Reversible Record Breaking and Variability: Temperature Distributions across the Globe

Based on counts of record highs and lows, and employing reversibility in time, an approach to examining natural variability is proposed. The focus is on intrinsic variability; that is, variance separated from the trend in the mean. A variability index alpha is suggested and studied for an ensemble of monthly temperature time series around the globe. Deviation of <alpha > (mean alpha) from zero, for an ensemble of time series, signifies a variance trend in a distribution-independent manner. For 15 635 monthly temperature time series from different geographical locations (Global Historical Climatology Network), each time series about a century-long, <alpha > = -1.0, indicating decreasing variability. This value is an order of magnitude greater than the 3 sigma value of stationary simulations. Using the conventional best-fit Gaussian temperature distribution, the trend is associated with a change of about -0.2 degrees C (106 yr) (1) in the standard deviation of interannual monthly mean temperature distributions (about 10%).