Fingerprinting Carbon Dioxide

For the past two centuries, the amount of carbon dioxide in the atmosphere has been rising from 280ppm to over 390ppm in 2010. This is an incontrovertible fact. What has been called into question in recent years is the source of this carbon dioxide; it has been asserted by some that humanity is not responsible for this increase. Yet this position not only makes no sense, it is easily disproved.

The first line of evidence is what most people are aware of. The logic is straightforward: Humanity has been burning large amounts of fossil fuels for energy for the past two centuries. The burning of these fossil fuels releases carbon dioxide and other greenhouse gases into the atmosphere. Over the same time period, atmospheric levels of carbon dioxide have risen by exactly the same amount as has been released by fossil fuel burning. Therefore, the burning of fossil fuels is responsible for the rise in carbon dioxide. QED.

However, this is not enough for some people; they want more evidence. Climate scientists were happy to oblige. But before I can get into two further lines of evidence, I need to review some high school chemistry.

All atoms are made up of protons, neutrons, and electrons. Protons have a positive charge, neutrons no charge, and electrons a negative charge. The number of protons and electrons determines what element the atom is. For example, oxygen always has 8 protons and 8 electrons. If it had 9 protons and 9 neutrons, it would be fluorine. However, while atoms must always have the same number of protons and electrons, the number of neutrons can vary. With oxygen, most atoms have 8 neutrons. However, a small percentage of atoms have 10 neutrons. These different versions of an atom of the same element are known as isotopes.

The element in question with global warming is carbon. The most common isotope of carbon is 12C, which has 6 protons, 6 neutrons, and 6 electrons. This isotope accounts for 98.89% of all carbon on Earth. A second isotope is 13C, which has 6 protons, 7 neutrons, and 6 electrons and accounts for 1.1% of all carbon on Earth. And finally, there is 14C, which is made up of 6 protons, 8 neutrons, and 6 electrons and is only a tiny fraction of all carbon on Earth.

These isotopes matter because fossil fuels are depleted in 13C and 14C. Thus, we can predict that, if fossil fuels are the reason carbon dioxide levels in the atmosphere have risen, the atmospheric concentrations of 13C and 14C must both be falling. But why are fossil fuels depleted in these isotopes?

To explain 13C, we have to remember that coal is made when dead plants do not decay. This is significant because, during photosynthesis, plants process carbon and the isotope of that carbon matters. Plants “prefer” 12C to 13C because 12C is easier to process. Therefore, plants have a smaller percentage of 13C than is found in the environment. This means that coal is also depleted in 13C.

14C is very different. This isotope is significant because it is radioactive, meaning that it decays over time. Every 5,730 years the amount of 14C present is halved. This means that fossil fuels that are millions of years old will have no 14C left.

So what does the data tell us? Below are graphs of the concentrations of 13C and 14C respectively.

As you can see, the concentrations of both isotopes have been decreasing. There is no other possible explanation for this than that the burning of fossil fuels has caused the rise in carbon dioxide in the atmosphere over the past two centuries.

7 Responses to Fingerprinting Carbon Dioxide

  1. JoeS says:

    By “concentration” I assume you mean the percentage of all CO2 in the atmosphere? Can you relate the concentration percentage drop to the overall CO2 percentage increase over a time period.

  2. Lynne says:

    “14C is very different. This isotope is significant because it is radioactive, meaning that it decays over time. Every 5,370 years the amount of 14C present is halved. This means that fossil fuels that are millions of years old will have no 14C left.”

    This is you assuming that the climate deniers will at least agree with you that the earth is millions of years old. Big, big assumption!

    Second thing a denier will say: “but, how did we measure CO2 and isotopes in the 1700s and 1800s?? They didn’t even know about atoms then!”

    Of course, I know the answer, at least in part, but honestly, this is the level of thinking of these people. Never mind that the bubbles trapped in ice in the Antarctic have allowed us to measure the atmosphere going back tens of thousands of years. They just won’t believe you.

  3. Lynne says:

    Oh and don’t even bother to start down the road to the fact that we should be in a cooling period (relatively) possibly going into a mini ice age, if our tens of thousands of years of measurements are correct, and that when we started burning fossil fuels in the Industrial Age, we should have been at or near the very top of the mid-ice-age warmth level and heading back down. Therefore, with all the warming since then, we’ve been going far above peak for an inter-ice age period. VERY unnatural.

    I like to explain global warming as the following: first, I ask a question: do you remember, that when you learned about the dinosaurs, you found out the earth was warmer, and the big dominant species at the time were cold blooded – able to survive even though they cannot make their own warmth? So picture a CO2 rich world…warm, tropical over much of the planet. HOT even. Then picture hundreds of millions of years of plants and animals being buried in the ground. Plants and animals which are make of a lot of carbon. That carbon got locked in the earth, and over millions of years, the earth slowly (VERY slowly) cooled, as more plants/animals got buried. Mammals took over, and survived ice ages, cold blooded animals are stuck in the tropics, etc.

    Then apes came along, and evolved into humans. Relatively recently, in geological terms. We evolved in a world that was much different than the ones the dinosaurs lived in, a cooler world.

    Then came the last couple of centuries, and the discovery of coal and oil. The industrial revolution. Humans start digging up the locked carbon in the earth that was put there and compressed over tens of millions of years. We start to burn the carbon – a LOT of carbon, in the last 50 years – that was locked in the earth for so long. Burning it releases it back as CO2.

    We humans are returning the earth to what it was like millions, maybe tens of millions, maybe even hundreds of millions of years ago. Back when mammals had a bad time of it and cold blooded animals could live almost anywhere.

    Sometimes, when I tell this simplified story which explains carbon locking etc, I’ve seen a light bulb come on in their heads. I’ve never really gotten a true denier to listen to the story, but people who didn’t *quite* understand the fuss about global warming have suddenly realized, hey, it’s simple math! Lock it in the ground over millions of years, super-slowly cooling planet. Unlock and burn it, rapidly returning to a hotter, nastier planet that has not existed since dinosaurs. They *get* it.

  4. Andrew says:

    Technically, it’s the percentage of all carbon in the atmosphere. Carbon and carbon dioxide are used somewhat interchangeably, which causes a lot of confusion. The reason for this is almost all carbon in the atmosphere is in the form of carbon dioxide. So the measurements are of carbon.

    For 13C, the relevant measure is the ratio of 13C/12C. Since 1850, this has fallen by 0.15%. For comparison, a transition over several thousands years from an ice age to no ice caps has a change of 0.03%. That translates into something like 1.09% of carbon, instead of the expected 1.1%. I know that seems small, but it’s about 5.5 GT worth of carbon dioxide, meaning about 1.5 GT of carbon.

    14C is a bit more difficult. The reason the graph ends at 1950 is that atmospheric tests of nuclear weapons released relatively large amounts of C14 into the atmosphere. By 1954, the ration of C14/C12 had fallen by about 2% relative to 1850.

  5. Andrew says:

    Lynne, this is less for the deniers, who I doubt will ever listen to scientific evidence as they have thus far behaved like creationists, but for the people who want to actually understand the problem.

    You’re getting ahead of me lol. I’m not done explaining the background information; I’ll get into the paleoclimate data after Christmas.

  6. Shawn says:

    I guess the real question is.. so what?

    The earth is big.. and balances itself out.

    More C02 means plants bloom to handle much of it, as does the ocean algae (wasn’t it shown recently that this was not taken into account in that UN report?)

    If water rises over time.. people will move. animals will move.. it happens.

    Heck, big parts of Boston are on landfill now and never should have been populated. People worked it out.

    Who knows, maybe Dracut will attain oceanfront status.

    I heard about the ozone layer 30 years ago from the environmentalists. We’re supposed to all be dead now. Then came global cooling. Then the rain forests. Then the “loss of thousands of species per year.” Then the baby seals.

    Ya know, its the same people, who seem to profit off of all these crises, who keep coming up with the new ones.

    A ridiculous cap-and-trade wealth distribution scheme that would cripple the world economy, when mentioned by Obama last year, made many in Congress laugh.

    I think now that we have a reasonable balance back in the federal government, a lot of us feel much safer.

    I guess you can continue to call me a denier. I like the label.

  7. Andrew says:

    Well Shawn, you’re exactly right: the Earth balances itself out. Which is why temperatures are rising. Like Lynne, you’re asking me to get ahead of myself; this is my next post. But what you have to understand is that the Earth is in an energy equilibrium. As the amount of sunlight the Earth absorbs rises, it must emit more heat. Thus, the temperature rises. It’s happened plenty of times before in the Earth’s history. The big question is not whether temperatures will rise, but by how much. To argue otherwise is to ignore decades of research by thousands of scientists. It’d be a bit like trying to argue that the sun revolves around the Earth. But you’re obviously free to do so.

    More carbon dioxide isn’t actually a good thing for plants in the long run, or at least the ones we depend on. Yes, more carbon dioxide means more plants. But higher temperatures are not good for a lot of plants, including most of our crops. For example, in the extreme heat wave in 2003 in Europe, there was a 30% decrease in crop yields. Such temperatures will be average by the end of the century.

    I think water rising will be a larger problem than you say, simply because of the populations involved. Easily 100 million people would be displaced by a 10 meter rise in sea level (think Bangladesh, never mind Calcutta or Shanghai). In all, oceans are expected to rise by over 60 meters. Lowell sits at 31 meters above current sea level.

    The reason we’re not all dead from cancer is that the nations of the world signed the Montreal Protocol, which banned the use of CFCs and HCFCs, compounds that react with atmospheric ozone, destroying the ozone layer. It was a remarkable triumph of science informing public policy. The ozone layer has since begun to recover.

    Global cooling was a media myth that never had any traction in the scientific community. The fact that it is still repeated as a cautionary tale about science speaks more to the incompetence of our media than anything else. Scientists began warning about global warming in the 1950s; if you look for them, you can find the newspaper headlines.

    The rain forests are being destroyed…I’m not quite sure what you’re point is. There has been a massive amount of deforestation over the past few decades. And yes, we are losing thousands of species per year. The extinction rate is currently 300 times higher than is natural. 50 million years from now this will look like the 6th mass extinction event in Earth’s history. Also not sure what your point was with that one.

    As for the baby seals, I’m not going to get into that. I think the conservation movement doesn’t really understand the magnitude of the problem and has been focusing on the wrong issues. That being said, seals are being hunted pretty extensively.

    I’m not really sure what profits you’re talking about. You would think if the environmentalists had made a profit off of ending acid rain they might have had enough money to get a climate bill through Congress. Or something. What profits? Where?

    I find it interesting that you think cap-and-trade would cripple the world economy. They teach that in introductory microeconomics as the appropriate solution to the externality of pollution. I’ll come back to this one in later posts. In the meantime, you might be interested in Greg Mankiw’s “Principles of Economics.” He’s one of the more prominent conservative economists in the country and his textbook does a nice job dealing with the issue.

    And no, Congress didn’t laugh. Congress fought hard. Perhaps you should read the book I reviewed a week or so ago about the fight over cap and trade. It was as complicated and bitter as they come.

    I will continue to write blog posts. And Shawn, if you refuse to accept the evidence, that’s you’re right. But the rest of us will continue to categorize you with the flat Earthers and geocentrists. Your arguments have about the same level of support as their’s.