What are the ecological ramifications of turning seawater into hydrogen? Are we depleting the total amount of water on the planet? I realize the scale that it’s happening at is probably relatively small, but I’m curious.
I suspect that's what people thought when they began burning oil and gas for energy...
I don't remember the source, nor can I vouch for the veracity, but I remember reading an article that worked out what would happen if all cars ran on hydrogen. IIRC it had a significant impact on local weather conditions in cities.
3/4th of the earth surface is covered by water. Total oil mining since 1850s is estimated between 100-150 billion metric tons.
If you pump out 150 billion metric tons of sea water from the oceans the sea level will drop 0.5mm (1/50th of an inch).
Moisture levels will increase and water vapor is also a greenhouse gas. Everything is a compromise...
In 2019 the UK used 46.5 billion litres of hydrocarbon road fuel [0]. Let's say it all has diesel's energy density of 36.9 MJ/litre. That's 1.71585e+18 joules per year total.
Let's pretend fuel use per capita is constant across the country. On 2018 numbers, London's 8.9 million people [4] out of the UK's 66.44 [5] gives it about 13% of the total, so 2.299e+17 joules.
If you get 286kJ from burning one mole of hydrogen gas, London would have to burn 803 gigamoles per year, making the same quantity of water in the process. If water weighs 18.0153 g/mol [3], that's 14.478 million tonnes of water per year. If that all fell as rain, then assuming water weighs a tonne per cubic metre, spread out over London's 1,737.9 km2 [4], that would be an extra 0.0228 mm of rain per day.
In July, Greenwich sees an average of 1.1 mm of rain per day [6], so that's on the order of 2% extra rainfall.
This calculation is extremely approximate, and i have neglected to account for a the water from the combustion of hydrocarbon fuels. Rain is not the only way water gets involved in weather - i'm not sure how to estimate the effect on humidity, for example. And the effect will be bigger for denser and drier cities (Dubai!).
It would be interesting to see a proper analysis of this.
