Environmental Mythology

ENVS 202 On-line Access

The Space Shuttle: Destroyer of Ozone

A wonderful example of myth perpetuation occurred in Winter term 97 in an anonymous sociology class on the UO campus. At that time a student who was enrolled in 202 was also in this sociology class in which the professor insisted that the Space Shuttle was a major source of chlorine deposition in the stratosphere and that the Government is covering this up.

Now this is a professor saying this so naturally, students today will now accept it as the "truth" because, after all, that's what they heard the professor say.

When will this kind of nonsense stop? And I don't mean the nonsense of some professors, but the general student attitude of assigning ultimate credibility to authority figures. Always ask them for data or evidence of back up what they are espousing.

Good data is the most effective manner to suppress mythology. So why is it then so hard to suppress this particular myth?


Space shuttles put a lot of chlorine into the stratosphere

True of False:

In support of truth:

The role of chlorine radicals in ozone depletion, it was hypothesized that HCL from solid rocket motors might have a significant effect upon the ozone layer - if not globally, perhaps in the immediate vicinity of the launch.

A hypothesis is not the same as the Truth. A hypothesis only becomes the "Truth" after its rigorously tested

Testing the hypothesis through measurement:

Each shuttle launch produces about 200 metric tons of chlorine as HCL, of which about one-third, or 68 tons, is injected into the stratosphere. This is because the shuttle spends only a couple of minutes in transit through the stratosphere.

The residence time of HCL deposited in this manner is about three years. A full year's US schedule of shuttle and solid rocket launches injects 725 tons of chlorine into the stratosphere. The European Space Agency's Ariane rocket makes a similar contribution, with 57 tons of HCL deposited in the stratosphere for each launch.

So yes, rocket launches do insert Ozone depleting chlorine radicals into the stratosphere so the myth must be, in fact true.

Are we done? Have we proven our hypothesis?

Key Question Is 725 tons of CL a lot?

Hell no, these inputs are completely negligible compared to chlorine emissions in the form of CFC's and related compounds (~ 1.0 million tons/yr in the 1980's, of which ~0.3 Mt reach sources of stratospheric chlorine, which amount to about 75,000 tons per year. [Prather et al.] [WMO 1991] [Ko et al.]

75,000 is a lot bigger than 725. End of myth.

Another popular myth, often spouted by the well-known authority shown below:

is that Volcanoes destroy Ozone

Why is this scary:

So what's the point of all of this?

If you want to make a positive impact in Environmental Policy and Public Participation forums you need to be able to

Data Reliability

Data reliability involves the determination of the extent to which the data sample can address the question. For data samples widely distributed over time, one can raise the issue of the reliability of data taken with older instruments.

Data reliability is an issue when you can not measure a phenomena directly but instead you have to use some tracer.

For example:

What is the best way to measure the extent of urban air pollution?

What is the best way to measure acid rain?

Another good example of the issue of data reliability is evidence for Global Warming:

Issues to raise:

Let's see the data:

Here is some Global Data whose reliability is high. There is no doubt that CO_2 in the atmosphere is increasing.

Methane concentration from ice core data!

This shows strong exponential growth in the last 100 years or so - consistent with growth in the world's population.

Finally, what about the wide spread belief that things are always getting worse:





Lead Emission

204,000 tons

5,000 tons

Factor 40 reduction

Aluminum Cans Recycled

1.2 billion

47 billion

Factor 40 increase

Passive Solar Houses


2 million

Factor of 75 increase

Tons of Garbage

121 million

160 million

marginal increase

Percentage of Oil Imported




World CO2 Emissions

14 billion tons/yr

21 billion tons/yr

Climate Change

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