Early in the 19th century, economists were concerned with limits to growth due to limits to per capita output. By the mid-20th century, capital was seen as the engine of growth. It was thought than an increase in capital per worker would lead to a decline in the marginal product of capital, and to a decline in savings until finally investment in capital would only be sufficient to replace depreciated capital. Then it was argued that this limit would not be reached because of technological innovation.
The idea that growth may be limited by natural resources and the environment was known throughout the first half of the 20th century but only seriously addressed by mainstream economists after the publication of Limits to Growth in 1972. This report lost currency in the 1980s with the decline in prices of raw materials and agricultural products, and with continued major discoveries of oil and mineral deposits.
Limits today are defined more in terms of limits to the assimilative capacity of ecosystems. It is estimated that only a reduction of 70-90% of current material and energy throughput could allow for an economy which is both ecologically sustainable and internationally just.
It has been suggested that any argument regarding limits should concern itself with a limited time frame of 100 years, since predictions beyond this time are highly uncertain given the unknown potential of technological development.
Three major issues are: (1) the substitutability of anthropogenic capital for natural capital; (2) the limits to agricultural output; and (3) the capacity of the environment (atmosphere, oceans etc.) to act as a sink for wastes, and the ability to reduce waste in the face of economic expansion.