During this century consumption has increased exponentially until more than half of commercial energy comes from these two sources. Even optimists calculate that oil and gas will be acutely scarce in a few decades if current trends continue. Although coal has been used over a longer period, there appear to be sufficient reserves for a century or more. Given the dominant role of fossil fuels in energy supply, dramatic changes will be needed to conserve them even if the pollution impacts are ignored. It is also significant that oil is potentially more valuable in the long term as a source of raw materials for the chemical industry than it is as a fuel.
Renewable energy is one of three kinds of continuous resource.
Solar radiation is both a continuous resource in itself and also the motive power of natural cycles which supply air and fresh water as well as wind, hydro and wave energy. Natural ecosystems offer a harvest of animal and vegetable products or can be cleared to use the soil to grow agricultural crops. So the resource base exists for a move to renewable energy and the economics are competitive. What seems to be lacking at present in most countries is the political will, perhaps because renewable energy technologies are still seen as 'low-tech' or 'alternative', and therefore suspect. Also, a move to the use of continuous resources may require a move to a more dispersed supply, and so raise problems of organization and ownership in sustaining the resource and distributing the benefit.