From SDC(UK): The Earth as a whole is approximately a steady state. Neither the surface nor the mass of the earth is growing or shrinking; the inflow of radiant energy to the Earth is equal to the outflow; and material imports from space are roughly equal to exports (both negligible). None of this
means that the earth is static—a great deal of qualitative change can happen inside a steady state, and certainly has happened on Earth. The most important change in recent times has been the enormous growth of one subsystem of the Earth, namely the economy, relative to the total
system, the ecosphere.
This huge shift from an “empty” to a “full” world is truly “something new under the sun” as historian J. R. McNeil calls it in his book of that title. The closer the economy approaches the scale of the whole Earth the more it will have to conform to the physical behavior
mode of the Earth. That behavior mode is a steady state—a system that permits qualitative development but not aggregate quantitative growth.
Growth is more of the same stuff; development is the same amount of better stuff (or at least different stuff). The remaining natural world no longer is able to provide the sources and sinks for the metabolic throughput necessary to sustain the existing oversized economy—much less a growing one. Economists have focused too much on the economy’s circulatory system and have neglected to study its digestive tract.
Throughput growth means pushing more of the same food through an ever larger digestive tract; development means eating better food and digesting it more thoroughly. Clearly the economy must conform to the rules of a steady state—seek qualitative development, but stop aggregate quantitative growth. GDP increase conflates these two very different things.
We have lived for 200 years in a growth economy. That makes it hard to imagine what a steady-state economy (SSE) would be like, even though for most of our history mankind has lived in an economy in which annual growth was negligible. Some think a SSE would mean freezing in the dark under communist tyranny. Some say that huge improvements in technology (energy efficiency, recycling) are so easy that it will make the adjustment fun.