The environmental issues that may become priorities in the 21st century can be clustered in the following groups: a) unforeseen events; b) scientific discoveries; c) sudden, unexpected transformations of old issues; and d) well-known issues to which the present response is inadequate - although their long-term environmental consequences are well known.
Environmental scanning is a tool by which planners and others can obtain information both about the specific topic area in which they are located and their general environment. The environmental scanning system can identify important emerging issues that may constitute either obstacles or opportunities. This process helps institutions allocate their resources in a way that anticipates or responds to changes in the external environment. Originally used for economic trend purposes, it was broadened to include technological trends, and social and environmental factors in the 1970's.
Environmental scanning can also be divided into two groups. They are passive and active scanning. Passive scanning is ongoing scanning at an almost unconscious level. No specifications are made with regard to resources or criteria for scanning and decisions made on this type of scanning activity are usually [ad hoc]. Active scanning on the other hand, involves a much higher level of attention with information sources being scanned specifically for their expected contents. The criteria is also different with active scanning in that specific questions are asked by the scanner such as whether this item or issue has relevance to the organization or community and whether its likely effect, justifies following it more closely.
Human environmental impacts now include unprecedented changes at global level in the atmosphere and the stratosphere. Climatologists project that greenhouse gas accumulation in the lower atmosphere will change the world's climate and has apparently already begun to do so. Depletion of stratospheric ozone has occurred in recent decades. The relationship between the two phenomena is complex and new knowledge is emerging. Authoritative international reviews have concluded that these global environmental changes will affect human health, mostly in adverse ways. At global level, some of the ongoing changes in patterns of human disease are compatible with the advent of climate change. However, further research is needed to clarify these and future relationships.