Human life has evolved to depend on the functions performed by intact ecosystems. These ecosystem services include water and air filtration, flood control, pollination, moderation of disease spread, and natural beauty. All are vulnerable to degradation by human activity.
Ecosystem services, while interdependent, can be thought of in four categories: supporting (soil, habitat); regulatory (filtration, climate moderation); provisioning (food, water); and cultural (hiking, hunting). The biodiversity from which these services flow constitutes the natural capital on which human life depends. The World Bank estimates the annual worth of ecosystem services worldwide at $44 trillion—nearly twice the gross world product. But the UN’s 2005 Millennium Ecosystem Assessment found that, of 24 ecosystem services examined, 60% were being steadily degraded; one of the lead authors estimated that $3–$5 trillion of natural capital is lost every year.
In the U.S., the President’s Council of Advisors on Science and Technology (PCAST) has noted that population growth, rising affluence, and reliance on destructive technologies combine to put intense pressure on ecosystem services. These pressures take various forms—clear-cutting, overfishing, polluting, introducing invasive species, and more—but all risk reaching thresholds at which ecosystems collapse. One reason for this pressure is that ecosystem services are perceived as free goods, and people or corporations benefit from exploiting natural capital but, says PCAST, "are able to avoid most of the attendant damages, which are spread across society.”
A number of programs have been developed to help companies and governments incorporate ecosystem services into decision-making. The U.S. Environmental Protection Agency is conducting ongoing research and developing a Web-based “National Atlas for Sustainability,” and the Natural Capital Project offers its InVEST software to help governments, corporations, and nonprofits model the effects of potential decisions on environmental, economic, and social concerns.
Accounting for ecosystem services can be difficult, but one way to do so is to consider the “replacement cost”: the cost of using technology to replicate the service provided by the ecosystem. For example, New York City avoided building a $6 billion water treatment plant by paying farmers upstream $1 billion to reduce animal waste and fertilizer in runoff. The World Bank estimates that only one-third of a forest’s economic value is its timber production; cutting that timber can negatively affect the forest’s other services and can impact human needs such as hydroelectric power or agricultural productivity.
The built environment contributes to the loss of ecosystem services, and some ecology-minded designers aim to quantify the predevelopment services associated with a site, and then meet or exceed that level of service, or “ecological performance standard,” post-development.