Wrap Up What pieces of evidence could scientists collect to show the impact of Earths depleted ozone layer? (Observation to inference)
Do Now From the discussion we had in class yesterday… Formulate a hypothesis and prediction about the relationship between CFCs and the Ozone Layer.
HYPOTHESIS A tentative explanation for an observation PREDICTION Generally an if…, then… statement based on the hypothesis
HYPOTHESIS CFCs are breaking down O 3. PREDICTION IF polar clouds and sunlight were causing Cl to react with O 3, THEN many ClO molecules should be found in the atmosphere.
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 How do you test hypotheses? Experimental studies
CORRELATIONCAUSE 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)
Could something other than CFCs be causing ozone depletion? Ozone concentration (DU), Antarctica annual October averages CFC 12 concentration (ppt) global average
Types of variables Control variable(s) Dependent variable(s) Independent variable(s) All other things should be held constant during the experiment. The response of an organism or the characteristic that is measured The factor being manipulated
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 Types of groups Replication repetition of treatments (including controls) conducting the experiment many times
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 How do I know if my groups are really different?
Is ozone depletion (and increased exposure to UV rays) causing higher rates of skin cancer?
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.
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.
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 Solomons studies published – 1988
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)
The Montréal protocol and amendments Predicted abundance of chlorine in the stratosphere (thousand ppt)
Present and future ozone levels 201120752050 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
Its clear that ozone will ultimately recover but its also clear that it will take many decades to do so. – Susan Solomon
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?