The difference in ontologies between the old and new conceptions of environment were accompanied by differences in the understanding of environmental limits. Malthus
himself was explicitly concerned with environmental limits—he even did so in a global sense, considering all of humanity and our total environment—but Malthus’ thought on our environment extended only to how much space or capacity there was for people to make settlements, produce food, or exploit resources (Flew, 1970). This is distinct from the environment as an ecological system in which we are enmeshed; an agent in its own right, with its own inputs, outputs, and variables. Environmental Malthusianism is built on an understanding of the environment as much more than just a space to fill with the fruits of human labour; humanity and the environment became viewed as partners in a relationship, and as such, environmental limits took on a wholly different character.
The old environmental limits were a Malthusian ‘check’, a set of iron laws that curbed the population of every species. Even in possessing the ability to manipulate our environment, we could not breach the ultimate barriers of tillable soil and drinkable water. Both classical and neo- Malthusians set these environmental limits alongside the limits of the human animal. For them, we could not escape the innate human traits that convert scarcity into conflict, nor the processes by which proximity enables the spread of disease. These limits were not an ecological problem, they were a problem of space; we were trapped within the confines of a nature whose limits were predetermined.
The new environmental limits are ecological. Population growth and the concomitant growth in the activities of the populace, puts ‘pressure’ on the environment causing it to change. These changes could conceivably render the environment uninhabitable to humans, not simply by over-extending food production or habitable space, but by transforming the natural systems which sustain such production, and possibly even forcing environmental conditions to fall outwith the narrow ranges of temperature, climate, and atmosphere that make human life possible. In the new conception, population pressure can transform the environment before the old Malthusian checks of food shortage and conflict have a chance to work. Limits are not barriers that we bump up against; limits are a multiplicity of lines we can cross—but with consequences.
As ever, these two conceptions do not exist in mutual exclusion from one another. The new environmental limits include the confines of space and the limits of production, but the ultimate consequences of overpopulation are expressed in an entirely new form as a result of the new environmental ontology. In the old conception, environmental limits were a glass ceiling that would stop us if we reached it. Those earlier Malthusians warned that if we did not take responsibility for population growth beforehand, then nature would
dispassionately and forcefully beat us back down to size. In the new conception, the environment is an intricate clockwork mechanism, with population pressure as its spring. The warning of environmental Malthusianism is that if we overwind the spring, the clock will lose time; if we overwind again, the cogs will eventually slip, and the clock will cease to keep time at all.
The practical upshot of environmental limits for both neo- and environmental Malthusians is captured in the concept of ‘carrying capacity’. As is to be expected, the actual meaning of carrying capacity is affected by the ontological difference between the old and new conceptions of environment—which is to say it was once a purely spatial concern, but later took on an ecological character. Appearing in the early 19th century, the phrase ‘carrying capacity’ was initially applied to shipping, referring to the amount of cargo a particular ship could carry after fuel, crew, and ballast were taken into account. The metaphor was later extended to goods carried by cart, by beast, or by hand, and eventually to any ‘thing’ that carries any other thing—as a bee carries pollen, a river carries water, or the wind carries moisture. Its use to describe the capacity of a parcel of land to carry a particular species occurs at the end of the 19th century, as a way for livestock farmers to assess the productivity of their land. This was by no means the ‘invention’ of such assessments; merely the application of a new term to an existing form of knowledge (see Sayre, 2008, for a more exhaustive account of the term and its historical uses).
What makes carrying capacity in this context different from its nominative forebears, however, is the specific epistemic moment in which the term is applied. While authors such as Knibbs (1928) and his contemporaries used the term extensively in the neo-Malthusian sense, elsewhere the science of ecology was beginning to take shape, and the reciprocal relationships between organisms and their environments were coming into focus (Worster, 1994). Land was no longer a space occupied by a fixed number of animals, but a system in which numbers were relative to the geology, ecology, and stewardship of their environment. Carrying capacity was not simply a function of acreage and food; elements such as soil, water, plants, and other species conspired to affect it, producing and consuming resources, providing or stripping out nutrients, casting light and shade, draining or pooling water. If you change elements in the ecology of the land, the carrying capacity changes with it. Alongside the emergence of environmental Malthusianism, carrying capacity came to refer not only to the number of people that could be supported by the available resources, but also to the resilience of the ecosystem
under the pressure of population growth. Environmental limits came to consist of both the spatial limits of productive capacity—shared with the old environmental ontology— and the ecological limits of the Earth’s systems.