On Radiometry and Climate Change

We Have Cause to be Skeptical

I think that a healthy but open-minded skepticism is generally a good thing.  Open-mindedness without any skepticism results in one's brain falling out of his head (to paraphrase Richard Dawkins), while an impassive skepticism without some intellectual flexibility results in an obstinate and stubborn jackass.  Neither is a desirable state.

I discover a great many jackasses who feel that they need to expose the falsehood of global climate change, especially during the winter when every big storm is apparently proof positive that the theory is false.  Just watch Fox News for examples.  Now I would not mind listening to this debate if it were actually taking place between scientists.  But it is organized in a conspicuously lopsided fashion: 97% of scientists say the climate is changing (and we are probably causing it), while it is almost entirely non-scientists who say it isn't (or at least that it's part of a "natural cycle").  Professional jackass Greg Gutfeld of Fox's The Five has described global warming as "basically dead."  For brevity, I will refer to those who dismiss claims of global climate change as hoaxers.

Why this disparity?  There are all sorts of non-scientific influences that shape our views of physical reality, which I don't care to go into.  Let us suffice by saying that hoaxers just don't know the science and have skepticism toward any belief that fits into their "liberal" schema.  They are especially ignorant of the key evidence that unequivocally supports the proposition, "Global climate patterns are changing, and really quite rapidly.  We're changing them."  Hoaxers seem to fixate on solely the temperature aspect, as though some effeminate scientist in a woolly sweater-vest simply steps out of his office each afternoon, sticks a thermometer in the air, and says, "By George, it's a little warmer today."  Let's get to the evidence.

The Hardest Evidence

In a recent post ("On Radiometric Dating and the Age of the Earth") I discussed how scientists use radioisotopes to determine about how long ago the owner of an organic sample died, or how long ago a piece of rock was molten.  Recall that we can indirectly "count" the ratios of certain isotopes by using a sensitive Geiger counter, or better yet, a gas-chromatograph mass spectrometer (with exquisite precision).*  This method, snappily named radioisotope analysis, has been verified as reliable and accurate since about 1905, when physicist Earnest Rutherford invented it.  One hundred and eight years of critical evaluation and use is not exactly dabbling, and no serious, educated scientist doubts its value and precision (although the interpretation of specific results is always up for criticism.  Just look at the discussion surrounding the Shroud of Turin).

So radiometric analysis of isotopic ratios works.

Let's go to the antarctic.  If you set foot on the south pole, you'd be standing on about 2 or 3 kilometers of glacial ice.  Imagine digging straight down with a very expensive auger and pulling out a tube of ice.  If you look closely, you can make out distinct layers of varying opacity and transparency, and even a layer of soot or smudgy brown here and there.  Each of these layers represents a season, and you can literally trace your way down through history by counting the layers, as in the black-and-white photograph below of a sample taken from 1838 meters deep. (Occasionally the layers mash together and you can't tell them apart anymore except chemically.)

Image source

Image source

The Theory Behind Ice-Cores

Now here's the really fascinating thing about glacial ice.  It has water in it.  Water, as you know, is made of two hydrogen atoms and one oxygen atom in the middle.  Oxygen comes in one common isotope, O-16, and two rare isotopes, O-17 and O-18.  O-18 is just a touch heavier than O-16, by two atomic mass units, to be precise.  O-18 is heavier by a great enough degree that the physical characteristics of the water it makes up are actually a little different: the water is denser and requires more energy to vaporize.

Suppose you and a friend were holding a bowling ball and a volleyball, respectively.  If you both tried to shake the balls as fast as you could, you'd find that your friend can shake it a lot faster, with the same amount of energy.  It's like that with water molecules that have O-18; they take more energy to shake up, so they require more heat energy to vaporize.  Follow?

Now your water mixture of H2O-16 and H2O-18 is floating around as vapor in the atmosphere.  As the water finds its way to glaciers and the poles, it often condenses into clouds, which then make some snow.  On the way to the poles, the H2O-18 is preferentially precipitated out into the oceans and continents as rain, especially if the average atmospheric thermal energy is low (it's cool).  But when it's warm, the H2O-18 can stay aloft for longer, because there is more energy to keep it as a vapor.  So in warmer periods, the glacial ice has relatively more heavy water (H2O-18) than it normally would.  (Keep in mind that H2O-18 always represents a very tiny fraction of glacial ice, around 1%.  But that tiny fraction fluctuates with the average thermal energy, or heat.)

In ocean cores we actually see the opposite relationship.  Since in cool periods O-18 is preferentially precipitated out of the atmosphere before it gets to the poles, that water rich in O-18 ends up in the oceans and eventually in the layers of sediment that form carbonate rocks on the ocean floor.  We can measure the isotopic composition of the layers and find that their ratios of O-16/O-18 are inverse to those of glacial ice.  The nice thing about ocean cores is that they go back to around 500 million years, while the furthest we've gotten with ice cores is around 1 million.

I know the last paragraphs were dense and you have to follow them carefully to see what is going on.  But the kicker comes next: We can measure the fraction of O-18 that is present in glacial ice.  We have compared that fraction with known average global temperatures (these are known because we physically measured and recorded them).  And we find... wait... wait... wait... We find that there is a shockingly reliable correlation between O-18 percentages and the average global temperature.  Higher temperature, more O-18.

Extrapolate these data backward in time as far as you care to go, and we find that in the last two centuries... wait... wait... wait...O-18 percentages have risen far faster than would "naturally" be expected.  And they even correlate quite nicely with carbon-dioxide percentages.  We know this because atmospheric gas bubbles are trapped in each layer of the ice, and we can also measure the composition of the gas a mass spectrometer.

You can find articles explaining the methods and interpretations of this work at NASA, the Journal of Geophysical Research, the Earth and Planetary Science Letters, and some publication called Nature.

The Evil of the Double-Standard

I can hear what a balking hoaxer is saying already.  "Of course those publications are going to say global warming is happening- they're written by scientists!  All scientists are in on it."

Yes.  Scientists all say that because they know what the hell they are talking about.

This is like saying, "Of course that professor of mathematics is going to say that six times six is thirty-six.  All mathematicians say that."  Can you see how idiotic this sounds?

Analysis of radioisotopes from ancient glacial ice is not simple or easy.  It takes expensive machinery and very, very, careful methods.  There are all sorts of pitfalls that can lead to bad analysis or bad conclusions.  This is the case in very nearly every science.

What upsets me and makes me feel like my description in my first blog post, is that this discussion takes place most fiercely among non-scientists.  What astonishing hypocrisy.  A hoaxer can dismiss the possibility of climate change with such true smugness, that it causes my fists to clench and they start wanting to punch something.  If the evidence were inconclusive or disproved climate change, scientists would say so.  

Scientists are not really known for being stupendous liars or conspiracy theorists, and I wish they they were just a little more respected by American non-scientists.  The work of chemists, physicists, astronomers, engineers, ecologists, nuclear physicists, pharmacologists, and all sorts of other scientists are rarely regarded with such scrutiny and criticism by the public.  Why the obvious double standard for climate scientists?  As I have said, the reasons for skepticism from a science-illiterate public are too varied and diverse for the scope of this blog entry, but the double standard irks me to an almost painful degree.

Go here for an outstanding over-view on climate change denial, which I may discuss in a future blog post.

Look for double standards and try to expose them; they are the root of much ignorance in this debate.

* Mass spectrometers are used to test professional athletes for illegal steroid use.  Steroids are made in the body from cholesterol, a carbon-based honey-comb shaped molecule that helps cell walls retain their structure.  It turns out that steroids produced naturally in the body have a very, very predictable ratio of C-12, C-14, and C-13.  The steroids produced by pharmaceutical companies are made (accidentally or deliberately) in different ratios.  Analysts look for anomalies in the C-13 ratio of human steroids to see if the number is inconsistent with what is natural.  When it is, the odds of a false reading are something like 1 to 10,000,000,000,000,000,000,000,000,000,000.  That's astronomically small.  This article on isotopically labelled steroid assays explains how false readings can happen.