1
How do scientists study the natural world? Why do we say science is a “process” and that conclusions are always open to further study?
INFOGRAPHICS 2.3 AND 2.4
Why is the statement “It is wrong to inflict pain on animals” not scientifically testable?
This statement is not scientifically testable because it is not falsifiable by any demonstration of empirical evidence. This is a valuable question that deserves to be pursued but it is an ethical question whose answer might vary in different cultures.
Let’s say that you are going to test whether exposure to UV-B radiation causes cells to become cancerous. Why is it necessary to have a control group in this experimental study?
You need to feel like you have some kind of control over your experiment.
It is not actually necessary in this type of experiment.
You need to make sure cells not exposed to UV-B radiation don’t turn cancerous.
You need to determine how likely it is that cells not exposed to UV-B radiation will turn cancerous.
D
Some people reject the explanation that the hole in the ozone layer is caused by CFCs on the basis that it is “just a theory.” These people:
are correct if they are using a different line of evidence to support their conclusions.
are equating the term scientific theory with an untested hypothesis or a guess.
do not understand the chemistry involved in ozone depletion.
are requiring that the explanation gain the status of hypothesis before they will accept it as probably true.
B
2
What is stratospheric ozone, and why are scientists worried about its depletion?
INFOGRAPHIC 2.1
Tanning beds use light that is mostly UV-A radiation and only 1%-3% UV-B radiation. Does this mean they are safe to use?
Yes. They deliver less UV-B radiation than you would get if you laid out in the Sun for a tan.
No. Even though exposure to UV-A radiation is safe, tanning beds still deliver some dangerous UV-B radiation.
Yes. Having a tan means you won’t get a sunburn or other skin damage.
No. UV-A radiation is also damaging, so this exposure is not without risk.
D
Ozone, a component of smog, is a dangerous substance that can damage sensitive tissue such as lungs. So why is it okay, and even necessary, to have ozone up in the stratosphere?
In the stratosphere, ozone helps to absorb some UV-B and UV-A, thus limiting the amount that reaches the Earth’s surface and the organisms that live there (like us). If we were up in the stratosphere trying to breathe, then the ozone there could cause us problems but of course we are never up that high — even most jets do not fly that high. On the other hand, we are down on the surface so being exposed to ozone down here, in the form of smog, can cause problems so we need to take steps to avoid that exposure.
3
What lines of evidence suggest that CFCs are causing the depletion of stratospheric ozone?
INFOGRAPHICS 2.2 AND 2.5
What is the relationship between CFCs and ozone in the stratosphere?
Ozone naturally breaks down in the stratosphere, but substances like CFCs regulate its re-formation so that less-harmful UV radiation reaches Earth’s surface.
Ozone from the stratosphere migrates down to the troposphere, where it reacts with chemicals like CFCs to produce more oxygen.
Ozone in the stratosphere is broken down by chemicals like CFCs, but as CFCs themselves are broken apart by UV radiation, ozone depletion slows.
Ozone is naturally formed and broken down in the stratosphere, but substances like CFCs catalyze additional ozone breakdown, which results in increased UV radiation reaching Earth’s surface.
D
What is a correlation in science? How is it different from a cause-and-effect relationship? Explain how both types of relationships are used to understand the connection between CFCs and stratospheric ozone.
A correlation is observed when two things occur together, but we don’t know which is cause and which is effect, or whether the two trends occur together by coincidence (something else entirely may be causing both to occur or they may be totally unrelated). Atmospheric sampling revealed that in areas of the stratosphere where CFCs were highest, ozone levels were lower than normal (a negative correlation). To answer the question of whether CFCs could cause ozone breakdown, a laboratory experiment that exposed ozone to CFCs in the presence of UV-B could be done to test the hypothesis that UV-B induced CFC breakdown would release a Cl atom which could then break apart ozone. We would predict to see the ozone-chlorine product, ClO, if this reaction does indeed take place. If we obtain this product we have established a cause-and-effect relationship that links CFCs to ozone breakdown.
4
Why are both observational and experimental studies needed to investigate the natural world? How does statistics help researchers analyze the data they gather from these studies?
INFOGRAPHIC 2.6
Scientists want to know whether ocean water is becoming more acidic due to the extra CO2 that is released by the burning of fossil fuels. They have set up monitoring sites in the water to collect daily data on the water’s pH. This is an ____________ study.
observational
Other scientists decide to add extra CO2 to tanks of ocean water that contain coral to see if the lower pH harms the animals by weakening their skeletons. This is an __________ study.
experimental
Identify at least three circumstances in which it would be more acceptable or reasonable to conduct an observational study than to conduct an experimental one.
When gathering initial evidence for a new area of investigation, when studying complex systems that cannot be manipulated or easily controlled (such as the atmosphere), or when investigating questions for which the manipulation of subjects would not be ethical.
5
How do approaches that use the precautionary principle and adaptive management help policy makers address environmental problems?
INFOGRAPHIC 2.7
True or False: Adaptive management focuses on finding a solution that seems best and sticking with it.
FALSE
When is it reasonable to invoke the precautionary principle when setting policy?
When there is uncertainty about what will happen but the potential for a very bad outcome if nothing is done is high. This is the “better safe than sorry” approach.
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