Page 491 - Environment: The Science Behind the Stories

FAQ Is the ozone hole related to global 30 Montreal
warming?
This is a common misconception held by the public. Some 25 Protocol
people are under the impression that the depletion of strato- 20
spheric ozone helps to prevent global warming by letting heat Millions of sq km 15
or greenhouse gases out of the atmosphere. Other people
suppose that ozone depletion worsens warming by letting 10
heat into the atmosphere. Neither is true. Ozone depletion
lets in excess ultraviolet radiation from the sun, but this does 5
not appreciably warm or cool the atmosphere. Research 0
published in 2011 suggested that the ozone hole may in fact 1979 1985 1990 1995 2000 2005 2010
affect atmospheric circulation and rainfall in the Southern Year
Hemisphere, and perhaps researchers will discover other
connections between aspects of climate change and ozone Figure 17.27 The Antarctic ozone hole grew quickly after its
appearance, but phase-outs of ozone-depleting substances
depletion. However, on the whole the two phenomena are
very different and largely unrelated. beginning in 1987 have halted its growth. Data from NASA, reflect-
ing averages from 7 Sept. to 13 Oct. each year.

We addressed ozone depletion The ozone layer is not expected to recover completely
with the Montreal Protocol until 2060–2075. Much of the 5 billion kg (11 billion lb) of
CFCs emitted into the troposphere has yet to diffuse up into
In response to the scientific concerns, international policy the stratosphere, so concentrations may not peak there until
efforts to restrict production of CFCs bore fruit in 1987 2020. Because of this time lag and the long residence times
with the Montreal Protocol. In this treaty, signatory nations of many halocarbons, we can expect many years to go by
(eventually numbering 196) agreed to cut CFC production before our policies have the desired environmental effect.
in half by 1998. Five follow-up agreements deepened the Indeed, it is common for there to be a time lag between our
cuts, advanced timetables for compliance, and addressed response to an environmental problem and the resolution
additional ozone-depleting substances (Figure 17.26). The of the problem. This is one reason scientists often argue
substances covered by these agreements have now been for proactive policy guided by the precautionary principle
mostly phased out, and industry has been able to shift to (p. 283), rather than reactive policy that risks responding
safer alternative chemicals that are inexpensive and efficient. too late.
As a result, we have evidently stopped the Antarctic ozone One challenge in restoring the ozone layer is that nations
hole from growing worse (Figure 17.27)—a success that all can plead for some ozone-depleting substances to be exempt
humanity can celebrate. from the ban. For instance, the United States was allowed to
continue using methyl bromide, a fumigant used to control
15 pests on strawberries. Yet despite the remaining challenges,
the Montreal Protocol and its follow-up amendments are
widely considered our biggest success story so far in address-
Montreal
Effective stratospheric chlorine (parts per billion) 10 5 London 1. Informative scientific research developed rapidly, facili-
ing a global environmental problem. The success has been
1987
No protocol
attributed to several factors:
1990
tated by new and evolving technologies.
2. Policymakers engaged industry in helping to solve the
problem. Industry became willing to develop replace-
Beijing 1999
running out and firms wanted to position themselves to
profit from next-generation chemicals.
Zero emissions Copenhagen 1992 ment chemicals in part because patents on CFCs were
0 3. Implementation of the Montreal Protocol after 1987
1980 2000 2020 2040 2060 2080 2100 followed an adaptive management approach (p. 333),
Year adjusting strategies midstream in response to new scien-
Figure 17.26 The Montreal Protocol reduced stratospheric tific data, technological advances, or economic figures.
ozone depletion, and follow-up agreements in London,
Copenhagen, and Beijing reduced it still more. In this graph, Because of its success in addressing ozone depletion, the
the y-axis values give a collective measure of ozone-destructive Montreal Protocol is widely viewed as a model for interna-
potential from all substances. Data from Emmanuelle Bournay, UNEP/ tional cooperation in addressing other pressing global prob-
GRID-Arendal, http://maps.grida.no/go/graphic/effects-of-the-montreal-protocol- lems, from biodiversity loss (p. 315) to persistent organic
490 amendment-and-their-phase-out-schedules. pollutants (p. 402) to climate change (pp. 528–529).

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