A great piece of science journalism

I really enjoyed this New York Times article about scientists measuring the melting of Greenland's ice sheet.  It has so many great elements:

beautiful images and video. We often think of science as complicated and abstract, but the beauty of nature is what drives a lot of us to keep at it.  Capturing our work with a beautiful image is a worthy goal for scientists who want the public to be able to relate to their work.  In this article, the images and video are especially well integrated into the text, rather than standing apart from it.

the whole story of the research.  Too often we see just the final result, but this article explains so much more: why the team thinks the research is worthwhile, how they got funding for it, how hard they work, and how persistent and creative they are at problem-solving in pursuit of their measurements.

scale: this is one of the most difficult things for scientists to convey.  This team is measuring the melting in one small part of the ice sheet, but with the hope of extrapolating to the entire ice sheet.  The article literally zooms in from a view of all Greenland to a view of the campsite, and then---very importantly---zooms us back out to see the big picture again.

we practice thinking scientifically. Even those who are quite familiar with the basics of global warming and sea level rise will learn an important nuance: models of ice melt are far cruder than the reality.  The greater the extent to which these rivers flow under the ice sheet, the faster we may lose the ice sheet and get truly substantial sea level rise.  These measurements will help us improve the model and therefore the forecast.  This article also shows how good scientists withhold judgment until the facts are in: although massive ice loss is an alarming prospect, the team "might even learn...that the water is refreezing within the ice sheet and that sea levels are actually rising more slowly than models project."

Good job, NYT!  This is a model for science journalism.

Climate 101B: Uncertainty and Model-independence

Following up on my previous post, a few more points are worth making
regarding the scientific process.

First, regarding uncertainty.  Earth's atmosphere and oceans do form a
more complicated system than the simple model I described.  For
example, here's one way in which it is possible that temperatures
would not rise much in response to carbon dioxide impeding the outward
flow of heat.  When temperatures go up initially, that means more
water vapor in the atmosphere.  If that water vapor condenses into
clouds, the extra clouds could reflect enough sunlight back into space
to reduce the heating and make temperatures fall back to normal.  This
mechanism would act like a thermostat keeping Earth's surface within a
narrow temperature range, and we wouldn't need to worry about keeping
our carbon emissions in check.  So, if you heard Arrhenius's warming
prediction in 1896, you could easily say, "but there's a lot of
uncertainty in that prediction because we don't understand cloud
formation.  Maybe there won't be that much warming.  It's uncertain."

The point I want to make is that uncertainty cuts both ways. Water
vapor is itself a greenhouse gas, so if the extra vapor does not
condense into clouds, the greenhouse warming will be accelerated.
Yes, the prediction is uncertain....but that means that more extreme
outcomes, as well as less extreme outcomes, are possible.

If a little bit of warming produces clouds which shut down further
warming, we would call that a negative feedback loop; negative because
any change contains the seeds of its own reversal.  If instead a bit
of warming creates water vapor which accelerates the warming, we would
call that a positive feedback loop; positive because a little movement
encourages further movement in the same direction.  One reason climate
is complicated is that it is full of feedback loops, another example
being that reduced ice coverage causes more sunlight to be absorbed,
which reduces ice coverage further, etc.  So what's the verdict on the
cloud formation?  We still don't know; it may depend on how much
small-particle pollution we produce, because these small particles
provide the seeds for cloud condensation.  But meanwhile, temperatures
keep rising.  So while we puzzle over the details, let's not forget
the big picture: we keep making Earth's carbon-dioxide blanket thicker
and thicker.

Second point: I've repeatedly stressed the important of models in terms of
understanding a system. Models are great for exploring a variety of
scenarios, but is there anything we can say about climate that does
not depend on what model we adopt?  Such model-independent statements
can be valuable anchors when we're not sure which model to adopt.  I'd
like to focus particularly on a (more or less) model-independent
statement regarding sea levels.  We can get rid of models and just
accumulate data regarding sea levels and carbon dioxide levels in the
past, and then we can simply ask, what is the typical sea level when
the carbon dioxide level is 400 parts per million, as we have now
caused it to be? (It's up from about 275 before the Industrial
Revolution.)

The answer is shocking: 24 meters, or 80 feet!  Go ahead and play with
this interactive flood map to see what such a rise will do to your
state or country.

Now I have to give a few caveats. First, changes in carbon dioxide
concentration and sea levels occurred very slowly in the past.
Although we are pumping carbon dioxide in very quickly, it's quite
likely that it will be hundreds or even a few thousand years before
the effects of the carbon input are fully realized and sea levels rise
this much.  Essentially no one is predicting these sea levels within
our children's lifetimes.  But still....this will be a lot for our
great-great-grandchildren to deal with.  And yes, there's uncertainty on this
prediction. Sea levels may rise less than this.  But they may also rise more
than this.

Second caveat: this prediction is not entirely model-independent. To
be an extreme devil's advocate, if CO2 levels in the past were somehow
a natural effect of higher sea levels rather than a cause, then we could not
use past data to predict what would happen when we artificially increase
CO2 levels today.  To be clear, I invoke that scenario not because I
believe it, but simply to highlight how an apparently
model-independent statement is often not entirely
model-independent. If all kinds of crazy models are allowed into the
discussion, then very few truly model-independent statements can be
made.  But within the scope of "reasonable" models, we can say that
sea levels will rise by around 24 meters; we just don't know long
that will take.  Predicting how long it will take requires a model!

If you are interested in further reading, start with this Skeptical
Science post, which summarizes this publication in an approachable
way.  Skeptical Science, by the way, is a good resource for rebutting
common climate myths.

Climate 101

Nice article today in the New York Times: Study Links Temperature to a 
Peruvian Glacier’s Growth and Retreat. It's a good example of how news
about climate change could easily be misread as indicating more doubt
than there really is.  The headline makes it sound as if the link between
glaciers and temperature is so tenuous that this is the first evidence of it,
and that it has been established for only one glacier.  The truth is very
different, even though the headline and article are not wrong once you
understand the context. This post is aimed at helping teachers
and students with the basics, and then use that to parse the news.

Over a century ago, it was known that carbon dioxide impedes the flow
of heat (in the form of infrared light) from the Earth out into space,
while not impeding the flow of heat (mostly in the form of visible
light) from the Sun to the Earth.  If not for this natural greenhouse
effect, Earth would be much colder.  Teachers can demonstrate quite
directly that carbon dioxide impedes the flow of infrared light, but
many teachers may not have the right equipment.  Here's a video
comparing the temperature rise of two bottles, one with elevated
levels of carbon dioxide and the other with standard air.  And here's
a nice video using an infrared camera to show quite directly that
infrared light is largely blocked by carbon dioxide.

Around the same time (1896) Svante Arrhenius recognized that humans
were pumping ever more carbon dioxide into the atmosphere, and that
this would lead to warming.  But "warming" sounded reasonably
beneficial, especially given Arrhenius's prediction that it would take
place slowly over thousands of years.  Arrhenius did not account for
the large increase in population over the ensuing century, nor for the
large increase in per-capita use of fossil fuels (cars, airplanes,
etc). Worldwide, we now emit about 17 times the carbon dioxide emitted
in 1896, so change is coming much faster.  And now we know that an
increase in temperature is not as beneficial as it may sound because
it can radically change weather patterns, which imposes large costs on
humans as well as on many species which cannot move and adapt rapidly
enough.  Apart from that, Arrhenius deserves kudos for his prescience.

Yet if we heard this prediction in 1896 we would be justified in
expressing some skepticism. Earth's atmosphere and oceans (where most
of the excess heat is deposited) form a complicated system, and the
response of a complicated system to a simple input (more heat) may
well not be a simple result (higher temperature).  But healthy
skepticism goes only so far; unless you have a better model, you have
to admit that the best model predicts warming.  Just saying "it's a
complicated system" does not give you the right to reject all models.
In this case, you would have to figure out where the extra heat would
go without causing increased temperatures, and you would have to have
some evidence to motivate belief in that model.

Fast forward to 2014.  Warming is here, and we've learned a lot about
climate models in the meantime. We did find complications (El Nino,
for one), but the simple model was reasonable in its overall
prediction.  More heat does mean a higher temperature.

One way "climate skeptics" (I put the term in quotes because
oil-company funding leads to a kind of "skepticism" different from the
detached sort of skepticism we encourage in science) sow doubt about
this result is to suggest that the warming may be due to natural
cycles.  There certainly are natural climate cycles, but rather than
treat them in detail here I want to make a bigger point about how
science works: When a model makes a prediction and the prediction
comes true, we should gain confidence in the model, and we should lose
confidence in models which made contrary predictions. Yes, it's
conceivable that the greenhouse model's prediction came true through
a fluke of natural cycles rather than accurately modeling how nature works
...but how much confidence would you put on that possibility? 

A prediction is a powerful thing, so let's note the distinction between
a prediction and a retrodiction (or postdiction), which is when you make a
hypothesis after looking at the data.  Using data (rather than laws of
physics or other guiding principles) to generate hypotheses is a fine
thing to do, but because "patterns" can randomly appear in data you
cannot confirm the hypothesis with the same data which generated it;
you must seek out new data. (Admittedly, even scientists sometimes
forget to apply this principle.)  Climate skeptics can suggest
alternative causes for the warming after looking at the data, but we
should have much more confidence in the model which actually predicted
the data.

Now, the news: a reconstruction of the timeline of growth and
shrinkage of a Peruvian glacier shows that shrinkage is most highly
correlated with temperature and not with other factors such as
precipitation.  You have to get halfway through the article to get the
background:

land ice is melting virtually everywhere on the planet...the pace seems to have accelerated substantially in recent decades as human emissions have begun to overwhelm the natural cycles. In the middle and high latitudes, from Switzerland to Alaska, a half-century of careful glaciology has established that temperature is the main factor controlling the growth and recession of glaciers. But the picture has been murkier in the tropics. There, too, glaciers are retreating, but scientists have had more trouble sorting out exactly why. 

So, you may have started reading the article thinking that scientists
understood very little about glaciers if they were just now finding a
"link" between glacier shrinkage and temperature, but you now see
that a lot of important knowledge has already been established.
Newspaper articles are designed to tell you what's new first, so it's not
the writer's fault that this background was buried deep in the article.
Nevertheless, in practice many readers will just read the headline and
skim the first part of the article, thus missing this crucial background.
Teachers and students should be aware of this when reading science news.

But wait, there's more! The article goes on to explain how the details
of tropical glaciers are different from most glaciers (intense
sunlight can vaporize the ice directly, and the sunlight lasts
year-round) but that one group of scientists has studied the matter
and still concluded that temperature is the driving factor in
shrinking tropical glaciers. "But a second group believes that in some
circumstances, at least, a tropical glacier’s long-term fate may
reflect other factors. In particular, these scientists believe big
changes in precipitation can sometimes have more of a role than
temperature."  In other words, this is a legitimate scientific dispute, but
it is about the details of a very specific type of glacier and has little or
nothing to do with overall concerns about glaciers (or sea ice)
melting worldwide, much less about the reality of climate change.  Yet
someone who wants to sow doubt about climate change can point to this
and say "scientists don't really understand why glaciers melt" and people
who don't read the article carefully may well be snookered by that.
Please make sure you (and, if you are a teacher, your students) don't
get snookered.

My next post discusses two more aspects of the nature of science---uncertainty
and model-independent statements---in the context of climate.

One Percenters

We've been bombarded all winter with stories of cold and snowy weather in the eastern US, but the news was just released that January 2014 was the fourth-warmest January on record.  How can this be? The eastern US covers less than 1% of the Earth's area, so (as this essay nicely puts it) "if the whole country somehow froze solid one January, that would not move the needle on global temperatures much at all."  That essay is worth reading because it goes on to explain how subjectively people do perceive global warming: something as unrelated to global warming as being in a cold room does have an influence on the opinions voiced in a survey.   Educators should be aware of this, and actively work on making students think objectively and use data.

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.