The ecological revolution solved problems of incalculable seriousness by converting social and economic decline into sustainable growth, leading in the long run to improved living standards for most people; in historical terms, these have reached incredible heights in the course of the twentieth century. However, this has not been achieved without creating new problems. For one thing, it must be assumed that the subterranean forests upon which energy supplies now mainly depend will be used up in the same way as ordinary forests were. At the moment, subterranean energy is being used very rapidly: As much energy is now being consumed annually, worldwide, as was deposited in the course of a million years during the carboniferous period. Furthermore, the increasing discharge of carbon dioxide (CO2) that is a consequence of using fossil fuel endangers the climate. In the middle of the eighteenth century the concentration of CO2 in the atmosphere was about 260 ppm. Since then, as a result of burning coal and oil, close on 500 billion tonnes of CO2 have been released, which means that the carbon dioxide concentration today is 345 ppm, and by the year 2000 will have risen to 370 ppm; in the event of an unaltered rate of increase the concentration will have reached 600 ppm by the year 2050.

One of the first to warn of the potential danger to the stability of the world climate represented by anthropogenic carbon dioxide was the Danish physiologist August Krogh (1874–1949.) Nevertheless, much time was to pass before the problem became visible.