Written by on April 15, 2023

A twitter post claiming that water vapor causes global warming is false.

“Yes, but it produces 100x less hydrogen per dollar of cost than breaking down coal to get the hydrogen. Clean coal is now, as it has been for centuries the least costly way to produce clean energy. But using hydrogen produces water vapor which causes more global warming than co2,” states the claim.

Water vapor is the most abundant greenhouse gas in the atmosphere, that is by both volume and weight. As a result of its heat trapping ability, it plays a vital role in climate feedbacks. When there is an increase in the concentration of greenhouse gasses and global temperature rises, the amount of water vapor in the atmosphere also increases and this in turn amplifies the warming effect.

According to the ACS Climate Science, despite accounting for almost 60% of the greenhouse warming effect, water vapor is not responsible for controlling the earth’s temperature, but is rather controlled by the temperature.

The National Atmospheric and Space Administration states that a rise in the concentration of water vapor does not cause global warming, but is rather an outcome of it. It only magnifies the effects from other greenhouse gasses. NASA indicates that earth’s temperature increases as a rejoinder to the increase in the concentration of greenhouse gasses e.g., CO2, which in turn leads to an upward trajectory in evaporation from both land and water areas. Due to the fact that warmer air doesn’t easily condense and precipitate out of the atmosphere at higher temperatures, its concentration of water vapor rises since it holds more moisture. Heat radiated from earth is therefore absorbed by the water vapor, so as to obstruct it’s escape into the atmosphere. This is referred to by scientists as a “positive climate feedback loop.”

According to a research published on 27th September 2018, water vapor added at the present irrigation rates would produce a net Effective Radiative Forcing ERF of −0.1 to +0.05 W m−2 and the 100 year effective Global Warming Potential GWP for vapor emitted close to the surface is -0.001 to +0.0005, thus making emitted water a thousand times less effective per kilogram in altering the earth’s heat budget compared to CO2. The study also finds a top-of-atmosphere cooling instead of warming. This is due to the fact that the added water vapor rains out prior to reaching the required altitudes required to notably contribute to the earth’s greenhouse effect.

We looked into this claim stating that water vapor causes global warming and found it to be false.

This fact-check was produced by Sky 106.1 FM with support from Code for Africa’s PesaCheck,  International Fact-Checking Network, and African Fact Checking Alliance network.

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