David P. Turner / January 27, 2022

Environmental scientists define natural capital in the context of natural resources management.  It commonly refers to a “stock of materials or information” that yields a flow of ecosystem services: an ocean fishery produces a yield of fish; a forest landscape produces a yield of wood.  In practice, most ecosystem services are produced by a combination of natural capital and human management.

In the case of hunter/gatherers, the human contribution to production of harvested food was limited.  But as technology became more important in provision of ecosystem services, the human element (including machines and knowledge) began to dominate.

A problem has arisen because humans have tended to consume not only ecosystem services (flows) from natural capital, but also the nature-built capital (stocks) itself.  A striking example is the cod fishery in the North Atlantic Ocean:  overfishing led to a collapse of the cod population and an abrupt decline in productivity.   

For centuries, humans have gotten away with depleting or destroying natural capital by simply moving on to the next unexploited natural resource.  Commodity frontiers often have a geographic dimension, e.g. the wave of primary forest exploitation in temperate North America that extended from the New England hardwoods, through the pines of the Great Lakes states, and on to the Pacific Northwest conifers.

A massive erosion of nature-built capital over the last two centuries is evident in the spatial patterns of land use change, distortions in animal and plant population structure, and outright extinction of species.  As natural capital is depleted, human interventions (often subsidized by energy from fossil fuels) must be ramped up to maintain the same level of ecosystem services.

From an Earth system science perspective, we can describe the interaction of the human enterprise and natural capital in terms of interaction of the technosphere with its natural resources base. 

The technosphere is the global aggregate of human made artefacts and includes machines, buildings, transportation infrastructure, and communications infrastructure, along with the humans and their knowledge needed to maintain it.  Estimates of technosphere manufactured capital are on the order of 800 Pg. 

The technosphere requires a large stream of materials and energy to maintain itself and to produce the outputs of goods and services that keep the 7.8 billion people on Earth alive.  Here, I am particularly interested in the interaction of the technosphere with the biosphere.

Biosphere capital is the sum of all organisms and the associated information in the form of genetic material.  It is a subset of global natural capital. 

Biosphere mass is estimated at 550 Pg (carbon) and the estimates for the number of species range from 5.3 million and 1 trillion.  Inputs to the biosphere include solar energy and material flows from the geosphere (minerals) and hydrosphere.  Besides sustaining itself, the biosphere outputs vast flows of food and fiber (including wood) to the technosphere. 

From the global perspective, technosphere manufactured capital is clearly increasing and biosphere capital is clearly decreasing.  Examples include:

1. The aforementioned degradation of marine fisheries by overharvesting.  Correspondingly, the mass of fishing boats is thought to be on the order of 30% higher than needed for a sustainable global catch of high value species.
2. The continued conversion of intact ecosystems to agriculture use (estimated at 50% of the land surface) or urban development (Figure 1).
3. The loss of soil organic matter by erosion and oxidation associated with agriculture. 

Our limited understanding of the biosphere makes it difficult to even quantify the on-going loss of biosphere capital.  Note that the biosphere contributes to regulation of atmospheric and marine chemistry by way of the global biogeochemical cycles.  Thus, as we lose biosphere capital, we are beginning to lose those free regulatory services.

Meanwhile, technosphere manufactured capital is growing at a rate of 1-8% per year, depending on the level of development in a given country.  It will likely peak at a much higher level than at present because of the still growing global population and increases in per capita manufactured capital in the developing world.

In principle, biosphere inputs to the technosphere can be derived in a sustainable manner.  A landscape of tree plantations can be continuously harvested and replanted to produce a sustained yield of wood.  Plantation forests supplied about one third of industrial roundwood in 2000.  Likewise, there is such a thing as a sustainable marine fishery if the harvest is properly managed. 

However, much of the current material transfer from biosphere to technosphere is drawing down biosphere capital.  Differentiating between sustainable and depleting production of food and fiber, and increasing attention to sourcing, will play an important role in the transition to a soci-economic metabolism that is sustainable.  Accounting practices that treat all forms of capital – including natural capital and technosphere capital in its various forms (manufactured, financial, human, social) – is necessary.

The view of ecosystem services as a co-production of technosphere capital and natural capital offers a way forward.  Essentially, all ecosystem services must now be managed as socio-ecological systems, i.e. as a coupling of a human subsystem, having full stakeholder participation, and a regenerating biophysical subsystem.

Since different natural resources must be managed at different scales, a hierarchy of socio-ecological systems is needed.  This arrangement points to the importance of zonation on the Earth surface in terms of the strength of the coupling between technosphere and biosphere.  We can have large areas of relatively undisturbed intact ecosystems (e.g. marine reserves and terrestrial wilderness areas), significant areas of heavy technosphere dominance (as in urban and industrial zones), significant areas of intensive food and fiber production (e.g. forest plantations), and a scattering of areas with a moderate intensity of biosphere/technosphere interaction.  This view supports the development of spatially-explicit simulation models – implemented at a range of spatial scales – that can be used within a socio-ecological system to organize the co-production of ecosystem services. Potentially, with a well-designed combination of monitoring, modeling, and environmental governance, the technosphere will drive increases rather than decreases in biosphere capital (e.g. the recovery of whale populations).