The BBC's Alex Kirby looks at the challenge of providing the world with energy without damaging the environment, as part of Planet Under Pressure, a BBC series on environmental issues.
The first problem with energy is that we are running short of traditional sources of supply.
We depend on oil for 90% of our transport
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.
There is plenty of coal, but it can cause major pollution
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.
Air pollution is a major problem - often related to energy use
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.