The first problem with energy is that we are running short of traditional sources of supply.
The International Energy Agency says the world will need almost 60% more energy in 2030 than in 2002, and fossil fuels will still meet most of its needs.
We depend on oil for 90% of our transport, and for food, pharmaceuticals, chemicals and the entire bedrock of modern life.
But oil industry experts estimate that current reserves will only last for about 40 years.
Views vary about how much more will be found or made economically viable to use.
Pessimists predict production will start declining within 15 years, while optimists say we won't have to worry for a century - though rising prices are likely to push us towards alternative energy sources anyway.
Gas, often a suitable replacement for oil, won't last indefinitely either.
There's plenty of coal, but it's still usually hard to use without causing high pollution.
Not everyone depends on the fossil trio, though. Nearly a third of today's world population (6.1bn people) have no electricity or other modern energy supplies, and another third have only limited access.
About 2.5 billion people have only wood or other biomass for energy - often bad for the environment, almost always bad for their health.
That's the second problem - understandably, they want the better life that cheap and accessible energy offers.
But if everyone in developing countries used the same amount of energy as the average consumer in high income countries does, the developing world's energy use would increase more than eightfold between 2000 and 2050.
The signs are already there. In the first half of 2003 China's car sales rose by 82% compared with the same period in 2002.
Its demand for oil is expected to double in 20 years.
In India sales of fuel-guzzling sports utility vehicles account for 10% of all vehicle purchases, and could soon overtake car sales. And the developed world is not standing still.
In the last decade, US oil use has increased by almost 2.7 million barrels a day - more oil than India and Pakistan use daily altogether.
Where our energy comes from is a third problem - energy sources are often long distances from the point of consumption.
Centralised energy generation and distribution systems are fairly new.
A couple of centuries ago virtually everyone would have depended on the fuel they could find within a short distance of home.
Now, the energy for our fuel, heat and light travel vast distances to reach us, sometimes crossing not only continents but political and cultural watersheds on the way.
These distances create a whole host of challenges from oil-related political instability to the environmental risks of long-distance pipelines.
But even if we could somehow indefinitely conjure up enough energy for everyone who wants it, without risking conflict and mayhem in bringing it back home, there would still be an enormous problem - how to use the energy without causing unacceptably high levels of damage to the natural world.
The most obvious threat is the prospect that burning fossil fuels is intensifying natural climate change and heating the Earth to dangerous levels.
But forget the greenhouse effect if you want. There are still real costs that go with the quest for and use of energy: air and water pollution, impaired health, acid rain, deforestation, the destruction of traditional ways of life.
It's one of the most vicious circles the planetary crisis entails.
Cheap, available energy is essential for ending poverty: ending poverty is key to easing the pressures on the planet from the abjectly poor who have no choice but to eat the seed corn. But the tank is running dry.
It doesn't have to be like this. Our energy use is unsustainable, but we already know what a benign alternative would look like.
All we have to do is decide that we will get there, and how.
It will make vastly more use of renewable energy, from inexhaustible natural sources like the Sun and the seas.
One key fuel may well be hydrogen, which is a clean alternative for vehicles and is in abundant supply as it is a chemical component of water.
But large amounts of energy are needed to produce hydrogen from water, so it will not come into its own as a clean alternative until renewable energy is widely available for the process.
Some analysts suggest that nuclear power will be needed to bridge the gap between now and the renewable future.
Many environmentalists (but not all) are deeply unhappy with the idea - fission technology has been in use for a generation, but concerns remain about radioactive waste disposal and the risk of accidents.
Nuclear fusion - a new form of nuclear power which combines atoms rather than splitting them apart - could be ready by around 2040, but that is too long to wait.
However, we can also get energy to do several jobs at once, as combined heat and power plants do. And we can use less of it by becoming energy-efficient.
The British government estimates that 56% of energy used in UK homes could be cut using currently available technologies - yet the original Model T Ford did more miles to the gallon than the average Ford vehicle produced today in the US.
We can install power stations on our roofs by covering our houses with solar tiles, or buying miniature wind turbines the size of a satellite dish.
Practically, the energy crisis is soluble. But reaching the broad sunlit uplands will mean a drastic mental gear change for policy-makers and consumers alike.
AT-A-GLANCE: Global Energy Crisis
(see original article for graphs and figures)
Global energy demand is projected to increase by 60% in the next 25-30 years as developing countries industrialise and rich countries continue to guzzle power, according to the International Energy Agency. Fossil fuels will continue to dominate, estimated to account for 85% of new demand
Carbon emissions - thought to be a major cause of global climate change - are set to increase by 60%. As developing countries' share of world energy demand surges from 38% to a predicted 48%, poor countries are expected to contribute two-thirds of the projected increase in carbon emissions.
Transport will play an increasing role in rising demand for oil as vehicle ownership surges in the developing world. The International Energy Agency says oil stocks will last up to 2030 and beyond, but suggests prices will become more volatile as the more accessible reserves are depleted.
Renewable energy use is predicted to increase by nearly 60%, but this will do little more than keep pace with rising overall demand. By 2030, renewable sources (not including biomass and nuclear) will have increased only 1% from 3% to 4% of total world use. However, costs for most types of renewable energy are expected to decrease.
AT-A-GLANCE: Where the World's Oil Lies
(see original article for graphs and figures)
Where the Oil Is
The Middle East remains the biggest player in oil.
The region dwarfs the rest of the world, when it comes to reserves, ensuring its prominence on the global political stage. Saudi Arabia alone possesses 25% of the world's proved reserves.
The North Sea and Canada still have substantial reserves, but they would prove very expensive to extract.
How Long Will It Last?
The short answer is no-one knows, but even the oil industry suspects the world "peak" is now approaching.
It says it has 40 years of proven reserves at the moment - but it also said that 30 years ago.
In fact, the estimate has actually increased in recent years as production has fallen. Cutting consumption would prolong oil's life.
The Middle East is also the biggest oil producer, currently providing nearly one-third of the world's total.
But Europe and Eurasia (mainly Russia and the UK) and North America are also big producers.
The difference is, nearly all the Middle East oil is for export while Europe and the US do not produce enough to meet their own needs.
Imports and Use
Western Europe and Japan are heavily dependent on oil imports as production cannot meet massive domestic demand.
The gas-guzzling US is the world's largest per-capita oil consumer but produces much of its requirements itself.
Producers in the Middle East, where oil costs so little, are also heavy users. Poorer countries consume much less per head.
The Cost of Oil
For a century the price of oil remained stable. But it soared when the oil cartel Opec blocked exports to the West after the 1973 Arab-Israeli war.
Prices tripled, plunging the West into recession. The Iranian revolution had a similar impact, and prices peaked again after the two Gulf wars.
The Cost of Driving
The rising price of oil has had a predictable effect on the price of petrol.
In the US the price of regular gasoline has risen by more than a third since the beginning of 2002.
In the UK the rise has been less steep because more - much more - of the pump price is made up of tax.
AT A GLANCE: Alternatives to Oil
(see original article for graphs and figures)
The prospect that oil might one day run out, together with the growing threat from global warming, means the need for alternative energy sources has never been greater.
A key lesson from decades of burning exhaustible fossil fuels is the importance of renewable - or at least less damaging - sources.
Click on the links to view some of the options.
It is abundant and clean – water vapour is the only waste product - but needs to be processed for use as fuel.
It will need to switch to sustainable sources and be harnessed, stored and distributed economically before it can become the alternative fuel of choice.
Some cars already use it and it is currently being tested on some London buses.
The exposed UK is ideally placed to take advantage of the world’s fastest-growing renewable-energy choice.
Modern windmills are environmentally friendly and use an endless – if fluctuating – source.
But their noise and obtrusiveness have generated some complaints, and the cost of setting up windfarms remains an obstacle.
Hydro-power is safe and pollution-free, but is limited by location and the upheaval it can cause.
Hydro-electric power, where vast amounts of water are stored and then released at force, needs big sites; wave and tidal power need coastlines and can be costly to set up.
The UK’s first wave-energy station, connected to the National Grid, is in Islay.
It’s been around a long time, but it’s taken a while to develop an effective way of harnessing the Sun’s energy.
Now, though, solar panels are a feature of many homes, generating electricity via photovoltaic cells.
They are now also being tested on sound barriers on the M27 in Hampshire to provide electricity as well as noise protection.