Roger B said:

 Is there any engineering behind this?

It's a political decision (and not in a bad way).  Nothing to do with engineering.  You decide that something needs to be done, then ask an engineer how to do it.

Roger B said:

Are there sufficient resources available?

I'm sure there are if we want there to be.

Roger B said:

How much more fossil fuel will be consumed producing these alternative energy sources before they become in some way self-sustaining'?

Quite a bit.  But extracting, refining and transporting fossil fuels uses a lot of fossil fuels.  As does building fossil-fuel powered power stations.

But the more renewables you build, the less fossil fuels you need going forwards.

Roger B said:

1) They are entirely shareholder driven, it is their fiduciary duty to maximise profits by staying with oil and gas and they don’t see a risk of ending up with ‘frozen assets’.

2) They don’t want to see the world run out of energy when renewables can’t deliver.

I'm sure it's entirely option 1.  We're talking about oil companies here.

Simon,

You have highlighted some of the key points here:

‘By 2050, no energy must come from fossil fuels’

It's a political decision (and not in a bad way).  Nothing to do with engineering.  You decide that something needs to be done, then ask an engineer how to do it.

Is it just a political decision then, not based on any science? Do the people setting these ‘political’ targets actually know what they are talking about?

Are there sufficient resources available?

I'm sure there are if we want there to be.

All these resources, metals, plastics, concrete, space, etc. are finite. It is not just a matter of wishing there to be enough. The given target, ‘By 2050, no energy must come from fossil fuels’, needs calculations to determine what will be required to replace all the heat energy used in metal and concrete manufacture with electrical energy. This includes the very high losses if hydrogen is used .  

How much more fossil fuel will be consumed producing these alternative energy sources before they become in some way self-sustaining'?

Quite a bit.  But extracting, refining and transporting fossil fuels uses a lot of fossil fuels.  As does building fossil-fuel powered power stations.

But the more renewables you build, the less fossil fuels you need going forwards.

This also requires some significant calculations. If you believe the climate science your ‘Quite a bit’ will further increase global temperatures and probably push past a tipping point. Does that mean we are doomed anyway? Probably not, but some good simulations will give a rate of conversion to alternative energy sources that will minimize the consumption  of fossil fuels. This requires science and engineering, not a ‘political’ target of 2050.

Is it just a political decision then, not based on any science?

Te two aren't mutually exclusive - most governments are advised by various learned committees who presumably do know their stuff.

  - Andy.

One may look at the line mega city as an example of an oddly conceived vanity project,   or at least as the sort of thing that I hope would never gain traction in Europe, yet that will have plenty of respected experts working on the designs and planning. If it really is using 20% of the worlds steel for the foreseeable future, as that link suggests, then its a good job that there aren't 5 places on the planet trying to do the same  scale of thing at once.

Not all state driven projects necessarily stand up to the 'is it sensible? ' test.

Mike

PS and if sense came into it, albeit at a far more modest scale, in the UK we'd have built the northern legs of HS2 first, then cancelled the southern bit not the other way about....

One may look at the line mega city as an example of an oddly conceived vanity project,   or at least as the sort of thing that I hope would never gain traction in Europe, yet that will have plenty of respected experts working on the designs and planning. If it really is using 20% of the worlds steel for the foreseeable future, as that link suggests, then its a good job that there aren't 5 places on the planet trying to do the same  scale of thing at once.

Not all state driven projects necessarily stand up to the 'is it sensible? ' test.

Mike

PS and if sense came into it, albeit at a far more modest scale, in the UK we'd have built the northern legs of HS2 first, then cancelled the southern bit not the other way about....