economy” has gained what the IEA describes as “unprecedented political and business momentum.” En-ROADS allows users to explore hydrogen growth scenarios—testing the relative costs, market potential, and climate benefits of hydrogen across different sectors. 


Today, nearly all hydrogen is produced from fossil fuels and used as a feedstock in industrial processes such as ammonia production for fertilizer, oil refining, and methanol manufacturing. This so-called gray and brown hydrogen (see color definitions below) contributes significantly to emissions. 


Looking ahead, hydrogen produced from renewable energy (green hydrogen) or other lower carbon sources is often proposed as a complement to electrification in areas where electrifying directly is difficult or expensive. These areas include: 


  • Industry - energy and feedstocks: Using green hydrogen to replace natural gas in boilers and other settings where high heat is needed or as feedstocks in chemical processes, such as separating iron from iron ore 

  • Transport: Converting hydrogen into synthetic fuels (e.g., ammonia, methanol) for aviation and shipping 

  • Buildings: Burning hydrogen in boilers for heating in residential and commercial spaces

  • Electricity: Producing green hydrogen using excess renewable electricity to be stored over long durations and later converted to electricity


What are the types of hydrogen production simulated in En-ROADS?

Hydrogen can be produced from a range of energy sources using approaches like steam methane reforming, gasification, and electrolysis, and as a result, has a different carbon intensity. In En-ROADS, hydrogen production pathways are color-coded by energy source, consistent with the terminology used by the industry.



Here are the types of hydrogen by production pathway or “color” included in En-ROADS:

  • Brown hydrogen is produced with coal or biomass via gasification and produces CO2 as a byproduct 

  • Gray hydrogen is produced with natural gas via steam methane reforming (SMR) and produces CO2 as a byproduct 

  • Blue hydrogen is produced from natural gas, coal, or biomass, with carbon capture and storage (CCS) to reduce emissions 

  • Yellow hydrogen is produced with electricity from the grid via electrolysis of water and its CO2 emissions depend on how much the grid uses CO2-emitting sources 

  • Pink hydrogen is produced with dedicated nuclear electricity via electrolysis of water, resulting in no direct CO2 emissions 

  • Green hydrogen is produced with dedicated wind and solar electricity via electrolysis of water, resulting in no direct CO2 emissions 

All of these processes involve significant losses of energy during production, which means hydrogen is a relatively inefficient and expensive energy carrier compared with the direct use of fuels or electricity. 


Note: There are other speculative sources of hydrogen, such as geological reserves of naturally occurring “white” hydrogen found under mountain ranges that are not included in En-ROADS at this time.


What is the current status of the hydrogen economy?

To see the current status of hydrogen in En-ROADS, use the Baseline Scenario and look at the graphs (both under Graphs > Final Energy Consumption—Totals): 

  1. “Hydrogen Production by Color”
  2. “Hydrogen Production by Use”

Global hydrogen demand in 2024 was about 100 million tons (IEA, 2025). In energy terms, this is equivalent to 12 exajoules per year. At present, this hydrogen is almost entirely produced via carbon-intensive methods (see the gray and brown wedges in the left graph above) and used as an industrial feedstock (see the graph to the right above) in producing ammonia (NH3) for fertilizers, in refining (desulphurising) crude oil, and as a chemical agent in iron ore reduction. 


Note: En-ROADS requires users to introduce policies in order to simulate the growth of hydrogen in other sectors. Read below for more information. 


Hydrogen features in En-ROADS


This section highlights where hydrogen appears in En-ROADS and how to explore its role across various sectors.


Note: As of April 2026, the hydrogen model is being updated. These changes will significantly affect system behavior and results. Please revisit this explainer once the update is released.



Scenarios to test:

  1. Simulate a breakthrough in hydrogen storage: Use the “Hydrogen storage breakthrough cost reduction” slider (found in the Renewables advanced view) within a scenario featuring high shares of variable renewables, such as in this scenario. Hydrogen storage only scales when wind and solar dominate the electricity supply, creating a demand for long-duration energy storage. You can drive this demand by: 
    • Increasing renewable subsidies; 
    • Adding a carbon price; 
    • Removing fossil fuel subsidies; or 
    • Increasing taxes on fossil fuels. 

  2. Simulate hydrogen growth in air and water transport: Navigate to the advanced view for Transport Electrification and use the “Hydrogen subsidy and fueling infrastructure” slider. This simulates growth in these hard-to-electrify sectors. Scenario link.

  3. Simulate hydrogen growth in buildings and industry: Navigate to the advanced view for Buildings and Industry Electrification and use the “Hydrogen buildings subsidy and infrastructure” and “Hydrogen industry subsidy and infrastructure” sliders. Note: The Buildings and Industry sector in En-ROADS is being updated. To see meaningful hydrogen growth in the current model version, pair these subsidies with a “Fuel-powered equipment sales limit,” located in the same advanced view. Scenario link.

  4. Simulate the use of dedicated renewable energy to produce green hydrogen: Use the “Hydrogen storage breakthrough cost reduction” slider (found in the Renewables advanced view). Scenario link.



Hydrogen graphs to explore:

  • Hydrogen Production by Color—Area
  • Hydrogen Production by Use—Area 
  • Price of Hydrogen 
  • Renewables Capacity for Hydrogen Production 
  • Cost Ratio of Hydrogen Equipment to Alternatives