What would be the c limate effects of a complete conversion to hydrogen powered cars?

Question

I want to know if anyone has modeled this scenario. And please educate me if I have some fundamental misunderstandings about any of this. But less just say that tomorrow, all cars suddenly were converted to hydrogen powered cars emitting nothing but water as exhaust. What would the climatological effects be of introducing all that water into the atmosphere? My gut tells me that there would be fairly significant effects related to weather, water levels, ozone, whatever.

I have asked this question before and been called a left wing, environmentalist cook. I have no political agenda in asking this. I just want a thoughtful answer and some references to facts and data related to this topic.

Answer 1

Hydrogen is not an energy source (primary energy). It is an energy carrier (secondary energy) just like electricity and HAS TO BE PRODUCED.

Fuel cells which can use hydrogen have a higher efficiency than regular reciprocical engines... nevertheless, the conversion from oil or another source to hydrogen is not very efficient and is expensive.

Therefore, you just DISPLACE the energy consumption to other parts of the chain.


I just give you an example: H2 can be easily produced with methane (CH4)... and the efficiency of the conversion is 70%. Then your fuel cell has also 70% efficiency. This means globally you have a 50% efficiency compared to the 40% of the diesel motor.
You also used an expensive and very clean fuel (methane) which you could have burned directly.
What remains of the reaction is pure carbon... which I guess you are also going to burn. Well so on the CO2 balance, there is no difference.

Answer 2

If the hydrogen is produced by electrolysis of water, and the electrolyzers are powered by nuclear energy, then yes there would be a huge effect on CO2 emissions. If the hydrogen were made from a hydrocarbon such as natural gas, the effect would be significant but not nearly as good as eliminating ALL the carbon.

To put a number on it, globally about 18% of all carbon dioxide emissions come from road transportation. (the percentafge is somewhat higher in the US) So, hydrogen cars + nuclear electrolysis could cut carbon emissions by up to 18%. This would a be a huge step in at least maintaining the current levels of CO2 concentration in the atmosphere, and eventually reducing them. Additional reductions in the industrial and power generation sectors (more nuclear!) could also be needed as energy usage expands.

What does this degree of reduction actually do to the climate? Nobody really knows. We are at about 350 ppm (parts per million) CO2 right now, and could rise to 400-500 ppm by 2050 if we do nothing. It's predicted that global temperatures will rise a few degrees if this happens. A 25% reduction in emissions across the board might be enough to hold the line at 350 ppm.

Don't worry about the water in the exhaust. People often forget that the primary product of combustion of gasoline is also water, it's just that gasoline makes a lot of other products as well. Gasoline is has carbon and hydrogen in it: the carbon makes CO2 and the hydrogen makes H2O. Hydrogen vehicles do not make that much more water.

Answer 3

Depends mostly on how you make the hydrogen.

Lets assume it's by nuclear power.

The reduction in CO2 would be very beneficial.

The increase in water vapor would be inconsequential.

There's a natural "water cycle" which reacts rapidly to keep things under control (unlike the carbon cycle which is much slower to react). Pump water vapor into the air, get more clouds and rain. Relatively little effect on global warming.

The main effect of water vapor is to amplify CO2 based warming. Warmer air can hold more water vapor, and there is more greenhouse effect from the water vapor.

Much more detail about this here:

http://www.realclimate.org/index.php?p=142

It's a good idea, if we make the hydrogen right.

Answer 4

First we need to look at the hydrogen with air will produce NO2 as it burns the Nitrogen. Hydrogen is very hot so it would make a lot of NO2. The only solution to that would be to use liquid oxygen and liquid hydrogen and that would hot enough to melt your motor.
There is another problem with your C foot print as GOD put plants here to reprocess our air and if we produce no CO2 all the plants will die ,and that means we will too.

Answer 5

Wet streets and higher costs. The hydrogen car has a very long way to go before it can replace the gasoline engine.A better scenario would be the feasibility of solar/battery cars.

Answer 6

We currently get hydrogen from crude oil or natural gas, so you energy souce hasn't changes from fossil fuel. You can't produce it from water unless you use as much energy as you will get out of burning it (actually you use more).

Answer 7

Nothing for about 100 years. That is about how long it takes CO2 to be completely eliminated from the atmosphere. It WILL stop one of the causal factors of Global Warming, but it won't immediately stop the symptoms.

But at least in the meantime it won't make things worse!

Answer 8

Where would you get the hydrogen? You have to use more energy to produce the hydrogen than the hydrogen will produce. Right now that energy would come primarily from fossil fuels. Of course fossil fuels aren't affecting the climate.

Answer 9

The same as it is now except more humid. ie Florida heat vs Arizona heat.