Why was stratospheric ozone disappearing above the South Pole? Do Now.
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Transcript of Why was stratospheric ozone disappearing above the South Pole? Do Now.
Why was stratospheric ozone disappearing above the
South Pole?
Do Now
ArtScience Prize Information
SCIENCE AND THE SKY
Solving the mystery of disappearing ozone
CHAPTER 2 SCIENCE LITERACY AND THE PROCESS OF SCIENCE
OZONE
A molecule of 3 oxygen atoms (O3)
A natural component of the stratosphere that shields the Earth
from UV rays
WHAT IS?
Ozone found in the troposphere
is harmful to living things.
Ozone is a key element of the atmosphere, the blanket of gases surrounding our planet.
THE ATMOSPHERE
Composed of several layers that differ in density, gas composition, and temperature
Answering scientific questions requires
the Scientific Method
a body of facts and explanations
SCIENCE IS
the process used to gain that knowledge
AND
It’s worth noting that facts may change as more data is collected.
limited to asking questions about the natural world: physical phenomena that can be objectively observed
SCIENCE IS
What are my dogs thinking?
SCIENCE IS NOT subjective, ethical, or spiritual questions
OBSERVATION INFERENCE
Information gathered with our senses or equipment that extends our senses
Explanation of what might have caused the observed phenomenon
The key culprit: chlorofluorocarbons (CFCs)Human-made molecules:•Coolants for refrigeration and air conditioners (Freon)• Dispersants in aerosol
cans• Styrofoam production
What depletes ozone?
Lower than normal ozone levels in the atmosphere
CFCs might be causing the
ozone to disappear
Inference?
Observation?
Do CFCs cause ozone depletion?
HYPOTHESISA tentative explanation for an observation
PREDICTIONGenerally an “if…, then…” statement based on the hypothesis
Good hypotheses are testable and falsifiable.
Science proceeds by acceptance or rejection of hypotheses.
Hypotheses can never be “proven correct.”
Ozone formation and breakdown
Wrap Up
• What pieces of evidence could scientists collect to show the impact of Earth’s 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 CFC’s and the Ozone Layer.
HYPOTHESISA tentative explanation for an observation
PREDICTIONGenerally an “if…, then…” statement based on the hypothesis
HYPOTHESIS CFCs 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.
• 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
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)
Could something other than CFCs be causing ozone
depletion?
Ozone concentration (DU), Antarcticaannual October averages
CFC12 concentration (ppt) global average
Types of variables
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
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?
Ozone/UV radiation experiments
The Scientific Method
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?
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)
So how do we solve the problem?
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 Actione.g., Montréal protocol – 1987Susan Solomon’s 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
2011 20752050
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
“It’s clear that ozone will ultimately recover but it’s 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?