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Why was stratospheric ozone disappearing above the South Pole?

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Presentation on theme: "Why was stratospheric ozone disappearing above the South Pole?"— Presentation transcript:

1 Why was stratospheric ozone disappearing above the South Pole?
Do Now Why was stratospheric ozone disappearing above the South Pole?

2 ArtScience Prize Information

AND THE SKY Solving the mystery of disappearing ozone


5 A molecule of 3 oxygen atoms (O3)
WHAT IS ? OZONE A molecule of 3 oxygen atoms (O3) A natural component of the stratosphere that shields the Earth from UV rays

6 Ozone found in the troposphere is harmful to living things.

7 THE ATMOSPHERE Ozone is a key element of the atmosphere, the blanket of gases surrounding our planet. Composed of several layers that differ in density, gas composition, and temperature


9 Answering scientific questions requires
the Scientific Method

10 SCIENCE IS a body of facts and explanations AND
the process used to gain that knowledge It’s worth noting that facts may change as more data is collected.

11 SCIENCE IS limited to asking questions about the natural world: physical phenomena that can be objectively observed

12 SCIENCE IS NOT subjective, ethical, or spiritual questions What are my dogs thinking?

13 OBSERVATION INFERENCE Information gathered with our senses
or equipment that extends our senses Explanation of what might have caused the observed phenomenon

14 What depletes ozone? The key culprit: chlorofluorocarbons (CFCs)
Human-made molecules: Coolants for refrigeration and air conditioners (Freon) Dispersants in aerosol cans Styrofoam production

15 Do CFCs cause ozone depletion?
Lower than normal ozone levels in the atmosphere Observation? Inference? CFCs might be causing the ozone to disappear

16 HYPOTHESIS PREDICTION A tentative explanation for an observation
Generally an “if…, then…” statement based on the hypothesis

17 Good hypotheses are testable and falsifiable.
Science proceeds by acceptance or rejection of hypotheses. Hypotheses can never be “proven correct.”

18 Ozone formation and breakdown

19 Wrap Up What pieces of evidence could scientists collect to show the impact of Earth’s depleted ozone layer? (Observation to inference)

20 Do Now From the discussion we had in class yesterday… Formulate a hypothesis and prediction about the relationship between CFC’s and the Ozone Layer.

21 HYPOTHESIS PREDICTION A tentative explanation for an observation
Generally an “if…, then…” statement based on the hypothesis

22 HYPOTHESIS CFCs are breaking down O3. PREDICTION IF polar clouds and sunlight were causing Cl to react with O3, THEN many ClO molecules should be found in the atmosphere.

23 How do you test hypotheses?
Data collected in the real world No manipulation of subjects Can only show correlations Observational studies Data collected by manipulating variables Uses test group(s) and control group(s) Can show cause and effect Experimental studies

24 CORRELATION CAUSE and EFFECT When two things occur together,
but one does not necessarily cause the other When two things occur together, but one directly occurs (the effect) in response to, or as a result of, the other (the cause)

25 Could something other than CFCs be causing ozone depletion?
Ozone concentration (DU), Antarctica annual October averages CFC12 concentration (ppt) global average

26 Types of variables Control variable(s) Dependent variable(s)
Independent variable(s) The factor being manipulated The response of an organism or the characteristic that is measured All other things should be held constant during the experiment.

27 provides the standard of comparison for the test group(s)
Types of groups Test group(s) group(s) that is exposed to different levels of the independent variable Control group(s) provides the standard of comparison for the test group(s) the “baseline” Replication repetition of treatments (including controls) conducting the experiment many times

28 How do I know if my groups are really different?
STATISTICS Determine if differences exist between test and control groups Assign a level of certainty to our conclusions A probability value (or P value) is used to determine significance between groups: typically 5% or less (i.e., P<0.05), i.e., we are 95% sure our conclusions are correct

29 Is ozone depletion (and increased exposure to UV rays) causing higher rates of skin cancer?

30 Ozone/UV radiation experiments

31 The Scientific Method

32 Do Now What are the steps that a scientist would undergo to conduct research, and have their findings understood as a “theory” by the scientific community?

33 THEORY A widely accepted explanation for a natural phenomenon that has been extensively and rigorously scientifically tested A theory can never be “proven” (e.g., the CFC hypothesis)

34 So how do we solve the problem?

35 Montréal Protocol –1987 Administered by the U.N.
A plan developed to phase out CFCs By 2009, every country had signed the agreement; governments developed their own policies for reduction of CFCs.

36 Translating values into action
Policies = Translating values into action The U.S. banned CFCs in certain products in the 1970s. In the early 1990s, the U.S. started phasing out CFCs entirely. Industry, public, and government sectors cooperated to find solutions to this problem.

37 The precautionary principle
Though you are not 100% sure of what is causing a problem, there is a big risk to “doing nothing.” Taking Action e.g., Montréal protocol – 1987 Susan Solomon’s studies published – 1988

38 Adaptive management A plan that allows you to alter strategies as new information comes in or the situation changes (e.g., the original Montréal protocol target list is not comprehensive)

39 The Montréal protocol and amendments
Predicted abundance of chlorine in the stratosphere (thousand ppt)

40 Present and future ozone levels 2011 2050 2075
Largest ozone “hole” ever recorded above the Arctic! Mid-latitude areas back to pre-1980 ozone levels Polar regions back to pre-1980 ozone levels

41 “It’s clear that ozone will ultimately recover but it’s also clear that it will take many decades to do so.” – Susan Solomon

42 Wrap Up The depletion of the ozone layer is a great example of how science documented a problem and its cause, and public action confronted the problem. Can you think of other examples of this? What current issues need this attention?

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