Thus HCC is probabilistic at any one time and changes in time with changing human knowledge and choices and natural constraints. Ecological limits appear, not as ceilings, but as unavoidable trade-offs among competing values regarding population, economics, the environment and culture. In collaboration with economists, technologists, geologists and others, ecologists can illuminate HCC by increasing and applying ecological knowledge to clarify both the trade-offs available to humans and the consequences of possible choices. For example, water use for irrigation imposes trade-offs between population size and dietary options. Sustainable management of the biosphere.
Human influence is now discernable in even the most remote reaches of the biosphere.
Physical limits to human activities are increasingly evident in the deteriorating condition and growing scarcity of essential resources, such as land, water, and the capacity of the environment to transfer and transform chemical wastes. For example, over 40 percent of Earth's terrestrial vegetated surface has diminished capacity to supply benefits to humanity because of recent direct impacts of land use, representing a ca. 10 percent reduction globally in its potential direct instrumental value. With regard to water, humanity now uses ca. 26 percent of total terrestrial evapotranspiration and ca.