and states that “Global temperatures in February remained below the long term average, thanks to the La Nina – but despite decades of allegedly catastrophic man-made warming.”
As can easily be seen from the graph, the zero line is not the long-term average, at least in the ways in which this term is usually used (the average for the instrumental record going back 150 years, or else the estimated pre-industrial average). It’s the average for the UAH satellite data set, which only started in 1979, when warming was well under way. Since there has been a steady long-term warming trend over the thirty years of data, the average of the data set corresponds to the average temperatures prevailing in the mid-1990s, as you can easily see by eyeballing the data, or, if you prefer, confirm by statistical analysis. (The National Academy of Sciences did this a few years ago IIRC).
So, what Bolt doubtless meant to write is that the effect of this La Nina, one of the strongest in the historical record, was sufficient to offset about 15 years of the warming trend – I guess one-and-a-half decades counts as “decades” in some sense.
Actually, there’s a nice symmetry here. On Spencer’s preferred measure of a 13-month moving average, 2010 (a transition from El Nino to La Nina) was almost exactly as warm as 1998 (the most powerful El Nino year in the record).
So, Bolt’s point goes both ways. Fifteen years of trend warming at the current rate is about 0.2 degrees C, which roughly matches the difference between the peak or trough of the ENSO cycle and the midpoint.
Unfortunately, with emissions and concentrations still rising, and sinks being saturated, the warming trend is likely to accelerate in coming decades. To quote Bolt again, the effects could well be catastrophic.