  This topic review communicates working experiences regarding interaction of a
multiplicity of processes. Our experiences come from climate change modelling,
materials science, cell physiology and public health, and macroeconomic
modelling. We look at the astonishing advances of recent years in broad-band
temporal frequency sampling, multiscale modelling and fast large-scale
numerical simulation of complex systems, but also the continuing uncertainty of
many science-based results.
  We describe and analyse properties that depend on the time scale of the
measurement; structural instability; tipping points; thresholds; hysteresis;
feedback mechanisms with runaways or stabilizations or delays. We point to
grave disorientation in statistical sampling, the interpretation of
observations and the design of control when neglecting the presence or
emergence of multiple characteristic times.
  We explain what these working experiences can demonstrate for environmental
research.
