As previously said, the classic authors’ ideas, especially the Malthus’s ones, have had certain continuity until nowadays, so they are currently still valid. However, we have to point out that the debate on the resources has moved on to studying the population impacts on the environment and how they affect the real availability of the natural resources, rather than to reflecting on their probable shortage of resources.
Then, the updated Malthusian idea is that the population growth is the cause of most current global environmental problems: the resources shortage, the malnutrition, the pollution increase, the deforestation and the desertification.
This idea has been graphically shown by Paul Ehrlich in his book The Population Bomb (1968). Ehrlich introduces the I=PAT formula, where the Environmental Impact (I) is the result of the volume combination of the population (P), the level of richness or the per capita consumption (A) which is measured by the per capita product or the consumption level, and the technological level or production efficiency (T). Therefore, the formula presents the population (P), the affluence (A) and the technology (T) as the main origin of the environmental impact (I).
The major criticism provided for this perspective states that Ehrlich has reduced the environmental impact, which is such a complex phenomenon, to a quantitative generalisation, without taking into account the local-level features of the resources use; and that, at the same time, the factors interrelated in the formula are not independent to each other, but on the contrary, they are mutually connected in a quite complex way. Another criticism for Ehrlich’s theory was provided by Julian Simon, an economist that declares (by following Boserup’s ideas) the population growth as a beneficial process. So, he refutes the Neo-Malthusian theory by arguing that the resources price is currently falling, and therefore, the population growth causes a technological development (investigation on new energy sources, higher agricultural output, for instance) and consequently reduces the environmental impact.