Without food we starve, without energy we are poor.

The first part of the title is obvious enough. The average length of time that hunger strikers can live, given adequate fluids, is about 50 days.

The second part requires more development.

Domestication of wildlife - oxen, horses, donkeys etc. - allowed mankind to carry more goods, including himself, and to till more land than his unaided muscles would permit. This increased his wealth by using energy supplied by these domestic animals. The result was to reduce the number of people required to produce food and permit them to create additional goods and services.

Then came the wheel which vastly increased the efficiency of the energy provided by both humans and animals. By doing more with less of its own energy, mankind became richer again.

The example above shows that we can get richer by using more energy but we can also get richer by using energy more efficiently. Think of getting the same level of illumination from a 15 watt compact fluorescent bulb as from a 60 watt incandescent one.

Human and animal power, in the USA but not in some countries, contributes a vanishingly small amount of the energy that supports our current standard of living. Most of that energy is derived from coal, natural gas, and oil.

Since all of these fuels are derived from fossils and, therefore, are not renewable except over geological time scales, they will run out.

Sooner rather than later. Not necessarily in our lifetimes, but sometime.

There is, also, strong - though perhaps not yet definitive - evidence that carbon dioxide, the by-product of burning fossil fuels, is causing potentially disastrous changes to our climate. It is not unreasonable, therefore, to assume that our current energy consumption practices will exhaust our fossil fuel resources and run the risk of irrevocably altering our climate for the worse.

If that is the truth, and it probably is, what obligation do we owe to future generations?

I suggest that we have a very strong moral obligation to future generations - some of whom, if this happens as quickly as has been suggested, are our children and grandchildren.

This means that we must be much more efficient in our use of energy and much more careful in how we generate it. Nuclear power can be an interim, but only interim, solution but, in the end, we will have to rely on the sun, for direct solar energy as well as wind and wave power, and gravity for tidal power.

Those who deny that human activity is causing climate change are demanding that we run a gigantic, uncontrolled, science experiment with the future of humankind, and many other species, at risk if the answer is as many fear.

Buying insurance now, by increasing efficiency and investing in renewable power resources, will be much less costly than responding to the likely disaster.