We illustrate variability of seasonal temperature in units of standard deviation (σ), including comparison with the normal distribution (“bell curve”) that the lay public may appreciate. The probability distribution (frequency of occurrence) of local summer-mean temperature anomalies was close to the normal distribution in the 1950s, 1960s and 1970s in both hemispheres (Fig. 2). However, in each subsequent decade the distribution shifted toward more positive anomalies, with the positive tail (hot outliers) of the distribution shifting the most.
Last year it was the USA and Australia, today it is India that is suffering from a heatwave, with temperatures approaching 50C. Above 50C/120F, in dry air, proteins begin to break down (and plants die). Furthermore, a Wet Bulb temperature of 35C (which causes animals to die because they overheat) is reached at 40% relative humidity. So much for global warming being beneficial. If, like me until recently, you struggle with all this meteorological stuff, here is a nice graph from Wikipedia that tells you all you need to know about Wet and Dry Bulb temperatures and Relative Humidity. I know this chart is complicated but, the important bit is the pale blue line with a “35” next to it. The top right corner of the graph (beyond this line) is therefore what you could call the “death zone” and the higher the Dry Bulb temperature (vertical lines in green) the lower the Relative Humidity (curves in red) required to enter it.