The Deadly Combination of Heat and Humidity – NYTimes.com

The Deadly Combination of Heat and Humidity – NYTimes.com.

A sobering and thought provoking article.

Humans have a very narrow comfort zone in terms of their physiological limits of temperature, pressure, humidity, oxygen and CO2 levels etc. So the trend mentioned in the article should be a dire warning to us.

Underlying all this is the classic problem of large deviations – that explains how often extreme events can occur, that can wipe out a species.  In engineering, this is related to the theory of measuring the mean time to failure of a product.

One simple but generally poorly understood fact is the following. If the mean value of a Normal (Gaussian) random variable is undergoing a secular linear drift with time, then the probability that it will make a large deviation above a certain fixed level increases exponentially! This is easy to work out using the properties of the tail of the distribution as described by the Q-function and upper and lower bounds on it. And, as many of you may know, any random variable that is an additive composition of several independent or weakly independent random variables (as is the case in most natural phenomena)  is asymptotically normal – this is called the weak law of large numbers. So the large deviation property is applicable widely in nature. (In fact the property that large deviation probability scales exponentially fast as the mean drifts linearly is applicable to a much wider class of distributions, over and above normal distributions.)

In any case, what this mean in simple term is the following:

On a given day we routinely see temperature swinging by several degrees, in fact in summer in places like Ontario Canada I have experienced first hand temperature swings as large as 25 degrees Centigrade. So when climate scientists say that the average temperature of the oceans or of the atmosphere is drifting up at 0.1 degrees per decade, why should we  worry about that at all ÉÉ

The answer is that even if the average temperature is drifting up only by 0.1  deg C per decade, the probability of hitting some high value where humans cease to function, like 120 deg C, grows exponentially each decade. So if in 1950s the probability was one day per decade, in 1960s the probability would be 1 day per year, and in 1970s, one day per month etc. (I am making the numbers up just for the sake of illustrations. You can easily do your own research to find out the precise numbers.) Think of the cost of this in terms of precious human lives. If 10 people were dying due to heat waves in a country in 1950s, in the next decade 100 were dying, and in the decade after that 1000 were dying, and so on. All this simply follows from the large deviation property I described earlier. Thus a seemingly minute secular linear drift in average temperature is causing untold human carnage.

Then there is also the cost to our economy. Since our economy is highly predicated on insurance, and since insurance companies are highly leveraged across domains and markets, the occurrence of extreme events  at exponentially higher probabilities means that our premiums go up exponentially too, or even worse, certain kinds of coverage such as flood or wind damage will not be offered any more! This will put a huge damper on housing and industrial activity and  could cause the world economy to come to a screeching halt.

Thus, people who call themselves economic conservatives, and crib about the economic impact of environmental regulations, should think carefully about the long term disastrous impact of not regulating the industries that cause climate change and the resulting burden they place on the economy. 

Dealing with climate change requires long term thinking as opposed to short term opportunism, and I ardently hope that our politicians will find the courage and the wisdom to do the right thing.

More importantly I hope we, as voters, will find the courage and wisdom to vote the right people into power!