Is This the Last Year Below 400?

In Home, Keeling Curve History, Measurement Notes by Rob Monroe26 Comments

Leader of Keeling Curve measurement says temporary bump from El Niño could push atmospheric CO2 levels above symbolic threshold for good

The Mauna Loa CO2 record is a saw-tooth pattern, with CO2 concentrations typically falling from May through September, and rising over the rest of the year. This cycle is caused by the natural exchanges of CO2 with vegetation and soils. Each year, the values are higher than the year before, as CO2 continues to pile up in the atmosphere from fossil fuel burning. This year, as expected, we hit the annual low point back in September and CO2 concentrations are starting up again. The lowest point this year was well below 400 parts per million (ppm). The lowest daily minimum this year was 395.83 ppm and the average for the month of September, was around 397.1 ppm. By sometime in the next month or two, CO2 will again rise above 400 ppm. Will daily values at Mauna Loa ever fall below 400 ppm again in our lifetimes? I’m prepared to project that they won’t, making the current values the last time the Mauna Loa record will produce numbers in the 300s.

The background for my forecast:

In recent years, CO2 has been increasing by around 2.2 ppm, per year. Barring anything unusual, we would therefore expect next year’s September value to be around 399.3 ppm, just barely below 400 ppm, and we’d expect the lowest daily minima to be around 398 ppm or so. But we seem now to be on the verge of the largest El Niño event since 1997. This is significant because CO2 tends to rise much faster during and just following El Niño events. From September 1997 to September 1998, for example, CO2 rose by a whopping 3.7 ppm. If this El Niño is comparable, the rise from September 2015 to September 2016 could easily be 4.4 ppm, allowing for an El Niño boost and allowing that fossil-fuel emissions rates globally are larger now than in 1998. Taking these factors into account, a reasonable forecast for next year’s September minimum is around 402 ppm, with the lowest daily minima also over 400 ppm.

The El Niño growth spurt in atmospheric CO2 is mostly caused by drought in the tropics. Rainfall that normally falls over tropical landmasses shifts to the oceans during El Niño events. This slows the normal growth of tropical forests and increases forest fires. Indonesia suffered severe fires during the 1997 event and, from recent news, is already being hit hard this year.

The loss of carbon from tropical forests in El Niño years is temporary as the forests tend to regrow in normal years, building back their biomass and sucking CO2 out of the air in the process. But the eventual recovery from this El Niño won’t bring us back below 400 ppm, because its impact will be dwarfed by the global consumption of fossil fuels, pushing CO2 levels ever higher.

­ – Ralph Keeling


  1. Dave Cline

    Do La Nina events generally have the opposite affect on the CO2 adsorption patterns?

    Will the ocean be reaching a saturation point anytime soon? If so, when? And if so, wouldn’t this also have a considerable boost affect on atmospheric CO2 levels?

    At what point do CO2 levels have an obvious and helpful affect on the expanded growth rate of plant life? Are we already seeing evidence of more robust growth due to the 400ppm levels today? I realize that such increases in growth rates most likely pale in comparison to the Stairway-to-CO2-Heaven of the last 50 years, but knowing the impact would still be useful.

    1. Gregg

      Something that I thought was missing here was the fact that 47 million acres are deforested each year (1.5 acres per second). With that in mind, there are fewer acres of forest now than there were in 1998 and the buffering caused back in 1998 is huge compared to what we are likely to see in 2016.

      1. Vonn


        I would have to agree with your statement. The other positive feedback loops that are taking place all over the globe are not being factored into this projection. The only factor being calculated is carbon emissions by fossil fuel consumption. This does allow the researcher to make a cautious prediction, but we are way past caution now. We need governments and leaders to wake up!!

      2. Jeff Lewis

        1.5-acres lost every second translates to a forest 4.6 times the land area of Texas, all removed since 1998.

        Big Farms and residential use of herbicides are also likely not helping. We are systematically destroying the carbon-absorbing capacity of most of the land surface, at least in the so-called advanced economies.

        1. Dave Cline

          I’ve read of recent comparative satellite imagery of Russian’s tiaga forests, pitting 1960 photo graphs with current images, and noting that there has been measurable increases in forest growth since then. That part of the planet seems to be welcoming the increase in CO2.

          Additionally recent North Atlantic studies of coccolithophores showing a spike in population growth, perhaps attributable to increase in CO2.

          1. Jeff Lewis

            That “2-20%” ‘spike’ in coccolithophore populations in the North Atlantic pales next to the spike in World Population of Homo sapiens (3.3B in 1965, grew to 7.3B today).

            Even worse, our appetite for consuming fossil fuels appears to be far out of balance. Nature tries, but she cannot keep up with our pace for hyper-consumption.

  2. Kevin Hester

    Ralph Keeling has forgotten more about climate change than I know but I question whether the drought stressed forests will ever recover.
    “The loss of carbon from tropical forests in El Niño years is temporary as the forests tend to regrow in normal years, building back their biomass and sucking CO2 out of the air in the process.” I believe Gail Zawacki from the Whitsend blog would debate whether these forests will ever recover.
    Bill McKibben and the Rockerfeller Foundation funded are going to need to review the name of their organisation now that it is official from the sage on Mauna Loa that 400ppm of CO2 is gone and never to be seen again as Guy McPherson has long predicted.
    Brace for impact.

    1. Gail Zawacki

      There is more than El Niño at work. Forests are dying off all over the world from absorbing air pollution. The background level of ozone is appx 40 ppb, with higher concentrations on top of that. Damage to trees that absorb ozone is cumulative, and we have passed a tipping point where they can no longer tolerate this toxic gas. They are weakened and succumb to opportunistic epidemics of insects, diseases and fungus. Their roots shrink in response to the damage and they become more vulnerable to drought and windthrow. It’s not surprising that there are more landslides and wildfires. It’s going to get a lot worse – and CO2 is going to spike as we lose a critical sink.

        1. robertscribbler

          Hello Kevin. A good rain will mostly put these fires out. The problem is that some of the Indonesian fires are burning through peat. And peat fires can just burn and burn and burn. The other issue is that human forced warming generates a preference for drought in the equatorial regions. One wonders if these forests in Indonesia and the Amazon can ever fully recover from these compounded climate insults, especially when human beings are also actively clear cutting and burning them.

  3. Tom Simon

    Can someone give me an idea of what 400ppm means in relation to atmospheric weight? An example I saw from 2007 at 383 ppm the total weight of CO2 = 0.0582% x 5.1480 x 1015 tonnes = 2.996×1012 tonnes

    What effects does this continued build up of weight have ? Chicken Little does come to mind.

    1. Karen Stelly

      Tom, I don’t believe there is a significant enough increase in the weight to do much, or even be noticeable to us humans. Since air pressure fluctuates all over the planet due to weather conditions, and whether the air is rising or falling, this extra weight would be negligible. If we go with the basic premise of percents and standard air pressure at sea level of 14.7 pounds per square inch , we can estimate the CO2 fraction of the air is 0.006 pounds per square inch (very rough estimate). The 14.7 pounds per square inch equates to 1013.25 mb. At present time, Hurricane Patricia has broken the low at 879 mb. The tiny weight increase will not be noticed. If it is noticed, it will mean higher pressure, which in turn means rising air, and drought in the long term. But of course, the dynamics of the atmosphere are much more complex because of the constant change on a daily basis.

  4. Karen Stelly

    Amen! I have been telling my students for a few months now that I predict 2016 will have an annual average over 400 ppm. The numbers speak for themselves.

  5. William Fraser

    I’m pretty sure that we have just crossed the 400 point in terms of the 12 month rolling average.

    Can anyone pinpoint the date it happened more exactly?

    1. Dave Cline

      Using the raw monthly data:

      You might be right. They have not added Sept to the data set yet. But yeah, by now I’d expect it to be over 400. Here’s the last rolling 12 months:

      2014.7068 395.41 398.0816667
      2014.7890 395.65 398.2516667
      2014.8740 397.22 398.4283333
      2014.9562 398.79 398.6
      2015.0411 399.86 398.7691667
      2015.1260 400.31 398.9608333
      2015.2027 401.52 399.1316667
      2015.2877 403.43 399.3066667
      2015.3699 403.70 399.4583333
      2015.4548 402.45 399.5541667
      2015.5370 401.13 399.7241667
      2015.6219 398.60 399.8391667

      1. Karen Stelly

        According to my calculations, if we include the September reading of 397.64 (, the 12 month rolling average is 400.025

      2. Karen Stelly

        With the November average of 400.16, the 11 month average for 2015 is 400.7. The December average will also be above 400, ergo, 2014 was the last year below 400 ppm.
        399.96 Jan
        403.26 April
        398.82 Aug
        400.16 Nov

  6. Brett Courtenay

    The permanent average of 400 ppm from now on, is of course, a symbolic point but an important one nonetheless, if only to remind us that the Planet has NOT had a CO2 atmospheric content this high since before our Species began.

    It is also indicative of how we have so far failed to not only address the issue, but even agree there is an Issue…if the denying attitudes of most GOP Presidential Nominees are to be heard.

    The Paris Climate Talks are about to begin…yet Humanity has hardly begun to resolve what needs to be done and even whether some key parties will agree to what those agreements might be , following the talks…

    It is critical that we employ ACTIONS…we have heard enough Talk from the Planet and our readings from this conversation are clear and obvious.

    We cannot act fast enough to mitigate the consequences of our inaction to date , let alone the reality that will only become worse from the paths we took on the roads we built these last 100 years.

    The Huge Greenland Zachariae Isstrom glacier has started to break up and is calving as reported worldwide today…do we really need any more ominous examples of what is happening to spur us on?

    The Time for Action is Yesterday. The price of failure is a broken Tomorrow for our Children and their Children.

    We must act decisively…it’s no longer about a +2 celsius or +4 celsius World.

    It is about making sure we do not create the opportunity for
    “The Great Methane Release” be it from the thawed Tundra or (God help us) The Deep Ocean…if either release the Methane held …its Game Over.

    This are the Make or Break Times..and we are already running late.

  7. Sven-Olof Hålling

    I think mother earth is soon starting up the reduction process.
    The earth is a survivor , so don´t worry be happy !

    1. Jeff Lewis

      I could not get through the pay wall, to read the actual report, but I think we all welcome negative feedback phenomena, should the emerge (after all, the trend these past few years has been quite scary, with most feedbacks being positive toward CO2 acceleration). Reading the abstract, though, the phrasing does not clearly indicate “a 10X increase”; the actual phrasing was “…we show that coccolithophore occurrence in the North Atlantic increased from ~2 to over 20% from 1965 through 2010….” My best-fit interpretation of this odd phrasing is the authors are saying that North Atlantic populations of the species has increased nominally 11% in the past 45-years … a timeframe during which a 26% increase in atmospheric CO2 occurred.

      1. Larry Shipley

        If you cough up a few bucks to read the full text, they clearly say there has been a 10 fold increase over that time.

        And to your earlier point about in the % increase in human population compared to the % increase in coccolithophores, your comparison of percentage increases is a non sequitur. You would need to compare the mass of CO2 output from the total human population to the mass of CO2 consumption by the population of coccolithophores over a given period of time. I don’t happen to know what those numbers are, but that would be the meaningful comparison.

        The biosphere is a very complicated system. Even the most learned don’t claim to fully understand it. Monitoring by the good folks at Scripps increases our understanding. And we thank them for it.

        1. Jeff Lewis

          Good… glad to hear someone has spent a few coins to read the article, and maybe clarify a poorly written (ambiguous) abstract.

          I found a much more informative article, at this link:

          The article does include the quote: “Published Thursday in the journal Science, the study details a tenfold increase in the abundance of single-cell coccolithophores between 1965 and 2010, and a particularly sharp spike since the late 1990s in the population of these pale-shelled floating phytoplankton.”

          Nature is beautiful this way, and it is nice to see what may appears to be a moderating feedback. But, is this feedback at a scale that can significantly counter for the full extent of atmospheric carbon loading as it stands today? When the platform blew in the Gulf of Mexico a few years ago, it would have been nice if they could have just pointed a garden hose at it to stop the gushing. In a worst case scenario, we may find today’s rate of fossil fuel consumption is like that blown Gulf platform: a massively scaled problem, completely out of control, no matter what Nature might do to help.

          As for Scripps, well… thanks to their steadfast support for the Keeling Curve, we have a very powerful data-weapon to fight back against the greed and deception of BigOil (and their paid servants). If the AGW cause can gain enough concern and support, we may just find ways to slow or even stop our own extinction.

  8. Yves

    One can also notice that, according to the NOAA/GMD website, the season-corrected global CO2 average crossed the 400 ppm mark this October: 400.17 vs 399.91 in September. Since the season-corrected curve is nearly monotonous (compared to the globally-averaged value which exhibits seesaw behavior), it can be expected that the 400 ppm mark won’t be crossed again before the last decades of this century.
    The values are the righthand column (titled “trend”) of this:

Leave a Comment