  Nonlinear initial value turbulence simulations often exhibit large temporal
variations in their dynamics. Quantifying the temporal uncertainty of
turbulence simulation outputs is an important component of validating the
simulation results against the experimental measurements, as well as for
code-code comparisons. This paper assesses different methods of uncertainty
quantification of temporally varying simulated quantities previously used
within plasma turbulence community, to evaluate their strengths and potential
pitfalls. The use of Autoregressive Moving-Average (ARMA) models for
forecasting the uncertainty of turbulence quantities at later simulation times
is also studied. These discussions are framed in the practical context of
calculating the time-averaging uncertainties of turbulent energy fluxes
calculated via gyrokinetic simulations. Particular attention is paid to how
standard approaches are challenged as the driving gradient is reduced to the
critical value for instability onset.
