Wouldn’t the water vapor released from tens of millions of fuel cell powered vehicles create massive amounts of humidity to the point that in 50 years the whole earth will be covered in a massive humidity blanket which could raise temperatures and destroy ecosystems
No. Zero impact. H2 and O2 turns to H2O when burned. Water condenses and makes water vapor combines with all other water vapor from normal evaporation of the oceans.
The impact would be enormous.
The energy required to replace all existing vehicles with new freshly manufactured or modified vehicles and the energy required to fabricate a distribution network would have a carbon footprint that will likely never be amortized as there are so many better options than hydrogen.
For one, synthetic fuels can be made from hydrogen and carbon monoxide via the Fischer Tropsch reaction. This is what fueled WWII Germany, embargoed South Africa and is the US Airforce’s backup fueling plan. Although coal gasification has been the source of hydrogen and carbon monoxide in the past, biomass can be gasified and Sandia Labs has made them directly from CO2 and H2O with Solar Power.
Synthetic fuels being virtually pure iso-octane for synthetic gasoline and virtually pure iso-dodecane for synthetic diesel would not require vehicles to be modified or replaced and would work with the current distribution network. Of course, the automobile industry wants to push hydrogen due to the prospects of obsoleting everything on the road and hence generating an incredible increase in demand for product but the initial environmental costs of deploying hydrogen technology is unconscionable.
Actually the water emissions from HFC cars wouldn’t be much of a problem. In the grand scheme of things it’s just a drop in the bucket (forgive the pun) compared to the evaporation from the oceans. Even with 10 million cars on the road. Remember 75% of the earth’s surface is water.
The problem with hydrogen fuel cells is making the fuel. Only laboratory grade hydrogen can be used. While the oil refining industry has a lot of hydrogen, it can’t be used because of contaminates like carbon. So the next best way to get the hydrogen is to split water with electrolyses. On a per mile basis this process uses 4 to 5 times the electricity a simple battery electric car does. As a side note: HFC cars only last 30,000 miles. Carbon clogs the cells and since the cars get the oxygen from the air which has carbon dioxide in it your guaranteed to clog the cells quickly.
Now for the part your really interested in, pollution. If a battery electric car uses 100% coal generated electricity it’s per mile pollution is about half of gas powered car. Now since a HFC car uses 4 times the electricity and is powered by that same coal generator plant it will produce 2 times the pollution of gas car per mile.
There is one bright spot in that more and more renewable energy is being added to the grid every day in the form of solar and wind power.
We would have to rip up a good chunk of the earth to find enough platinum catalyst to make all those fuel cells.