Climate change: ‘Clear and unequivocal’ emergency, say 11,000 scientists.

The problem is that everything we do continues to add CO2 to the atmosphere the only things that remove that CO2 are life and processes that fix the carbon in rocks like limestone, as long as the net annual production of CO2 is greater than the amount that gets taken out of the system by living organisms and chemical processes we are making the problem worse, there are several future tipping points one of the big ones is the methane trapped in permafrost, at some point average temperatures will grow high enough to cause the release of that methane and when that happens it's pretty much over.

So no I don't think we will get away with a percentage reduction, more CO2 equals a greater greenhouse, right now we are being helped by a period of lower solar activity which is reducing the energy input to the planet by a very small but significant amount, that will change the sun will become more active again in 40 or 50 years time.

Makes no difference if it is hydrogen or electric, the problem is the energy required to make the fuel, 95% of the hydrogen for cars is made from natural gas, so you still have the problem of what to do with the carbon. (edit: actually 95% of all hydrogen we use is made from natural gas)

Hydrogen would be a good fuel because you can either put it through fuel cells to generate electricity or you can burn it directly completely cleanly, it is likely more energy dense than lithium ion batteries so you should probably get greater range in a vehicle and that makes it attractive, plus refuelling would be fast, but you still have to deal with where the hydrogen comes from.

In an ideal world you would create the hydrogen by electrolysis using electricity generated by renewables, solar, wind and so on, but today you have to rely on pyrolysis to break down natural gas and that is energy intensive in its own right. (edit: I forgot to add the energy cost of cooling and or the compression required to transport the hydrogen as well).

Electric vehicles make sense because even though we still have to burn fossil fuels in a power station the process in the power station is more efficient than the process of burning the fuel in a car engine and the pollutants are more easily controlled in a centralised power plant although we are not really doing much about that but we could.

Most solutions that involve continued use of fossil fuels become less efficient at generating energy because you have to spend a lot of the energy generated to make the process clean, for example capturing the CO2 and turning it into limestone, that takes energy and all of the cleanup technologies that exist are generally not implemented because they will cost too much, when the accountants are doing the costing they don't factor in the cost of an unliveable planet so things like coal and oil and the likes are claimed to be cheaper and wind and solar are deemed to be expensive when in reality if you adjusted for the environmental impact of fossil fuels solar, wind and the likes would be dirt cheap.

The electricity used to split the water is what is actually propelling your car, the hydrogen is just a battery, a buffer, a way to store that power, and of course some energy is lost in the electrolysis nothing is 100% efficient.

Each Hydrogen atom has a single valence electron, Oxygen has an electronic configuration of (2, 6) which means it has 2 electrons in the inner shell and 6 electrons out of a stable configuration of 8 in its outer shell, therefore 2 hydrogen atoms with a valence of 1 can fill those configuration spaces in the outer shell forming a stable electronic configuration, the resulting compound is water.

When you split water both hydrogen and oxygen are generated, you don't get the exact same amount of energy back when you burn the hydrogen later but you do get a lot of energy back good enough to run a car.

You can also put hydrogen and oxygen through a fuel cell and burn it in a different way a way that is not explosive and which directly generates electricity, a fuel cell is special type of battery where the fuel is hydrogen from a tank and oxygen from the air it is very efficient compared to an internal combustion engine the only reason to burn hydrogen in an internal combustion engine is that we are very good at making that type of engine right now but fuel cells with electric motors would be a far better use of hydrogen.

edit: I suppose you could think of a fuel cell as backwards electrolysis

Also electrolysis would be fine as long as the power for the electrolysis was generated from renewables, there's not a lot of point in burning coal to generate electricity to split water to provide hydrogen for cars that can run cleanly unless you can do something about the waste products of the coal namely the CO2.

As a compressed gas, it is extremely hard and expensive in energy terms to cryogenically liquify hydrogen and it's not very energy dense even once it is liquified. (edit: it liquifies at around minus 253 degrees centigrade)

People are investigating various chemical storage mechanisms as well but the issue is the efficiency of reversing the storage, regenerating the hydrogen.

Anything that generates electricity could be used to electrolyse the water, so solar wind or hydro power could do it, the problem is that you need incredibly large amounts of energy to replace the energy that we use for transport, to put it in perspective vehicular transport of all kinds here in the UK uses more total energy than all the power stations and all the renewable power generation of the entire UK.

That means that even if all current power generation in the UK were converted to renewable sources we would still only have half the power we need to keep doing the things we do today as a result of oil.

Additionally it costs just over 2% of the energy content of the hydrogen just to compress it.

One extra point Malcolm, to extend the battery analogy that I used for hydrogen produced by electrolysis, all the fossil fuel energy we use in today's world is solar power, millions of years of solar power that powered life over the last couple of hundred million years.

All that oil and coal is life that lived and died on earth ancient photosynthesis that captured the light from our star the sun and used that light to fix carbon into organic materials which then decayed and were buried and over millions of years compressed into oil and coal.

History gifted us a huge battery.

And we are spending that resource at a furious pace in the space of a couple of hundred years, the earth took millions of years to lock away all that energy and we have to find ways to replace all of that in real time.

The sun provides 120,000 Terawatts (TW) of energy (flow) to Earth every day only a tiny fraction of that ever made it into coal and oil, I mentioned elsewhere that we use about 15TW continuously we need to capture about an eight thousandth of that 120,000TW to keep our technological society running, but it is no easy task to do that.