19 Wrap UpWhat pieces of evidence could scientists collect to show the impact of Earth’s depleted ozone layer? (Observation to inference)
20 Do NowFrom 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 HYPOTHESISCFCs are breaking down O3.PREDICTIONIF 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 worldNo manipulation of subjectsCan only show correlationsObservational studiesData collected by manipulating variablesUses test group(s) and control group(s)Can show cause and effectExperimental studies
24 CORRELATION CAUSE and EFFECT When two things occur together, but one does not necessarily cause the otherWhen 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), Antarcticaannual October averagesCFC12 concentration (ppt) global average
26 Types of variables Control variable(s) Dependent variable(s) Independent variable(s)The factor being manipulatedThe response of an organism or the characteristic that is measuredAll other things should be held constant during the experiment.
27 provides the standard of comparison for the test group(s) Types of groupsTest group(s)group(s) that is exposed to different levels of the independent variableControl group(s)provides the standard of comparison for the test group(s)the “baseline”Replicationrepetition of treatments(including controls)conducting the experiment many times
28 How do I know if my groups are really different? STATISTICSDetermine if differences exist between test and control groupsAssign a level of certainty to our conclusionsA probability value (or P value) is used todetermine 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?
35 Montréal Protocol –1987 Administered by the U.N. A plan developed to phase out CFCsBy 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 actionThe U.S. banned CFCs in certain productsin 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 Actione.g., Montréal protocol – 1987Susan Solomon’s studies published – 1988
38 Adaptive managementA 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-1980ozone levelsPolar regions back topre-1980ozone 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 UpThe 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?