Even if we assume that production of ozone depleting substances will stop, and
that all countries will be in full compliance, the claims that the ozone layer
will recover are based on scientific understanding of our atmosphere that,
while improved from ten years ago, is still far from perfect. Science has
consistently under, rather than over-estimated the speed and severity of ozone
depletion. Clearly this history points to the need for policy to err on the
side of caution.
Reassuringly though, there is no single area of global ecological
science that is as clearly established as the connection between industrial chemicals and
ozone depletion. In 1994, NASA scientists announced the results of a major
study that conclusively proved the connection between ozone loss and CFCS -
once again confirming Rowland's and Molina's hypothesis.
What is still debated among credible scientists is at what levels depletion
will bottom out and when we will reach them. According to United Nations
Environment Programme projections, (upon which negotiators depend
in the Montreal Protocol) the ozone layer will fully recover by the middle of the next
century, and ozone depletion is expected to reach its peak around the year
1998. As mentioned before, those projections are based on full compliance.
UNEP projections are also based on the best available science, and on the
assumption that there will be no positive feedbacks, or nasty surprises, that
could accelerate ozone depletion. Several trends are disturbing in this regard.
For the past three years, ozone depletion has outstripped the predicted rate
of ozone loss. At first, in 1993, scientists noted that "the decline over much
of the United States, Europe, and Asia may only be a transitory effect from the
eruption of the Mt. Pinatubo volcano...If that is the case ozone levels should
return to more normal levels in a year or two..."[New York Times, 4/23/93] The
next year, UNEP reported that as the aerosols from Pinatubo had been swept out
of the air, ozone levels had returned to levels consistent with the models.
However this year, the US National Oceanic and Atmospheric Administration
(NOAA) and the World Meteorological Organization both reported "unusually low
ozone levels", up to 35 percent depletion in some areas. In addition, this
year a new and unexplained depletion happened over the southern hemisphere in
the summer, which runs completely counter to model predictions.
Ozone depletion is only one of the global ecological crises facing Earth's
atmosphere today. The other is climate change, caused by global warming.
Scientific opinion is now clear that human activity is linked to the global
warming of the atmosphere. (New York Times, 9/10/95) We know that greenhouse
gases trap heat, and we know that the concentrations of these gases are rising
in our atmosphere. The debate now is over how severe and where the impacts
will be - an experiment on a global scale. Disturbingly, several models have
predicted that as climate change accelerates, it could also exacerbate ozone
depletion. Ironically, HFCs, a major replacement chemical for CFCS, are also
potent global warming gases.
Clearly something else is going on in the stratosphere. The Pinatubo aerosols
are gone. However, we still are not able to fully and accurately predict the
behavior of the ozone layer. Until we can (and that point may be decades away)
we must err on the side of caution in designing policies to protect the
atmosphere.
