New York, Aug 15 : "Blue" hydrogen -- an energy source that involves a process for making hydrogen by using methane in natural gas -- is being lauded as a clean, green energy to help reduce global warming. But researchers believe it may harm the climate more than burning fossil fuels. The carbon footprint to create blue hydrogen is more than 20 per cent greater than using either natural gas or coal directly for heat, or about 60 per cent greater than using diesel oil for heat, according to new research published in the journal Energy Science and Engineering. Blue hydrogen starts with converting methane to hydrogen and carbon dioxide (CO2) by using heat, steam and pressure, or gray hydrogen, but goes further to capture some of the CO2. Once the byproduct CO2 and the other impurities are sequestered, it becomes blue hydrogen, according to the US Department of Energy. The process to make blue hydrogen takes a large amount of energy, which is generally provided by burning more natural gas, according to the researchers from the Universities of Cornell and Stanford. "In the past, no effort was made to capture the CO2 byproduct of gray hydrogen, and the greenhouse gas emissions have been huge," said Robert Howarth, professor of ecology and environmental biology at Cornell. "Now the industry promotes blue hydrogen as a solution, an approach that still uses the methane from natural gas, while attempting to capture the byproduct CO2. Unfortunately, emissions remain very large," he added. Methane is a powerful greenhouse gas, Howarth said. It is more than 100 times stronger as an atmospheric warming agent than CO2 when first emitted. The recent United Nations' Intergovernmental Panel on Climate Change report shows that cumulatively to date over the past century, methane has contributed about two-thirds as much to global warming as CO2 has, he said. Emissions of blue hydrogen are less than for gray hydrogen, but only by about 9 per cent to 12 per cent. Blue hydrogen as a strategy only works to the extent it is possible to store CO2 long-term indefinitely into the future without leakage back to the atmosphere. On the other hand, an ecologically friendly "green" hydrogen does exist, but it remains a small sector and it has not been commercially realised. Green hydrogen is achieved when water goes through electrolysis (with electricity supplied by solar, wind or hydroelectric power) and the water is separated into hydrogen and oxygen. /IANS