# Hydrogen > In the near term $\text{H}_2$ production from fossil fuels will remain the most cost-competitive option in most cases. > *The Future of Hydrogen, 2018, IEA.* ## Hydrogen Colours ### Brown Hydrogen Brown hydrogen refers to hydrogen produced from coal through gasification processes. This method, similar to grey hydrogen, releases significant amounts of carbon dioxide into the atmosphere, contributing to environmental degradation. Brown hydrogen is less environmentally friendly than green and blue hydrogen, as it relies on fossil fuels and lacks the emission reduction measures implemented in blue hydrogen production. ### Grey Hydrogen Grey hydrogen, currently the most prevalent form (~70% worldwide production), is produced through steam methane reforming (SMR) or partial oxidation of natural gas. This process emits carbon dioxide as a byproduct, making it a major contributor to greenhouse gas emissions. While grey hydrogen is widely used in various industries, its environmental impact has spurred efforts to transition to cleaner alternatives. The need for carbon reduction has prompted exploration of greener hydrogen production methods, such as electrolysis and carbon capture technologies. Footprint: 9 - 13 $\text{kg}_{\text{CO}_2}\text{/kg}_{\text{H}_2}$ ([[Carbon Capture and Storage#Carbon emission scope types|scope 1]] emissions only) ### Blue Hydrogen Blue hydrogen is an intermediate step towards cleaner hydrogen production. Similar to grey hydrogen, it is derived from natural gas through steam methane reforming (SMR) or partial oxidation. The distinguishing factor is the incorporation of carbon capture and storage ([[Carbon Capture and Storage|CCS]]) technology, which captures and stores the carbon emissions, significantly reducing the overall environmental impact. Blue hydrogen offers a compromise between the established infrastructure of grey hydrogen and the sustainability goals of green hydrogen, providing a lower-emission alternative for industries while transitioning to cleaner energy sources. Footprint: 0.4 - 4.0 $\text{kg}_{\text{CO}_2}\text{/kg}_{\text{H}_2}$ ([[Carbon Capture and Storage#Carbon emission scope types|scope 1,2&3]] emissions) Blue Hydrogen must achieve low carbon levels defined differently around the world e.g. - UK LCHS (Low Carbon Hydrogen Standard) $\text{CO}_2$ emissions must be $\text{<20 g CO}_2e/\text{MJ}_{\text{LHV}}\text{H}_2$ (approx. $\text{2.4 kg CO}_2e/\text{kg}\text{H}_2$) - US [[Inflation Reduction Act|IRA]] 45V is a tiered system where the highest subsidy is offered for $\text{CO}_2$ emissions $\text{<0.45 kg CO}_2e/\text{kg}\text{H}_2$ ### Green Hydrogen Green hydrogen is heralded as the cleanest form, produced through water electrolysis powered by renewable energy sources like wind or solar. Water is split into hydrogen and oxygen, with the process emitting only water vapour. As a zero-emission energy carrier, green hydrogen plays a pivotal role in decarbonising various sectors, including transportation and industry. Its potential to store renewable energy and its versatility make it a key player in sustainable energy transitions worldwide, aligning with global efforts to mitigate climate change and reduce dependency on fossil fuels. Footprint: 0 $\text{kg}_{\text{CO}_2}\text{/kg}_{\text{H}_2}$ with dedicated renewable power supply.