Emissions and Concentrations–How Closely Are They Correlated?

Update: I asked climate scientist Bart Verheggen if he could shed some light on this issue–He did down below in the comments. His explanation makes perfect sense. If I can paraphrase Bart, even if emissions decrease, if the total emissions exceed the rate at which the natural sinks can remove our contributions, concentrations will increase–but see below for his full explanation. Thanks, Bart!

Over at my companion blog I posted on some surprising hiccups in the relationship between CO2 emissions and CO2 concentrations. After commenter pottereaton called my attention to an article Alexander Cockburn wrote, (where he noted that emissions declined but concentrations rose during the great depression), I took a quick look and noticed that the same thing happened in the early ’80s.

CO2_Emissions_vs_Concentration

Of course it’s only in a fantasy world that they would move in lockstep, but it’s certainly curious that concentrations would rise 4 years in a row when emissions fell each of those four years. Well, here’s a look:

Base year 1979. Emissions in millions of metric tons of carbon (to convert to CO2, multiply by 3.667). Concentrations are in parts per million (volume). Emissions come from CDIAC. Concentrations come from NOAA.

Emissions Concentrations
1979 5,369 336.78
1980 5,315 338.68
1981 5,152 340.10
1982 5,113 341.44
1983 5,094 343.03

The total fall in emissions is small–275 million metric tons in total. But the rise in concentrations is significant–6.25 ppm. The four previous years showed a rise of only 4.73 ppm, despite emissions increasing 505 metric tons. The four subsequent years were very much the same–concentrations increased 4.36 ppm while emissions increased 513 million metric tons.

In fact, in 9 years since 1959, emissions have decreased. In every one of those years, concentrations increased. The years that Alexander Cockburn looked at were 1929-1932. Emissions fell by 30%–but concentrations rose (slightly), from 306 to 307 ppm.

Look–I can understand that the response from our climate lags behind the things we do to it (and we do a lot…). But four years of declining emissions should have some sort of an effect on concentrations, shouldn’t it?

That is, if human emissions of CO2 are the driving force behind increased concentrations….

Last year I noted that one-third of all human emissions had occurred since the current (or perhaps recently expired) pause in temperature rises. I said then that it made at least a partial argument against high sensitivity to emissions. Looking at this I begin to wonder just how much of an effect our emissions are actually having.

I’d love a scientist to come and explain this to me. By which I don’t mean being patted on the head and told that natural variability explains it all. If it is natural variability then where else do we see it, and where do we see it going in the opposite direction? Where are the cases where concentrations fall for a couple of years despite increasing emissions?

12 responses to “Emissions and Concentrations–How Closely Are They Correlated?

  1. I would love to hear that explained also, Tom.

    I would also love to hear how we can assume that a temperature reading taken on, say, a street in London in 1890, can be compared in any meaningful way with the same reading at the same location with all other things being equal, on the same street at the same location in 2015. And assuming that it is understood that conditions are not the same, how do they adjust for the man made differences that might be effecting the thermometer readings at that precise location?

    Localized human impacts on temperature must be huge. In 1890, there were no cars in London. In 2015, there were, I would guess, hundreds of thousands. I just wonder how scientific it is to be making the claim that temperature comparisons over long time spans are accurate because conditions, measuring equipment, and a variety of other factors are in constant flux. Science and its methods are as nearly subject to change as . . . well, as the weather.

    The idea that we can assume conclusively that temperatures are a little bit higher today than they were 125 years ago, is delusional. How do you make all conditions equal in an effort to make that comparison? Adjustments? How do we know they are accurate when we are, after all, dealing in tenths of degrees?

  2. Tom, I’m glad you discovered Cockburn. He published the article that got me on Greenpeace’s blacklist. Some of his old buddies blog for Aletho.

    The standard argument to explain increasing concentrations when emmissions decline is that co2 concentrations follow temperature increases not vice versa. The oceans ability to hold co2 decreases as it warms up.
    You also have to consider the role of things like deforestation which eliminate co2 sinks.

  3. Hi Tom,

    The concentration is an integral measure: Concentration increases when emissions exceed removal, and it decreases when emissions are lower than removal rates. Over timescales of a few years, emission rates are approx double the removal rate, i.e. about half of what we emit stays in the air, the other half is taken up by the oceans and the biosphere.

    Thus, if during a certain period emissions decrease, but remain higher than the removal rate over that same period, the concentration will still increase. Nothing strange about that, though it appears counterintuitive at first.

    The reverse (emissions increasing and concentration decreasing) is much less likely, because that would imply that the removal rate would be more than quadrupled suddenly, which is not very likely.

    An interesting paper linking these sorts of issues to common stock-flow problems is this one: http://scripts.mit.edu/~jsterman/docs/Sterman-2007-UnderstandingPublicComplacency.pdf The problem sets in Figure 1 are very enlightening in this respect I find. I use them in my teaching.

    Another relevant source re recent CO2 emissions and concentrations is https://www.wmo.int/pages/mediacentre/press_releases/pr_1002_en.html

    The CO2 removal rate is highly variable, and depends a.o. on e.g. ENSO and volcanism (see e.g. https://klimaatverandering.files.wordpress.com/2014/04/gw_toekomstige_co2-concentraties_3.png). This is part of a Dutch guestblog by carbon cycle scientist Guido van der Werf https://klimaatverandering.wordpress.com/2014/04/16/toekomstige-co2-concentraties/ (google translate may help making sense of it).

    • Hi Bart,

      Thanks for coming over and straightening me out. Your explanation makes sense to me, at least. I do appreciate it.

    • Hi again, Bart… as long as I’m in basic learning mode, can you answer another question?

      What I always read is that the carbon sinks of the world absorb about half of our emissions of CO2. Seems natural, logical.

      What I don’t get is why the sinks can absorb 4 million metric tons of carbon when it is half of an annual emission of 8 million tons (as in 2005), but fail to absorb the same 4 million tons when it is 100% of the total (as in 1970).

      Can you explain a bit for me?

      • Something like there is more to be absorbed, so it gets absorbed more.
        Like how water empties faster from a tub if it is filled to the top.

  4. As China, India, and others increase their CO2 emissions, the feasibility of the 80-90% reduction in emissions as called for by climate models will make action impossible. Then I suspect the science will be adjusted so as to make a freeze of emissions the new goal.Beenstock and Reingewertz will become the new paradigm.

  5. “it’s certainly curious that concentrations would rise 4 years in a row when emissions fell each of those four years”

    It is not really curious. The red graph is the total amount of stuff, the blue is the RATE at which new stuff is added.

    Imagine you are filling your bath. The water level (red curve) increases. Then you turn down your tap slightly (from level 18 billion to level 17 billion). Obviously the water level still goes up.
    In reality it’s more complicated, because there are natural sources and sinks as well.

  6. I wonder how accurately they know the “human CO2 emissions” number. This cannot be accurately measured. I suppose one can add up all power plant and car emissions, etc. I’ve seem wildly varying estimates for cow emissions.

    The same goes for CO2 removal rate. Not obvious how much error is this number.

    What we can actually measure is the delta (emissions out – emission absorbed).

  7. Having read Bart Verheggen’s response, the Sterman 2007 paper and Paul Matthew’s bathtub analogy, I’m still missing something. It seems they’ve answered an interesting question, but not really the one you asked.

    Their responses neatly lay out that total concentration must continue to rise if the emissions exceed the ability of the system to absorb them. Right – no argument or question there.

    However, they do not at all address the question of why the concentration seems to have been rising in a very constant fashion, even as the added emissions go through multi-year swings (down in 80-84, sharply up in 02-07).

    To further abuse the bathtub analogy, it’s as though we reduce (and later speed up) the overfill rate, but are finding that the water level is rising in a very linear fashion. Something else seems to be going on. What is it?

    If that something else is that (per Bart Verheggen), “the CO2 removal rate is highly variable…”, it is at least curious that the variability so neatly cancels out the input fluctuation.

    • I agree. And, even more striking is the same rate of growth of concentration, regardless of whether emissions are high or low. Take this simplified example. Suppose the rate at which CO2 “flows out of the bathtub” is 15 billons tons per year. Emissions in 1970 were a bit below 15 billion tons, so the excess emission in 1970 was slightly below zero. Over time, excess emissions grew dramatically to around 17 billion tons. You’d think the concentration would have grown much faster in recent years than in early years, but it grew at about the same rate throughout the period.

      BTW does anyone know how to relate ppm of concentrations vs. tons of emissions? One would imagine that the annual rate of growth of the concentration is approximately equal to the annual amount of excess emissions. But, since they’re measured in different units, I am unable to make that comparison. If someone knows how many tons of atmosphere the earth has, it should be possible to relate the two units.

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