Climate Change

Yesterday we tied together California (Grade 6) Science Standards 6
(resources), 3 (Heat), and 4 (Energy in the Earth System).  We'd
already done quite a bit of 3 and 4, so we started with a discussion
of resources.  The consequences of using resources (6a) led naturally to
the greenhouse effect, which builds on our previous understanding of
heat flow in the Earth-Sun system.  We had previously calculated a
rough temperature that Earth "should" be at, ie the stable temperature
at which Earth should radiate just as much heat into space (in the
form of infrared light) as it gets from the Sun (mostly in the form of
visible light).  This temperature was just below freezing, and it
turns out that a natural greenhouse effect makes Earth livable.

We started with this video, which is a nice short demo of how carbon
dioxide absorbs infrared light.  C02 is by no means the only
greenhouse gas; water vapor is also very important, and methane
absorbs much more infrared light on a gram-for-gram basis, but there
is not enough methane in the atmosphere to make it the most important
greenhouse gas overall.  We also watched a short clip of another
video, which demonstrated how the temperature of a bottle of carbon
dioxide increased more than a bottle of air when both were heated by a
lamp.  This latter experiment requires only basic equipment and a
teacher might consider having the kids do the experiment, but I
suspect the experiment could be finicky in real life: you will have to
make sure there are no leaks in the C02 bottle, etc.

The kids were ahead of me on this one. They had already made the leap
to climate change, but I wanted to do at least a quick review to fill
in the logic.  The atmosphere is basically transparent to visible
light, the form in which we get energy from the Sun; if it's not
transparent to infrared light, the form in which Earth gets rid of its
heat, then Earth must heat up.  As stated above, we need a certain
amount of natural greenhouse effect to avoid freezing over, but there
can be too much of a good thing.  We spent the rest of the time in
small groups, playing with a computer simulation of all this. This
simulation is really good, so I encourage you to click Run Now (it
takes a minute to load and start).  You can adjust the level of
greenhouse gases from none (to see our previous calculation in action)
to lots.  As I circulated around the groups, we discussed the effect
of clouds (keep us cooler during the day but warmer at night) vs
greenhouse gases (always keep us warmer).  We also looked at the
Photon Absorption tab, which shows what's going on microscopically.
You can shoot visible or infrared photons (the smallest unit of light)
at a variety of molecules to see which are greenhouse gases.  In the
main (Greenhouse Effect) tab, the view is too zoomed out to see what
the photons are interacting with when they bounce around.  This was a
successful activity: students learned something as they explored, and
some students worked into their recess break to finish answering the
questions on the worksheet.

(Maven alert: it's common to say that greenhouse gases "trap" heat,
but this is not technically correct. It's more accurate to say that
they impede the flow of energy.  I didn't correct the kids when they
said "trap", but teachers should be aware of this.  Saying "trap" as a
teacher leaves you open to refutation.)

After the recess break, we discussed feedback loops and the
physics/engineering definition of positive and negative feedback
(which have nothing to do with psychological concepts such as negative
reinforcement or positive attitude).  I asked them to classify 11
different situations as positive or negative feedback (eg, foxes
provide negative feedback on the rabbit population), and they did very
well, so the concept is possibly less challenging than I imagined.  We
briefly discussed how confusing it is to have delayed feedback (eg
Alice says something to Bob and three days later he raises his voice).
Psychological experiments have shown that when feedback is delayed a
long time, people get very confused as to what causes what: they think
their actions have no effect, or the opposite effect.  (For more on
this, I recommend the book The Logic of Failure.)

So it is with climate change.  Scientists knew of CO2's heat
"trapping" properties more than a century ago and predicted rising
temperatures as we dumped more CO2 into the atmosphere, but it takes
so long for the heat to build up that it's easy to ignore.  By the
time we really see the temperature rise in a very convincing way, we
have dumped so much C02 into the atmosphere that temperatures will
rise much more even if we take immediate action.  Compounding this is
variability: if you just pay attention to the temperatures in your
neighborhood, there is so much variability from day to day and season
to season that it's impossible to notice a change in the average
temperature.  To see the change, you have to average together many
thousands of temperature measurements.

Even after getting people to accept that line of reasoning, they will be
unimpressed by the global average change so far: 1.4 degrees Fahrenheit.
What's a degree or two between friends?  But the change has been much
larger in some regions (the Arctic) and even 1.4 degrees results in a lot of
dislocation and expense: species have to adjust their ranges all over the world,
malaria may be able to move further from tropical regions, etc.  Won't Canada
and the northern US be happy to be a little bit warmer? Maybe, but it's not that
simple. Rain patterns may shift, so farmers in Canada may not be so happy after
all.  And northern forests are being destroyed at a rapid rate now that certain
kinds of beetles can survive the winter further north; beetles are mobile, but trees
are not, and the northern trees will be destroyed before they have time to
adapt to the beetle.  And areas which do gain from climate change may
be overrun with refugees from areas which lose big-time.

Anyway, the delayed-feedback idea led into the carbon cycle.  Over
tens of thousands of years the carbon cycle will remove excess carbon
from the atmosphere, so the Earth will not get hotter without limit
(thus answering an earlier question from a student). 

Our final activity was looking at this interactive flood map.  Seas
rise because the ocean heats up and expands (a very slow process) and
because of melting glaciers (not as slow, but still not easy to
predict).  The standard prediction for the year 2100 (when these
students will be old, but quite possibly still alive) is about 1 meter
of sea level rise, so I asked the students to dial in 1 meter and
answer a few questions about impacts on their house and on nearby
areas.  But the slowness of the ocean expansion means that the impact
of the current amount of carbon is further down the road, and has been
estimated to be 21 meters.  So I asked the students to dial in 21
meters and answer a few more questions.  This was another successful
activity combining student exploration with learning; I urge readers
of this blog to try the interactive flood map as well. Twenty-one
meters seems insane, so some kids need to be reassured that it will be
slow, over hundreds of years and perhaps a thousand years, so people
will have time to evacuate and adjust.  Still, evacuation and
adjustment are costly financially and emotionally so it may be better
to prevent the need for so much evacuation and adjustment in the first
place.

I didn't have time for a few things I wanted to show, but I can link to them here.
First, a quick Google image search for "glacier comparison" shows how fast most
glaciers are melting.  It is astounding*.  Second 30 seconds from this story about the
documentary Chasing Ice provide another dramatic look at glacier melting. (Sorry,
you will probably have to watch an ad to see this, but I couldn't find a better link.)

P.S.: Another important point for teachers of this subject is to emphasize that
"global warming" doesn't mean "every part of the Earth warms all of the time."
There is a model behind the predictions, a model with moving parts which affect
each other so that the predictions are richer than a novice imagines. For example,
a warmer atmosphere will also be a more humid atmosphere, so many areas will
get more precipitation and more intense storms.  If you live in a place where it's
cool enough to snow occasionally, then yes, global warming predicts that you can
get more snow.  People who think a big snowstorm contradicts predictions of
climate models simply haven't taken the time to get familiar with what climate
models really predict.  A scientific model should make a rich set of nuanced
predictions: that makes it easier to set up stringent experimental tests of the model.
This nuance does mean that scientists must work harder to educate the public.  If
any scientists are reading this, I plead with you to put in that hard work.  Society
needs you.

*Climate change deniers have recently made a big deal about a study showing that glaciers in some parts of the Himalayas are actually growing.  Note the qualified phrase "some parts of the Himalayas."  This is NOT what's happening to most glaciers around the world.  As noted above, climate change may have some "winners" as well as losers.  But I doubt the "winners" will feel very secure with so much dislocation in the world.