What’s Happening to our Tropopause ?
15th May 2006
Donald Burfitt-Dons

First of all what is the tropopause? Well, it’s the dividing line between the troposphere, which is the lowest layer in the atmosphere and significantly the part where all the weather activity takes place, and the stable layer above called the stratosphere. Although the height of the tropopause is lower at the poles in general it lies at an altitude of between 40 and 50,000 ft. And how do we know when we have reached it? Pilots check their outside air temperature gauges and when they read -56.5 degrees Celsius they know they are there for all practical purposes.

The temperature of the troposphere decreases at a quite regular rate of 1.98 degrees Celsius per thousand feet up to the tropopause. From there on up into the stratosphere it gradually increases again until it is about the same as at sea level i.e.15 degrees Celsius.

Because the temperature does not change significantly as aircraft climb above the tropopause over the years aviation has accumulated a long and detailed data base on the height of the tropopause. Back in the days of the early commercial jets, OAT(outside air temperature) readings were logged every hour. Today this is done electronically.

A study of this data has revealed the rather amazing fact that the world wide level of the tropopause has risen by 900 feet over the last twenty years. A change of that magnitude over such a short time span must be viewed with great concern. Although, in numerical terms it only amounts to about 2%, when one considers the maths of a circle and a sphere it takes on a new dimension. The 2% becomes just under 6% in terms of volume. That is to say that over a twenty year period the encompassing atmospheric blanket on which we depend for life has pushed out significantly into the stratosphere.

Nobody knows exactly why that is as yet but it is another wake up call and further fingerprint evidence of Man’s impact on the environment.