If anyone is perpetrating a climate “hoax,” it’s the Deniers. For why, read on.
Countering one of the deniers’ favorite trick questions.
It’s not necessarily a “trick” question in all cases. Maybe sometimes it’s an “honest” error, if being honest entails burying one’s head in the sand. But in case of willful tricksters, it’s another one of those niggling questions with which they like to trip up the unsuspecting. Another piece of their hoax to confuse us.
Here’s how the question goes: A carbon dioxide molecule stays in the atmosphere for only five years. So what’s all this doom and gloom forecasting that CO2 will hang around for hundreds of years in the air even if we stop fossil fuel burning?
Yes it’s doom and gloom. But it’s based on facts (the inconvenient kind).
For an explanation, we have the carbon cycle to thank.
If you’d like a quick summation of how the carbon cycle maintains CO2 in the atmosphere—along with a nifty graphic and mind-numbing statistics—you can go to Skeptical Science (it’s ironic, meaning skeptical about global warming skepticism) and skip my long-winded treatment below. There are plenty of other links in Skeptical Science that lead you to the intricacies belying Deniers’ oversimplifications. See: Skeptical Science on carbon cycle
The advantages of my verbose treatment are that it’s more down-to-earth, goes into the chemistry and feedback effects in more detail, provides links to more in-depth stuff, and some passages may even be entertaining.
The carbon cycle is both simple and complicated.
First the simple version (the arithmetic)
Carbon dioxide molecules are extremely stable chemically, and long-lived. When they leave the atmosphere, they do not die but are taken up by oceans and plants (see below) and return to the atmosphere later. (In the very long run , they are slowly removed by rock weathering, but that’s an extremely slow process.) Any individual CO2 molecule may stay in the atmosphere on average for three to five years, but the aggregate balance of CO2 is what keeps the atmospheric load up. Think of customers going in and out of a big-box store (CO2 molecules coming and going), where the number inside the store (atmosphere) remains relatively constant, whereas any individual’s stay in the store is, say, an average of 20 minutes (analogous to the average 5-year stay of individual carbon molecule in the atmosphere). If more customers are drawn in (more CO2 emissions), the average stay of any individual customer may remain 20 minutes, but you have more customers (CO2 molecules) inside.
Over the last 800,000 years, before the addition of CO2 generated by fossil fuel burning, concentrations of the gas fluctuated around a mean of around 240 parts per million (ppm)—with a maximum of 300 ppm and a minimum of 170 ppm. For a graphical representation and discussion of the fluctuations over time, see in this page of the Climate Central website: variation of CO2 levels over 800 millennia
Now, the levels of CO2 exceed 400 ppm (note how the concentrations skyrocket in the last 100 years). That’s higher than it has been for the existence of homo sapiens on Earth.
The Climate Central graph derives from a graph on the NOAA climate site, but as of December 30, 2018, that graph cannot be reached because of a government shutdown. When the site comes back up, you should be able to find it here.
Scroll down on that same page on NOAA to find, besides graphs of the increases from 1970 to the present, the proportions between the different human-generated greenhouse gases (CO2, methane, etc.).
Note there is an error on the Climate Central page, where it speaks of a single CO2 molecule staying in the atmosphere for hundreds of years. This is misleading; while it’s possible for a single molecule to stay aloft that long, that’s the exception.
So much for the simple version. When we get to the actual physics and chemistry of global warming, we’re in for some head-scratchers.
The complicated version, Part 1: removal of CO2 from the atmosphere
For starters: CO2 is a very stable molecule. It doesn’t burn, which is why it’s used in fire extinguishers. There are few ways to get rid of CO2 chemically, since oxygen bonds to carbon as tightly as mating pythons (watch here.) The most widely practiced chemical route is plants using CO2 as an input for mass production of oxygen and glucose. Green plants take CO2 out of the air, and water out of the ground† and use energy from the Sun to uncouple and recouple their molecules to produce free oxygen and sugar (glucose; not to be confused with table sugar or high fructose corn syrup). Most of the oxygen goes back out into the air as free O2, and some gets combined with hydrogen and carbon in the glucose molecules. A tree uses the glucose (C6H12OO6), for both energy and building material. In a tree, the latter is principally cellulose, which is made up of chains of bundles of glucose. The energy from the sun gets stored in the carbon molecules That’s photosynthesis in a nutshell.
(CO2 molecule approaching a tree: “Oh no no no-o-o-o-o —” [slurp])
For the chemical structure of glucose and related molecules see:
structure of glucose et al
It’s the harvesting of sunlight along with chemical wizardry by plants that’s key to pulling apart carbon and oxygen and putting them together in new ways. We humans have yet to find a technique to pull off this feat at meaningful scale—but not for lack of trying. Since photosynthesis is relatively inefficient, there exists research to find a technology to get more with less. For one example, see: High performance artificial trees for CO2 removal
Another way to remove CO2 from the atmosphere chemically is weathering of rock by carbonic acid. This natural process is as slow as it sounds. Despite its slowness, the upside is that it removes the CO2 for a darned long time. See this in Skeptical Science: Weathering as a carbon sink
The absorption of CO2 by the oceans—not a chemical reaction, because the CO2 molecules remain unchanged—is a big deal. The oceans have sucked up roughly 40 percent of anthropogenic CO2 emissions since the beginning of the industrial era. Not only have the oceans already been absorbing a lot of CO2, the absorption continues. There’s scientific disagreement about whether the rate of absorption is slightly speeding up, or slowing, and at what point the oceans will finally have had their fill of CO2, but the bottom line is, the absorption is not keeping up with fossil fuel burning. For more detail on this part of the carbon cycle, check out this from the Swedish National Centre for Climate Change Adaptation, and/or this from the Science Journal for Kids (no offense; most of us are still kids when it comes to climate science).
Photosynthesis and oceans pull humongous bunches of CO2 out of the atmosphere. It’s partly responsible for why an individual CO2 molecule on average stays aloft for only five years. But how does CO2 get back out into the air?
The complicated version, Part 2: returning CO2 to the atmosphere
OCEANS first: CO2 escapes from oceans by desorption at the surface. Absorption in, desorption out. Once absorbed, the CO2 molecules bounce around in the oceans for years, and some bounce back out into the atmosphere: desorption. Until recently, oceans have prevented CO2 levels from soaring to 500+ ppm during the last 100 years, while humans burn carbon ever more furiously. That’s relatively good news (for us, not for marine organisms)—oceans acting as “carbon sinks.” But the bad news is that in warmer water the dissolved gas molecules bounce around ever more enthusiastically and escape from the surface at a faster rate. Once back in the air, CO2 returns to trapping heat. This is another feedback mechanism that drives the acceleration of global warming.
CO2 molecules leaving the ocean more swiftly compounds the problem of accelerating evaporation of water into a warming atmosphere. Since water vapor is the most abundant greenhouse gas, this phenomenon traps even more heat. And then—you get the idea, it’s another instance of “positive” feedback.
Warming oceans are a triple threat: releasing CO2 at a faster rate, releasing water vapor at a faster rate, and expanding to produce rising sea levels.
However—this is where it gets really complicated—the escape of CO2 from oceans into the atmosphere might be counterbalanced by a recently discovered circulation phenomenon that could actually be speeding up oceanic absorption of CO2 in coastal waters, at least temporarily. For this piece of counterintuitive news, see Absorption of CO2 in coastal waters.
Moreover—complication upon complication—clouds resulting from condensation of water vapor reflect solar radiation back into outer space, which has a cooling effect (that’s an oversimplification—most but not all clouds have a net cooling effect; high thin clouds produce the opposite). For more on water vapor, check out this from NOAA: Water vapor and the Greenhouse Effect
Clouds are the joker in the climate change deck, as you may have surmised by reading that last reference from NOAA. Clouds don’t fit easily into climate models because of variety, transience, and difficulty of measurement. Nevertheless, the overall impact of clouds is cooling—by how much is unknown.
Earth is finding ways to cool itself off even while we’re loading it up with greenhouse gases. Unfortunately, at this point carbon burning is gaining in the game of checks and balances that is Anthropogenic Global Warming .
If you’ve had enough of oceans, sorptions, water vapor, and clouds (I have), let’s turn to the simpler role of plants in the carbon cycle.
===========On to Plants==============
PLANTS: Eventually, most carbon taken in by plants as carbon dioxide returns to the atmosphere via oxidation. Oxidation combines the oxygen in the atmosphere with carbon stored in the plant to yield CO2.** Oxidation can be as fast and showy as fire, as common and mundane as respiration in animals, as slow and humble as rot. But at any pace, it is as reliable as sunrise. Inevitably, all plants die, followed by oxidation fast or slow—the phase of the carbon cycle where the sun’s energy that got bound up during photosynthesis is released. Planting more trees—which tie up large amounts of carbon for a long time—might help us get CO2 out of the air long enough to avoid a near-term climate crisis. But we are talking about a lot of trees. What with the pace of deforestation today, you have to plant a lot of trees in a hurry just to make up for the massive amounts of trees we are now killing, long before we get to a carbon-neutral, much less a carbon-negative stage. Boreal forests are expanding northward with warming of the climate, which is helpful, but boreal trees are chumps at removing CO2, because of long winters and low sun angles even in summer.
Is char the answer? Plants can’t get us to carbon neutrality, UNLESS you have a way of cooking carbon under low heat, such that most of the carbon, instead of being oxidized, stays in heaps of “biochar.” It’s like charcoal, but broken down to be easily mixed into soil, thus sequestering the carbon for hundreds to thousands of years. Proponents claim that this is not just carbon neutral, it is carbon negative—pulling more carbon out of the atmosphere than it releases. See: Reversing climate change with charcoal?
But hold on! Char is not what it cracks up to be, says Dr. Mae-Wan Ho on the Permaculture Research Institute website. For starters, char locks up not just CO2, but also oxygen, and atmospheric oxygen is on the decline. Secondly, burning anything that contains carbon is playing with—er—fire. Before you read Mae-Wan Ho, be aware that the core of his long argument is that oxygen decline poses a serious threat, about which there is keen skepticism among scientists: The dark side of char.
Hoaxification of volcanic CO2
Before wrapping up this segment, we need to take into account another of those tangential phenomena that Deniers pounce upon, in order to undermine the argument that human activities are largely to blame for soaring atmospheric CO2 levels. That’s the claim that volcanoes release more CO2 than human activities. That idea was promoted by geologist Ian Plimer in his 2009 book, “Heaven and Earth: Global Warming — the Missing Science.” The main problem with Plimer’s volcano claim is that the “Missing Science” of which he speaks is exactly that—missing. In fact, human-emitted carbon dioxide levels are at least 130 times higher than volcanic emissions. For a takedown of Plimer’s contribution to the Hoax of Denial, see: Terry Gerlach blows up Ian Plimer
Implications for climate skepticism/denial
This is a long way around to countering the climate change denier’s tricks. But the complexities touched on above go to the heart of the contentiousness between climate scientists (joined by most other scientists) and deniers.
Few climate change deniers are the “skeptics” they style themselves as. True skeptics go deeply and broadly enough into a phenomenon to come up with a thesis, where many parts are integrated into a whole—not cherry-picking this or that factoid favorable to the “skeptic’s” case. As evidence of Anthropogenic Global Warming piles up, true skeptics are becoming harder to find.
In the case of climate science, to research the phenomenon is to plunge into not just one, but many interacting features of Anthropogenic Global Warming. It takes multiple contributions between scientists and teams of scientists to figure all this out. Yes, they have disputes about different aspects of the problem, such as how much CO2 the oceans are likely to absorb, but those take place within overwhelming agreement that the planet is warming quickly, it’s dangerous, and people are causing most of it.
What I’ve discussed above only scratches the surface of the climate conundrum: not all is as it seems. Can the oceans continue their work as carbon sinks? Is there a saturation point—if so, when? How much do certain types of clouds reflect solar radiation? How much do certain other types of clouds retain heat? How big a part do boreal forests play in the carbon cycle? Is biochar the magic bullet to sequester carbon?
Even the smartest scientists lack complete answers to all these questions. Climate science is probabilistic: the more evidence comes in, the more hypotheses are proposed and tested, the more models are refined, the more certain the science becomes. But there’s never the level of certainty as in, you drop two rocks of different weights from a tower, they hit the ground together. That’s the kind of certainty non-scientists crave, but it’s not to be had in many branches of science. Therefore, there’s always a gap in understanding for a denier or pseudo-skeptic to try to pry open. But as time goes on, the gaps in climate science are getting smaller, and the fit between the many parts is getting ever tighter. Tightening enough to crush the skulls of many a denier venturing therein.
FINAL NOTE: I have focused on CO2 in this post, ignoring its evil sibling, CH4: methane. The rise in methane emissions is cause for alarm, since methane is a greenhouse gas many more times as powerful as CO2 (on approx. a 12-year basis; it does not persist nearly as long in the atmosphere). Subject for a later post.
================FOOTNOTES====================
* And carbon in us and other animals, of course. Carbon is by mass the second most abundant element in the human body (16 kilograms in a 70 kg human) behind only oxygen (43 kg). Most of the oxygen is present in water, since there’s 38-42 kg of water in a 70 kg person, leaving carbon to handle structural tasks. Uranium, by the way, is well down the list at 0.1 milligrams.) See Table of elements in human, by weight
** The concentration fluctuates seasonally, largely on account of plant growth. In the Northern Hemisphere, it dips from June through September and climbs up again from October into May (see from Scripps Institution of Oceanography.
Moreover, El Nino warming may push CO2 levels up for years at a time. (See in Al Jazeera here.) El Nino events have a lasting effect: feedback dynamics force more warming even when the El Nino subsides.
*** The oxidation of carbon in a plant releases the energy it took from the Sun to perform photosynthesis. Much of this energy is released as heat, to heat your home, propel your car, and make it cozy when roasting chestnuts over an open fire. Heat is used directly in many industrial processes such as smelting metals. In a thermal power plant, such as coal-fired and natural gas-fired stations, the heat converts water into steam which drives the turbines to generate electricity. Since coal and oil result from compression of humongous amounts of plant material over millions of years in the past, they release huge amounts of energy per unit of weight. (Nothing compared with radioactive elements, however; uranium 235 produces three million more times as much energy per unit of weight, with no carbon emissions.)
† A few plants such as epiphytes (e.g. orchids) get all or most of their water from the air.