The argument for "monetizing"—or putting a monetary value on—ecosystem functions may be stated thus: Concern about the depletion of natural resources is widespread, but this concern, in the absence of an economic argument for conservation, has not translated into significant conservational progress. Some critics blame this impasse on environmentalists, whom they believe fail to address the economic issues of environmental degradation. Conservation can appear unprofitable when compared with the economic returns derived from converting natural assets (pristine coastlines, for example) into explicitly commercial ones (such as resort hotels). But according to David Pearce, that illusion stems from the fact that "services" provided by ecological systems are not traded on the commodities market, and thus have no readily quantifiable value. To remedy this, says Pearce, one has to show that all ecosystems have economic value-indeed, that all ecological services are economic services.Tourists visiting wildlife preserves, for example, create jobs and generate income for national economies undisturbed forests and wetlands regulate water runoff and act as water—purifying systems, saving millions of dollars worth of damage to property and to marine ecosystems. In Gretchen Daily’s view,monetization, while unpopular with many environmentalists, reflects the dominant role that economic considerations play in human behavior, and the expression of economic value in a common currency helps inform environmental decision-making processes.