Most people think of early warning in terms of immediate and short-term concerns such as major weather events (hurricanes, cyclones, tornadoes), climatic variations (El Niño events, or droughts caused by lack of rainfall), or geo-physical events like earthquakes and tidal waves. These immediate and often unpredictable events require specific measuring and advisory systems. Specifically targeted national and international organizations focus on the early warning of these events. UNEP/DEWA supports these activities and is directly involved in partnerships designed to ensure the more timely delivery of data and information on such natural hazards. However, UNEP/DEWA primarily focuses on identifying issues which take much longer to develop and might better be identified as "emerging environmental threats." These may take four forms:
- Environmental degradation that increases the vulnerability of ecosystems (often in combination with socio-economic stresses);
- Cumulative environmental threats where the accumulation of pollutants collectively increases the vulnerability of ecosystems;
- Environmental threats that have not been perceived as such in the past, but new evidence has indicated that they must now be considered as potentially deleterious to ecosystems; and
- More speculative, long-term issues where scientific evidence may be inadequate at present but discussions and assessments have identified a possible environmental problem.
This type of early warning is as important as providing forecasts of tornadoes, for example; the differences being the immediacy of occurrence and the potential ability of ecosystems to adapt or mitigate these emerging threats. Depending on the relative socio-economic vulnerability of a given community, these environmental threats can (drastically) alter ecosystem functioning and have a major impact on human security and the biodiversity of the planet. The recognition that environment is a key ingredient of development has made the ability to provide early warning on longer-term and cumulative environmental threats more important and it is therefore a key activity of UNEP/DEWA.