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A 23-year experiment finds surprising global warming impacts already underway

Posted on 9 February 2015 by dana1981

A new paper published in Global Change Biology summarizes the results of a 23-year experiment monitoring how global warming is impacting certain ecosystems.

At the Rocky Mountain Biological Laboratory, the scientists have monitored ten 30-square meter plots of meadowland since 1989. Above five of those plots, overhead infrared radiators have been on constantly since January 1991, while the other five were used as the controls for comparison. The study reports,

The microclimatic effect of experimental heating throughout the growing season has been to warm the top 15 cm of soil by ~2 °C and dry it by 10–20% (gravimetric basis) during the growing season, and to prolong the snow-free season at each end by an average of ~2 weeks.

Ecosystem Changes Amplifying Global Warming

The scientists monitored the type of vegetation growing in the meadows. In both the controlled and heated plots, they saw a shift away from flowering plants, towards woody plants like sagebrush, with a bigger change in the heated plots.

They also monitored the amount of carbon in the soil. In the heated plots, the amount of carbon stored in the soil decreased, but it later rebounded. In the control plots, the carbon storage decreased more slowly, and hasn’t yet rebounded after 23 years. Simulations suggest the soil carbon storage will continue to decline for about anther 40 years before it rebounds.

100-year simulation of soil carbon storage in mountain grasslands and meadows 100-year simulation of soil carbon storage in mountain grasslands and meadows. Photograph: Harte et al. (2015), Global Change Biology.

The change in carbon storage was caused by the shift from flowering to woody plants. As lead author John Harte of UC Berkeley explained,

When shrubs replace forbs [flowering plants], the rate of input of organic carbon to the soil declines because in these ecosystems forbs photosynthesize at a higher rate (per area) than do the shrubs and return more annual growth to the soil at the end of the growing season. The loss of all that annual production leads to a rather rapid decline in soil carbon (the quantity factor). But the soil carbon arising from dead shrub leaves is less digestible than is the soil carbon from forbs (the quality factor).

Over a period of decades, this leads to the eventual recovery of the soil carbon. The delay in the influence of the quality factor is due to the fact that until the soil carbon resulting from shrub production has built up to a sufficient level, most of the soil carbon will still be that from forbs.

The study notes that a similar change happening as spruce forests convert to pine forests. This shift results in less carbon storage in both the short- and long-term, causing what’s called a “positive feedback,” as more carbon remaining in the atmosphere will amplify global warming further. I asked Dr. Harte if he could speculate about whether these results give us an indication about how we can expect carbon storage in the global biosphere to change in a hotter world. He told me,

A basis for speculation at the global scale comes from ice core data showing that over the past hundreds of thousands of years, during periods in which earth is warming, atmospheric CO2 levels rise, and during periods in which earth is cooling, those levels drop. The oceans undoubtedly play a big role in this but it is likely that terrestrial ecosystems also factor in. While we can’t yet be quantitative, there is good reason to believe that the terrestrial contribution is on average, one of positive feedback (that is, contributing to the global trend revealed in the ice core data).

Changes Happening Sooner than Expected

While some of the changes in the heated plots were expected, the scientists were surprised that they saw similar changes occur in the control plots. Since 1991, the snow-free season has become extended, the soil has become hotter and drier, and there’s been a shift from flowering to woody vegetation. Harte said of his research,

We were actually very surprised to see such dramatic changes in the control plots. That the plant community could undergo such rapid change, from a carpet of wildflowers to sagebrush, in just a couple of decades under the artificial heaters was not a surprise. But that the same transition would be visible in the ambient plots was a surprise; we expected that such a transition would take at least 3 or 4 decades.

And even more surprising was the clear evidence after two decades that the ambient plots were losing soil carbon to the atmosphere. A number of soil scientists said that it was a waste of time to measure soil carbon because we would never detect change in the lifetime of an experiment. Not only could we detect it rather rapidly in the heated plots, but it is now apparent even in the ambient plots. 

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Comments 1 to 16:

  1. Interesting, thanks for posting.

    Makes those climate models with atmospheric carbon declines as CO2 emissions cease despite continued warming of at least 1C further, seem optimistic.

    With permafrost melting, forest fires raging, record droughts drying and climate zones shifting (replacing tundra with shrubs then pins releases soil carbon as well), a fall in CO2 just by stopping emissions due to CO2 fertilizations effects seems unrealistic. Macdougall et al found CO2 increases even if all emissions stopped in 2012 unless the CS was below 3C which seems more and more unlikely as time goes by.

    "Significant contribution to climate warming from the permafrost carbon feedback"

    Andrew H. MacDougall*, Christopher A. Avis and Andrew J.Weaver Natture GeoScience 2012

    350-400ppm = Early Pliocene we are at 460ppm CO2e.

    How much is the carbon budget?

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  2. Good points, ranyl. And it's always good to keep that MacDougall study in mind.

    But when you say: "a fall in CO2 just by stopping emissions due to CO2 fertilizations effects seems unrealistic. "

    ...while I agree, it is my (mis-?)understanding that the primary draw down of atmospheric CO2 after any hypothetical total stoppage of human emissions will be continuing absorption of the gas into the oceans, as they reach equilibrium with the atmosphere.

    Even this, as MacDougall et alia show in the article you cited, though, is not enough to expect immediate reductions in atm CO2 levels even under the essentially impossible scenario of total, immediate sessation of all further human emissions.

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  3. HI Wili,

    See article at HTML.

    There is no doubt that the oceans have been a major sink, however as temperature rises water can absorb less and less CO2,

    also as they acidify oceanic sinks can turn to sources.

    Further the oceanic desserts are growing, and dead zones increasing and biodiversity is dropping all of which will not help the future prospects of CO2 absorption.

    Further again, as the southern hemisphere warms and the winds move south they draw up more water from the depths and this water is CO2 rich and releases CO2 from the ocean's depths and warms the base of the below sea level based ice sheets.

    Therefore not sure the oceans will provide CO2 salvation.

    Not unless through our actions (or none actions (i.e. not putting toxic waste in the water)), an oceanic ecosystem and biodiversity boom can be utilized, still going to lose many coral reefs, not sure what happens to CO2 releases associated with coral die offs?

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    Moderator Response:

    [JH] Links activated. Please take the time to learn how to use the Editor's link insertion tool. Thank you.

  4. Good points. I in no way meant to imply that the oceans would
    "provide CO2 salvation." Only that they are important in understanding the short term dynamics of CO2 exchange going forward.

    Once equilibrium is reached, offgassing from the oceans will keep atmopsheric CO2 levels high for thousands of years, at least.

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    Moderator Response:

    [JH] Please provide a citation for your concluding statement. Thank you.

  5. Interesting but neither the article or its referenced source – a précis – indicate the effect of infra-red heated plots in terms of what is to be expected from global warming this century. Nor does it appear to show likely effects on food crop yields which, after all, must be the primary concern of farmers, governments and a burgeoning hungry population.

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  6. Hmm, interesting. A few thoughts occurred to me, though. (I can't see the paper itself, even if I could access it, as there seem to be some problems with the site, at the time I tried).

    This experiment, presumably, measured 23 years of a constant surface warming, above the variation already happening. But didn't/couldn't simulate a higher atmospheric concentration of CO2, over an extended time. Also, I'm not quite sure of the usefulness of measuring just the soil carbon. What about the carbon in the woody shrubs, also? That is, what was the total carbon sequestered by the plots (I realise that the soil carbon would come from the plants growing in the plots)?

    I also wonder if this result has implications for one of Hansen's hopes; that reforestation would help bring CO2 levels down.

    Lastly, presumably the shift from flowering plants to woody plants is due to those plots being in naturally woody areas, since the same occurred on the control plots. What would be the difference from natural prarie ecologies?

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  7. "We were actually very surprised to see such dramatic changes in the control plots."  It's very well known that tropospheric ozone is highly toxic to vegetation and that as background levels rise, there will be a species shift in the ecosystem because some plants are more sensitive than others.  That is what is occurring everywhere on earth.  It shouldn't be a surprise.  The reason the EPA has been (unsuccessfuly so far) trying to enact stricter legislation to lower acceptable levels of ozone is to protect the biosphere, because they have determined after reviewing the scientific literature that damage to trees is cumulative.  This is a massive amplifying feedback for climate change, as a major carbon sink is being lost, as well as other knock-off effects such as changes in precipitation and of course, habitat and food for dependent species.  See links at

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  8. I wrote: "Once equilibrium is reached, offgassing from the oceans will keep atmopsheric CO2 levels high for thousands of years, at least."

    To which the Moderator Response was:

    "[JH] Please provide a citation for your concluding statement. Thank you."

    OK, I guess you got me. I guess I picked up this impression from lots of different places, but I'd be happy to be corrected. I kind of assumed that it would take a very long time for the ocean to 'let go' of its extra carbon content back into the atmosphere. Especially since the only major 'sink' will be rock weathering, that takes a very, very long time. I'm thinking, for one, about the time scale graph just posted here.

    But then I seem to have a knack for totally misunderstanding the most stunningly obvious of graphs, charts and elementary science. So please do illucidate if I am straying far from the fold, here.

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  9. Wili,

    Here is a cite that supports your claim about ocean outgassing.  It was easy to Google.  It is expected in scientific discussion to produce cites to support your argument.  The moderator would be biased if he only asked skeptics to support their position.  It is very time consuming to find cites for all your claims.  The long posts that Tom and a few others make, with lots of cites, take a lot of work.

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  10. Willi @8, your original claim is ambiguous, and on its most natural interpretation, is wrong.  Specifically, if we were to cease all anthropogenic CO2 emissions, then the ocean would absorb more CO2 for about 300 years, reducing the atmospheric CO2.  Rather than outgassing, it would be ingassing.  After that, slower processes of will continue to reduce CO2 levels, but at a much slower rate.  Overall, it will take tens to hundreds of thousands of years to reduce the CO2 level back to preindustrial levels.  Here is a graph from 2008 showing the major processes, and approximate timescales:


    This process is shown be essentially all carbon models, although they vary slightly as to rate.

    Note, the models introduce the full anthropogenic load of CO2 in single pulse (ie, over one year), resulting in initial values of atmospheric concentration higher than have in fact been seen.  An earlier study (referenced here) used an earlier version of the Berner model to calculate the rate of reduction.  Integrating that rate with known fossil emissions showed a rate of CO2 rise comparable to the observed.  The initial take down that has already occured is inconsequential, however, for the long draw down.

    One point that does need to be noted is that these models also assume zero further emissions.  Emissions as low as 5-10% of current values will prevent the reduction of the CO2 concentration in the short term, and will lead to a gradual rise in CO2 in the long term.

    Finally, Michael Sweet's citation discusses the case in which all excess CO2 is removed from the atmosphere.  If, with CO2 raised to 500 ppmv, we reduce CO2 back to 280 ppmv (by a wave our our wand), then outgassing will occur, restoring CO2 levels back to about a quarter of the peak excess (ie, to about 340 ppmv).

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  11. Thanks, michael and Tom.

    Tom, you claimed: "if we were to cease all anthropogenic CO2 emissions, then the ocean would absorb more CO2 for about 300 years, reducing the atmospheric CO2."

    The first part of this statement is exactly what I meant by "once equilibrium is reached." It is interesting to know that this point would be reached, in an artificial model with no other carbon input, in about 300 years.

    But we aren't living in an artificial model. Permafrost carbon, at least, will continue to be released for a long time (MacDougal et al. 2012), and other carbon feedbacks are likely to kick in as well. I guess the 'good' news of that is that this will mean that the oceans would absorb atmospheric carbon for even longer, presumably.

    I confess that I was thinking of the equally artificial scenario that michael's citation discusses, particularly in light of the NRC report on 'Climate Intervention' (on which see here ). As we develop ways to extract CO2 from the atmosphere, even if we figured how to do it all in one fell swoop, we would then have to continue to deal with the CO2 the oceans would then offgas.

    One thing I did definitely overlook was the effect that a more acidic ocean would have on disolving which will allow the oceans to disolve more CO2, though at a terrible price.

    "Second, the more acidic water is, the better it dissolves calcium carbonate. In the long run, this reaction will allow the ocean to soak up excess carbon dioxide because more acidic water will dissolve more rock, release more carbonate ions, and increase the ocean’s capacity to absorb carbon dioxide. In the meantime, though, more acidic water will dissolve the carbonate shells of marine organisms, making them pitted and weak."

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  12. One more clarification (I hope) for now. It strikes me that the scenario that Tom's excellent source presents involves a sudden massive pulse of carbon. That will obviously give you a different value for how long it takes to get to atmosphere-ocean CO2 equilibrium than a scenario where all CO2 emissions stop immediately.

    I would think that in the latter scenario, equilibrium would be reached much sooner than in the former, but sometimes these things behave in counterintuitive ways.

    I would also think with ranyl, that increased water temperatures would also hasten the time it takes to reach equilibrium, but I imagine these models are taking that into account.

    It all points up to me how even things as seemingly straight forward as determining when CO2 gets into equilibrium between water and air can end up being much more complex than one might think (similar to how complicated it is to determine something as seemingly simple as the melt rate of ice to figure when Arctic sea ice will (mostly) melt out).

    Sorry if these ruminations are too rambling, and thanks again for the great links, especially the Tom's piece by Archer et alia.

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  13. LINK

    CO2 response to rapid removal Calderia

    How much CO2 can oceans take up (Scripps)

    Hi Wili,

    An Interesting thing the oceans, also looking a Tom's dramatic graph see the scale is 1000's of years (deep oceans will eventually take CO2 out of atmosphere, not they did in the past when it was warmer!), and in the short time periods things are very slow, and as you say as the PCO2 atmosphere drops the oceans will start to off gas as will the terrestial sinks (CO2 fertilzation falls away again). And these models rely on intact ecosystems and plankton species to keep the bio-carbon-pump going yet they are suspectible to high CO2 as well. And warming temeprature do decrease the how much CO2 the ocean can absorb, and warming tends to cause warming shoaling of the sea water keeping the colder water below the surface and booth affects decrease ocean uptake and can make it offgas, the warm tropical waters already off-gas CO2, it is the cold waters the are the sinks, and aren't the polar regions warming quite rapidly.

    And like you say permafrost releases, etc, etc, especially if CS higher than 3C and the Miocene blog this week,

    " Even allowing for that, the fact that models need a sensitivity of 4°C per CO2 doubling to recreate Mid-Miocene warmth suggests that the modern value is more likely towards the upper end of the IPCC range of 1.5-4.5°C than the lower end."


    And the (MacDougal et al. 2012), when CS was 4.5C despite complete cessation of emissions CO2, atmospheric CO2 rose and it does like CS is going to be on the high side as the evidence mounts up, and everyone just seems to be ignorign this paper where Pliocene average was ~275ppm;

    "We reconstruct atmospheric pCO2 for the Pliocene (3.3 to 2.8 Ma) of ~270 ±40 ppm (2σ) similar to Pleistocene interglacials. We record little or no variability suggesting pCO2 was persistently at about Pleistocene interglacial values. Only at the outer bounds of our uncertainty envelope would we record Pleistocene glacial levels of pCO2. Uncertainty in our assumptions for productivity, SST and cell size all result in a broad uncertainty envelope around our preferred parameterization, with our best 396 estimate suggesting pCO2 was between ~ 230 and 300 ppm."

    Badger M. et al (2013), High resolution alkenone palaeobarometry indicates relatively stable pCO2 during the Pliocene (3.3 to 2.8 Ma), Philosophical Transactions A,

    WHat does that mean for CS, and having CO2e of 460ppm!!!!

    Bottom line is the lags in the system mean we are going warm another ~0.7C whatever happens (remember the removal of the sulphur dioxide cooling umbrella if all fossil fuels stop being used, so there is definitive warming to come).

    In all the geological records when planet warms CO2 is released and we are warming, so that is very likely to happen again, and a lot of release is from the oceans.

    Also keep in mind if the CS is 4C, then all these policy maker advisorsory carbon budget papers, that use the raft of models where ~50% have a CS less lower than 3C, are ridiculously over optimistic, for all those models with a CS

    It seems to me the everything is pointing to a CS of ~4-5C and that CO2 levels will rise even if all emissions are stopped today, and from the Calderia paper above, the only way to lower the CO2 in a time frame needed (80% heating in 100years according to Hansen), is not only to stop all emissions but alos actviely remove CO2 from th eatmosphere. Soberingly in the Calderia paper even taking put all of man's historic emissions and stopping all emissions (CO2 fell to 275ppm innediately), the equilibrium CO2 still rose to 360ppm, and that took 5000 years, and last CO2was 350ppm wsas the early Pliocene, a different world, totally different weather patterns, higher ocenas, much warmer Arctic and a warmer tropical warm pool (that will relase CO2 of course)...and could go on but how much prrof do people need to see that unless CO2 emissions are stopped immediately almost and the biosphere enhanced massively to help bring CO2 out of the atmopshere, then 2C and more is inevtiable and that means a totally new world (no human has ever experienced before) for those who surive.

    And in the mean time flying is much more important!

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  14. wili @12, even after atmosphere/ocean quasi equilibrium is reached with regard to pCO2, the ocean will be a net sink for CO2 as the effect of chemical weathering occurs within the ocean.  So, even at "equilibrium", oceanic outgassing is not a problem unless we artificially lower CO2 levels by removing CO2 from the atmosphere (at which point we need also to remove the excess from the ocean).  Indeed, the most efficient way to remove CO2 from the atmosphere will likely involve accelerated chemical weathering by quarrying, crushing, then dumping suitable rocks in the ocean surface, so that we draw down atmospheric CO2 indirectly by drawing down oceanic CO2.

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  15. "the most efficient way to remove CO2 from the atmosphere will likely involve accelerated chemical weathering by quarrying, crushing, then dumping suitable rocks in the ocean surface, so that we draw down atmospheric CO2 indirectly by drawing down oceanic CO2."

    That's actually rather interesting. I hadn't thought about sequestration of ocean CO2 (basically of carbonic acid). Are there any proposals that have been made in that direction that you have links to?

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  16. willi @15, here is one proposal.  Treat it with caution as it has not been peer reviewed.  They estimate a cost of 10 Euros per tonne of CO2 sequestered, but because they are trying to sell the idea, I would definitely treat that as an underestimate, but it is likely to be cheaper than carbon capture and storage.  (It is, however, possible to use a variant of this technique to make CCS cheaper, and that may be a cheaper approach again.)

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