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?