HillMurray High School Atmospheric Science Worksheet

Welcome to our 40th day of class:22 April 2022
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Possible role of humans in enhancing the
observed global warming
Assignments:
◆ Lecture quiz for today, due 11:59 PM on
Sunday, 24 April
◆ Weather Notebook entry for today
04/25/2022
AHS 104 Day 40 Spring 2022
1
Conclusion from last time:
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Globally, the surface air temperature has
increased over the past century by ~1°C.
All lines of evidence are consistent.
◆ Instrumental record of rising surface air
temperature
◆ Global retreat of Alpine glaciers
◆ Reduction in ice sheets and Arctic sea ice (not
Antarctic sea ice)
◆ Rising sea level
04/25/2022
AHS 104 Day 40 Spring 2022
2
The big question: is this increase
natural, human-caused, or a
combination?
04/25/2022
AHS 104 Day 40 Spring 2022
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Global Warming
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Given the evidence of trends in surface air
temperature, sea level rise, and global retreat of
alpine glaciers, scientific hypotheses can be
developed to explain the trends.
Let’s consider the most commonly held
hypothesis.
04/25/2022
AHS 104 Day 40 Spring 2022
4
First some review: Greenhouse Effect
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Greenhouse gases (primarily water vapor but also
CO2 and others) absorb IR from surface and radiate
it back to Earth’s surface
Net result = warming of the surface by 60°F!!
There’s no controversy about this naturally
occurring effect!!
But is the greenhouse effect being enhanced by
human activities?
Do added greenhouse gases = a warmer planet?
04/25/2022
AHS 104 Day 40 Spring 2022
5
How would GHGs (e.g. CO2) heat the atmosphere?
(all of the IR-related components get bigger with more
GHG in atmosphere)
Numbers are
percentages of
incoming solar
radiation
30% is reflected
to space
Net=111-64-96=-49
-64
CO2 cools the
atmosphere!!
+111
-96
But CO2 heats the
Latent heat release heats the atmosphere! surface and causes more
04/25/2022
AHS 104 Day 40 Spring 2022
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It rains more!
evaporation!
Global warming hypothesis: humans are
influencing the climate
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How?
◆ The concentration of greenhouse gases is
increasing.
◆ This is enhancing the greenhouse effect, making
it warmer!
Do we have evidence of an increase in greenhouse
gases?
04/25/2022
AHS 104 Day 40 Spring 2022
7
CO2 measurements
Current level
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At Mauna Loa,
Hawaii
Was ~280 ppm
before industrial
times
Increase due to
human production
04/25/2022
AHS 104 Day 40 Spring 2022
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Measurements
taken from high
Northern
latitudes to the
South Pole
All show same
upward trend.
Notice larger
seasonal cycle
in NH
measurements
04/25/2022
AHS 104 Day 40 Spring 2022
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Not all CO2 goes into atmosphere
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About half of emissions are absorbed by oceans or
taken up by plants (photosynthesis)
The other half, however, has a very long residence
time
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Because of the long amount of time that carbon dioxide
remains in the atmosphere, some impacts are locked in,
perhaps for centuries to come
04/25/2022
AHS 104 Day 40 Spring 2022
10
Here’s how much carbon has
been added to the atmosphere
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AHS 104 Day 40 Spring 2022
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CH4 (methane) measurements
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AHS 104 Day 40 Spring 2022
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Chlorofluorocarbons (CFCs)
Smallest amount
of gas, but very
efficient
greenhouse gas
• Worldwide reduction beginning in 1980’s, because they were
the primary cause of ozone depletion in the stratosphere
• Lingers in stratosphere for years, but reductions now being seen
04/25/2022
AHS 104 Day 40 Spring 2022
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Summary: anthropogenic
greenhouse gases and their trends
Carbon dioxide (CO2 )
◼ Flourinated gases like CFCs
◼ Methane (CH4 )
◼ Nitrous oxide (N2O )
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In order of relative importance.
04/25/2022
AHS 104 Day 40 Spring 2022
14
Back to our global warming hypothesis
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Do we have evidence of an increase in greenhouse
gases?
◆ Yes, the preceding slides make this clear.
So, we have increasing global temperatures and
increasing greenhouse gases.
04/25/2022
AHS 104 Day 40 Spring 2022
15
Global Warming Theory
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This doesn’t prove that our hypothesis is correct; it
just elevates it from an hypothesis to the status of
a “theory” worth testing
Our theory must provide testable predictions so
that we can determine if it is of value
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AHS 104 Day 40 Spring 2022
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Elements of a Scientific Theory
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Fits or ‘explains’ current observations or
experiments
Makes testable predictions about something that
can be measured
Doesn’t require ‘special cases’ to explain certain
data = simpler is better
Results must be reproducible!!
Note: It is impossible to prove a theory is correct
because you can’t anticipate all future tests.
04/25/2022
AHS 104 Day 40 Spring 2022
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Global Warming Theory
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As we saw, a good theory is testable.
◆ If it passes the test, we gain confidence in it.
◆ If it fails the test, we must correct it or discard it.
How can we test the global warming theory?
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AHS 104 Day 40 Spring 2022
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How can we test the theory?
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We would like to make a comparison: Look at the
climate on our Earth (with its anthropogenic
GHGs) vs. Earth2 (with no anthropogenic GHGs)
Can’t do this classic kind of experiment: we don’t
have another Earth!
Our Earth
04/25/2022
Earth2
AHS 104 Day 40 Spring 2022
19
Climate Models
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We’ll have to make a simulated Earth: need a
computer model
These models are like Numerical Weather
Prediction models
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They predict variables at millions of grid points through
out the atmosphere and ocean
They are coupled atmosphere-ocean models so
they simulate the dynamics of the oceans, too
But they are less sophisticated on the treatment of
the weather
04/25/2022
AHS 104 Day 40 Spring 2022
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Who’s doing the predictions?
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Many research labs around the world
Several different models (~20)
Coordinated by the IPCC
◆ Intergovernmental
◆ Panel on
◆ Climate
◆ Change
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AHS 104 Day 40 Spring 2022
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Results of climate modeling
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So what are the computer predictions?
◆ We’ll look at this in detail next week!
04/25/2022
AHS 104 Day 40 Spring 2022
22
Question 1 (1 point)
The theory of global warming says that human activities are the cause of the
observed increase in the average global temperature over the past 150 years or so.
True
False
Question 2 (1 point)
A scientific theory must:
fit the observations
оо
be testable
be reproducible
all of the above
Question 3 (1 point)
All carbon dioxide resulting from human activities ends up in the atmosphere.
True
False
Question 4 (1 point)
A way to test the theory of global warming is to use computer models of the climate.
True
FalseQuestion 5 (1 point)
The gas producing the largest greenhouse effect is
carbon dioxide
water vapor
carbon monoxide
hydrogen
Question 6 (1 point)
Which is an anthropogenic greenhouse gas?
carbon dioxide
methane
chlorofluorocarbons
all of the above
Question 7 (1 point)
Which one of these is the most important anthropogenic GHG in terms of
influencing the climate (the one that is currently increasing the most)?
carbon dioxide
methane
chlorofluorocarbons
nitrogen oxides