Few of us would care to predict today how we shall be living in 2023.
By Alex Kirby
BBC News Online environment correspondent
But governments do not have that luxury: they have to try to think what may be happening 20 years from now.
Keeping the lights on and the wheels turning in the UK two decades hence depends on decisions taken today.
So warnings about energy security are bound to be taken very seriously.
The Institution of Civil Engineers (ICE) says the UK could face power cuts in 20 years' time, because it will depend so heavily on foreign energy sources to produce its electricity.
The institution says 80% of the gas needed to fuel British power stations will come from distant and "politically unstable" countries by then.
In an ideal world, most countries would by 2023 be well on the way to reliance on clean and renewable energy sources, like wind, wave and solar power.
The potential wind energy available in the US is estimated at more than double the amount of electricity generated there today.
Solar Century, a UK company which provides solar PV (photovoltaic) installations, makes even more ambitious claims.
Coal's day might come again
It says: "Solar PV-generated power could provide 10,000 times more energy than the world currently uses.
"If we covered a small fraction of the Sahara desert with PV, we could generate all the world's electricity requirements."
In February 2003, the UK Government published its energy white paper, spelling out how it planned to cut the pollution blamed for climate change.
By 2020, it said, Britain should be producing 20% of its electricity from renewables.
Not so worried
Crucially, it said no new nuclear power stations should be built at present, though it did not rule them out some time in the future.
The director-general of ICE, Tom Foulkes, says the UK is a long way from the big new gas fields being developed in central Asia and Africa.
He says: "Can the security of the UK's gas supply be guaranteed, given that it will have to travel thousands of miles in a series of pipelines that are vulnerable to mechanical failure, sabotage and terrorist attack?"
But other analysts are not persuaded that future political instability in the countries supplying Britain's energy need be a devastating threat.
John Mitchell is an associate fellow of the UK's Royal Institute of International Affairs (RIIA), known also as Chatham House.
He told BBC News Online: "The key to energy security is diversity of supply. I think it is far-fetched to say we face a threat of power shortages.
"In five years or so we'll have a much clearer idea whether renewables can deliver those very ambitious White Paper targets.
"If they can't, the only other possibilities will be nuclear power or imports of either natural gas or coal.
No common thread
"I think it would be at least 15 years before you could expect to see any new nuclear stations running here, if they were chosen.
"On natural gas imports, we do underestimate the flexibility we have with our various sources of supply.
Renewable energy has huge potential
"We'd be looking at imports from Russia, and from Algeria, Nigeria, Trinidad and perhaps Iran. And they don't share a common set of political problems.
"With coal, you're looking at countries like the US, Australia, Venezuela and Colombia. It's a viable option, though its carbon dioxide emissions add to climate change and that is a problem."
Stewart Boyle, an energy analyst, told BBC News Online: "Any country that's over-dependent on a single fuel and a small number of suppliers could be in trouble.
"The ICE report is timely, and shows we have to concentrate on renewables. That way we're in control of our own destiny.
"And remember, electricity supplies less than a fifth of our energy needs in Britain. Most of the energy we use for heating, and that's critical."