Monday, February 4, 2013

New paper finds natural variability controls CO2 levels, not man

An important new paper published today in Global Biogeochemical Cycles finds that "In contrast to recent claims, trends in the airborne fraction of anthropogenic carbon [dioxide] cannot be detected when accounting for the decadal-scale influence of explosive volcanism and related uncertainties." In other words, after accounting for the large effect of volcanic eruptions,  ENSO, and other uncertainties upon natural CO2 sinks, trends in the man-made fraction of atmospheric CO2 "cannot be detected." Thus, despite an exponential increase in man-made CO2 emissions, there is no statistically significant trend in the man-made fraction of CO2 in the atmosphere. This further suggests that man is not the primary cause of the increase of CO2 in the atmosphere, that temperature is responsible for the increase in CO2 levels due to out-gassing. According to the authors, "Our results highlight the importance of considering the role of natural variability in the carbon cycle for interpretation of observations and for data-model intercomparison."

Note man-made emissions are only about 4% of the total CO2 emissions in the atmosphere, and CO2 only represents about 0.04% of the entire atmosphere.


Atmospheric CO2 response to volcanic eruptions: the role of ENSO, season, and variability
Thomas Lukas Frölicher et al




Abstract: Tropical explosive volcanism is one of the most important natural factors that significantly impact the climate system and the carbon cycle on annual to multi-decadal time scales. The three largest explosive eruptions in the last 50 years - Agung, El Chichón, and Pinatubo - occurred in spring/summer in conjunction with El Niño events and left distinct negative signals in the observational temperature and CO2 records. However, confounding factors such as seasonal variability and El Niño-Southern Oscillation (ENSO) may obscure the forcing-response relationship. We determine for the first time the extent to which initial conditions, i.e. season and phase of the ENSO, and internal variability influence the coupled climate and carbon cycle response to volcanic forcing and how this affects estimates of the terrestrial and oceanic carbon sinks. Ensemble simulations with the Earth System Model CSM1.4-carbon predict that the atmospheric CO2 response is ~60% larger when a volcanic eruption occurs during El Niño and in winter than during La Niña conditions. Our simulations suggest that the Pinatubo eruption contributed 11 ± 6% to the 25 Pg terrestrial carbon sink inferred over the decade 1990-1999 and -2 ± 1% to the 22 Pg oceanic carbon sink. In contrast to recent claims, trends in the airborne fraction of anthropogenic carbon cannot be detected when accounting for the decadal-scale influence of explosive volcanism and related uncertainties. Our results highlight the importance of considering the role of natural variability in the carbon cycle for interpretation of observations and for data-model intercomparison.

7 comments:

  1. If the level of solar activity skews ENSO in favour of El Nino or La Nina over a 1000 year cycle such as MWP to LIA to date (as I contend it does) we have a good explanation for current atmospheric CO2 increases, namely ocean outgassing from a mnore active solar period.

    The quiet solar cycle 24 should soon give us an opportunity to make some meaningful comparisons regarding the atmospheric CO2 response to solar variability but there seems to be a lag period of 10 to 15 years due to the thermal inertia of the oceans.

    Stephen Wilde.

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  2. I think you have misinterpreted what is said in:
    "trends in the airborne fraction of anthropogenic carbon cannot be detected when accounting for the decadal-scale influence of explosive volcanism and related uncertainties."

    The right interpretation - in my opinion - is that the researchers have found that the airborne fraction remained constant over time, if you take into account the natural variability. That means that in average a near constant percentage of the human emissions (as mass) builds up in the atmosphere. That is either about 45% (if you take into account land use change) or about 55% (without that).

    Thus while human emissions increased over time, the buildup in the atmosphere alomst perfectly followed at a near constant ratio. Something I don't think any natural process can and will do...

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  3. Sorry, but you are misinterpretating the "airborne fraction" point: there were rumors that the airborne fraction of human emissions was increasing, because the natural sinks (oceans, vegetation) were saturating. This study simply concludes that there is no trend in airborne fraction, but that the fraction is modulated by natural causes like volcanic eruptions and ENSO events.

    With no trend in the airborne fraction, the increasing human emissions cause increasing sinks but also an increasing amount of CO2 which resides in the atmosphere. If you look in detail at the text: the researchers talk about natural sink capacity, not source capacity...

    Further, be aware that the airborne fraction is about quantities, not the origin of the molecules. It doesn't matter that human emissions may be (or not) captured within a minute by the next nearby tree, as that replaces a natural CO2 molecule that should have been captured instead.
    Every year some 20% of all CO2 in the atmosphere is exchanged with CO2 from other reservoirs, but that is exchange or turnover and doesn't change the amounts in the atmosphere, as long as the ins and outs are equal. Currently, natural sinks capture about 4 GtC more than natural sources emit as CO2...

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    Replies
    1. If the anthropogenic emissions are increasing exponentially and the anthropogenic atmospheric fraction is not increasing, then man cannot be the sole or primary cause of increased CO2.

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    2. MS, the human emissions indeed are increasing slightly exponentially, except during economical crisis, but even the current one shows an increase in emissions over the past year (mainly thanks to China...). If the aiborne fraction remains constant, then a fixed percentage of the emissions (as mass) remains in the atmosphere. A fixed percentage of an exponential function again is an exponential function. In this case both the increase in the atmosphere as the accumulated sinks increase slightly exponentially. See:
      http://www.ferdinand-engelbeen.be/klimaat/klim_img/temp_co2_acc.jpg

      You should be right if the increase in the atmosphere was larger than the human emissions, but the increase is smaller (some 45% if you take into account the uncertain estimates of land use changes, 55% from fossil fuel use only).

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  4. http://s1136.beta.photobucket.com/user/Bartemis/media/CO2GISS.jpg.html?sort=3&o=10

    Bart says:
    February 10, 2013 at 2:40 am

    http://wattsupwiththat.com/2013/02/06/the-r-w-wood-experiment/#comment-1221472

    LOTI refers to the GISTEMP LOTI global mean temperature metric at the WoodForTrees site. It is observed that it is affinely related by those parameters to the derivative of CO2 to a high degree of fidelity. Thus, to get CO2, we initialize at the beginning value in the record, and integrate the affinely mapped temperature relationship from there. The integration was done numerically with a simple rectangular formula (Euler integration).

    As you can see, the relationship is pretty darned good, and that was with no optimization for selecting the affine parameters, just pure eyeballing.

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  5. http://www.woodfortrees.org/plot/esrl-co2/from:1958/scale:0.01/trend/plot/hadcrut3vgl/from:1958/trend

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