An activity input is an exchange entering an activity from another activity or from the environment. These inputs represent the flows of materials, energy, services, and resources required for an activity to function and produce its outputs. Activity inputs can be either intermediate exchanges from other human activities within the product system or elementary exchanges drawn directly from the natural, social, or economic environment.
Land transformation, land occupation, and working hours are all considered exchanges from the environment, representing services provided by the environment to the activity. These inputs capture the use of environmental resources and human labour that support production processes, even though they may not involve physical material flows in the traditional sense.
Inputs of primary production factors of the economy, including labour costs, net taxes, net operation surplus, and rent, are also classified as exchanges from the environment. This classification applies even when these factors are measured as economic costs rather than physical flows. By treating these economic inputs as environmental exchanges, life cycle assessment can account for the full scope of resources and services required to support economic activities, ensuring a comprehensive evaluation of all dependencies and contributions throughout a product system.
