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Physical Geography Part 3 Script
Hello!
Today we’re going to be taking a look at how human interaction has affected the atmosphere causing
ozone depletion due to chlorofluorocarbons (we call CFC’s for short) which have caused ozone
depletion, most noticeably at the poles. This has led to an international outcry for change which
culminated in the universal acceptance of the Montreal Protocol stopping the use of CFC gases by all
countries represented in the United Nations. Before we cover those topics, I would like to recap on what
we have learned in the last lecture. In the last lecture we covered the composition of the atmosphere. In
general, whenever we refer to a general layer, we call it by the sphere name for example: the
troposphere, stratosphere, mesosphere, thermosphere, and exosphere. When we are concerned with
the top of the layer or the area between layers, we refer to the pause name for example: Tropopause,
stratopause, mesopause, and thermopause. It has been a general rule until recently that temperature
decreases with increasing altitude. This is only true in the troposphere, however, when we get into the
stratosphere, the temperature increases with increasing altitude, then in the mesosphere, the
temperature decreases with increasing altitude, and finally, when our altitude ascends higher into the
thermosphere the temperature increases beyond 120⁰ Fahrenheit. The atmosphere is primarily
composed of the following gases which remain constant: Nitrogen78%, oxygen21%, and Argon1%. It’s
also important not to forget about the effect of water vapor in the troposphere which by the way water
vapor cannot ascend higher than the troposphere due to the fact that the temperature drops below
freezing so you will not even find a wisp of cloud beyond the troposphere. Water vapor can make up
about 4% of the volume of the atmosphere over areas like the tropics. However, in deserts and polar
areas, water vapor makes up a fraction of 1%.
Human-Induced Atmosphere Change
As world population grows and the use of industrial technology intensifies, human activity has
increasingly had unintended and uncontrolled effects on the atmosphere—effects seen around the
globe. This human impact, in simplest terms, consists of the introduction of impurities into the
atmosphere at a pace previously unknown—impurities capable of altering global climate or harming
forms of life. Although for many years a concern of atmospheric scientists, over the last decade
especially, the consequences of human produced changes in the atmosphere—especially global climate
change—have received international attention from not only the scientific community but from the
general public as well. In June 2009, the United States Global Change Research Program, a joint scientific
effort involving more than a dozen federal agencies and the White House, issued its latest report,
entitled Global Climate Change Impacts in the United States. Building on the findings of the Fourth
Assessment Report of the Intergovernmental Panel on Climate Change, the report offers a candid
assessment of climate change in the United States:
“Climate change is apparent now across our nation. Trends observed in recent decades include rising
temperature, increasing heavy downpours, rising sea level, longer growing seasons, reductions in snow
and ice, and changes in the amounts and timing of river flows. These trends are projected to continue,
with larger changes resulting from higher amounts of heat-trapping gas emissions, and smaller changes
from lower amounts of these emissions. The observed changes in climate are already causing a wide
range of impacts, and these impacts are expected to grow.”1
Depletion of the Ozone Layer:
About 90% of the Ozone layer is primarily situated in the stratosphere where it functions as a shield and
absorbs ultraviolet radiation protecting life here on Earth. Prolonged exposure to UV radiation is linked
to skin cancer—both the generally curable nonmelanoma varieties as well as much more serious
melanoma; it is also linked to increased risk for cataracts; it can suppress the human immune system,
diminish the yields of many crops, disrupt the aquatic food chain by killing microorganisms such as
phytoplankton on the ocean surface, and may have other negative effects still undiscovered.
Scientists have discovered that the Ozone Layer has a hole and the size of that hole has been increasing.
The reason for the hole in the Ozone Layer is caused by Chlorofluorocarbons (CFCs). These CFCs are
widely used in refrigeration and air-conditioning (the cooling liquid Freon is a CFC), in foam, and plastic
manufacturing, and in aerosol sprays. Although extremely stable and inert in the lower atmosphere,
CFCs are broken down by ultraviolet radiation once they reach the ozonesphere. Under the influence of
UV radiation, a chlorine atom is released from a CFC molecule; the chlorine atom then reacts with
ozone, breaking it apart to form one chlorine monoxide (CIO) molecule and one O₂ molecule. The
chlorine monoxide molecule can then react with a free atom of oxygen, forming a diatomic oxygen
molecule while freeing the chlorine atom to react with another ozone molecule. As many as 100,000
ozone molecules can be destroyed for every chlorine atom released. 2
Scientist have used a computer system called TOMS (Total Ozone Mapping Spectormeter) to monitor
ozone levels throughout the world since 1979. A hole has been discovered in the Antarctic and a whole
1
Hess, Darrel, and Tom L. McKnight. "Chapter 3: Introduction to the Atmosphere." McKnight's physical geography:
a landscape appreciation. 10. ed., international ed. Boston: Prentice Hall, 2011. 54. Print.
2
Hess, Darrel, and Tom L. McKnight. "Chapter 3: Introduction to the Atmosphere." McKnight's physical geography:
a landscape appreciation. 10. ed., international ed. Boston: Prentice Hall, 2011. 55. Print.
has been discovered in the Arctic in 1980; so why is it the case that it’s the poles that have larger areas
of ozone depletion in comparison to other areas of the world? This is due to the extreme cooling that
goes on in the poles and in particular the Antarctic during the winter. There are polar vortexes which are
whirling wind patterns that occur here which isolates polar air in the atmosphere which forms ice
crystals in the stratosphere which form thin clouds called polar stratospheric clouds (PSC). These clouds
can accelerate the process of ozone destruction. The surface of the ice crystals provide an area where a
number of reactions can occur including the accumulation of chlorine based molecules. Stratosphereic
ozone depletion has been correlated with increased levels of ultraviolet radiation reaching ground level
in Antarctica, Australia, mountainous regions of Europe, central Canada, and New Zealand.3
The Montreal Protocol
These discoveries were sufficiently alarming that a number of countries including the United States
banned the use of CFCs in aerosol Sprays in 1978. A major international treaty—the Montreal Protocol
on Substances That Deplete the Ozone Layer—was negotiated in 1987 to set time tables for phasing
out the production of the major ozone-depleting substances. More than 189 countries, including all
major producers of ozone-depleting substances, have ratified the proposal. Following stipulations of the
treaty and its more recent amendments, the industrialized countries of the world had banned CFC
production by 1996. Moreover, the protocol signatories pledged a fund of more than $700 million to
help developing countries implement alternatives to CFCs and end their production by 2010. Even with
the Montreal Protocol fully implemented, the ozone layer will not recover immediately because the
reservoir of CFCs in the atmosphere may persist for 50 or 100 years. The largest measurable Antarctic
ozone hole was observed in 2006, and since then it appears that ozone loss is stabilizing. However, some
studies suggest that it may be 2050 before recovery is well under way. Addressing the depletion of the
ozone layer is considered by many scientists to be an example of an environmental success story: a
human-produced problem was identified, and a global strategy was implemented to counteract it. In
2009, an international team of scientists led by NASA’s Paul Newman used computer models to predict
what would have happened if CFC use had not been curtailed by the Montreal Protocol. Their study
suggested that without the ban on CFC use, by the year 2100 ozone levels over the tropics would have
collapsed to levels found today in the Arctic and Antarctic—resulting in summertime UV radiation levels
more than three times greater than what is considered “very high” today.4
Today we have covered the effect that humans have on the atmosphere and the positive and negative
consequences that result from those effects. The chlorofluorocarbons which had been used in aerosols
and in Freon which is used in refrigerators have harmed the ozone layer; in particular the ozone layer
over the poles had received the most damage. This led to an international action culminating in the
Montreal Protocols which banned the use of chlorofluorocarbons (CFCs) in the world. It’s interesting to
3
Hess, Darrel, and Tom L. McKnight. "Chapter 3: Introduction to the Atmosphere." McKnight's physical geography:
a landscape appreciation. 10. ed., international ed. Boston: Prentice Hall, 2011. 55. Print.
4
Hess, Darrel, and Tom L. McKnight. "Chapter 3: Introduction to the Atmosphere." McKnight's physical geography:
a landscape appreciation. 10. ed., international ed. Boston: Prentice Hall, 2011. 57. Print.
note that this is the only treaty which had received unanimous agreement in the world. As a result, the
ozone layer is beginning to stabilize. In the next lecture we are going to dive into the controls of
weather and climate.