Earth system models underestimate carbon fixation by plants in the high latitudes

From Nature Communications.

Abstract

Most Earth system models agree that land will continue to store carbon due to the physiological effects of rising CO2 concentration and climatic changes favoring plant growth in temperature-limited regions. But they largely disagree on the amount of carbon uptake. The historical CO2 increase has resulted in enhanced photosynthetic carbon fixation (Gross Primary Production, GPP), as can be evidenced from atmospheric CO2 concentration and satellite leaf area index measurements. Here, we use leaf area sensitivity to ambient CO2 from the past 36 years of satellite measurements to obtain an Emergent Constraint (EC) estimate of GPP enhancement in the northern high latitudes at two-times the pre-industrial CO2 concentration (3.4 ± 0.2 Pg C yr−1). We derive three independent comparable estimates from CO2 measurements and atmospheric inversions. Our EC estimate is 60% larger than the conventionally used multi-model average (44% higher at the global scale). This suggests that most models largely underestimate photosynthetic carbon fixation and therefore likely overestimate future atmospheric CO2 abundance and ensuing climate change, though not proportionately.

Introduction

Predicting climate change requires knowing how much of the emitted CO2 (currently ~40 Pg CO2 yr−1) will remain in the atmosphere (~46%) and how much will be stored in the oceans (~24%) and lands (~30%)1. Earth system models (ESM) show a large spread in projected increase of terrestrial photosynthetic carbon fixation (GPP)2,3,4,5,6 and are thought to overestimate current estimates5,7, although the latter is also subject of debate5,8,9,10,11. Historical increase of atmospheric CO2 concentration, from 280 to current 400 ppm, has resulted in enhanced GPP due to its radiative12 and physiological13,14 effects, which is indirectly evident in amplified seasonal swings of atmospheric CO2 concentration15,16,17 and large scale increase in summer time green leaf area18,19,20. Thus, these observables, expressed as sensitivities to ambient CO2 concentration, might serve as predictors of changes in GPP21,22,23,24 and help to reduce uncertainty in multi-model projections of terrestrial carbon cycle entities.

This study is focused on the northern high latitudes (NHL, north of 60°N) where significant and linked changes in climate25 and vegetation15 have been observed in the past 3–4 decades: 52% of the vegetated lands show statistically significant greening trends over the 36-year record of satellite observations26 (1981–2016, Methods), while only 12% show browning trends, mostly in the North American boreal forests due to disturbances27 (Fig. 1). We therefore hypothesize that the greening sensitivity (i.e., leaf area index, LAI, changes in response to changes in the driver variables) inferred from the historical period of CO2 increase can be used to obtain a constrained estimate23 of future GPP enhancement from both the radiative and physiological effects (Supplementary Fig. 1).

Fig. 1

figure1

Greening (LAI increase) and browning trends during 1981–2016 in the northern high latitudes. Statistically significant (Mann–Kendall test, p < 0.1) trends in summer (June–August) average LAI are color coded. Non-significant changes are shown in gray. White areas depict ice sheets or barren land. Details of the LAI data set are provided in Methods. The figure was created using the cartographic python library Cartopy (Release: 0.16.0)

Full size image

State-of-the-art fully coupled carbon-climate ESMs vary in their representation of many key processes, e.g., vegetation dynamics, carbon–nitrogen interactions, physiological effects of CO2 increase, climate sensitivity, etc. This results in divergent trajectories of evolution of the 21st century carbon cycle4,5,6. To capture this variation, we use two sets of simulations28 available from seven ESMs23 from the Coupled Model Intercomparison Project Phase 5 (CMIP5)—one with historical forcings including anthropogenic CO2 emissions for the period 1850–2005 and the second with idealized forcing (1% CO2 increase per year, compounded annually, starting from a pre-industrial value of 284 ppm until quadrupling). In our analyses, the magnitude of the physiological effect is represented by the CO2 concentration and the radiative effect by growing degree days (GDD0, > 0 °C, Methods) as plant growth in NHL is principally limited by the growing season temperature12. Leaf area changes can be represented either by changes in annual maximum LAI (LAImax)29 or growing season average LAI—we use the former because of its ease and unambiguity, as the latter requires quantifying the start- and end-dates of the growing season, something that is difficult to do accurately in NHL30 with the low-resolution model data.

Here, we apply the concept of Emergent Constraints (EC) to reduce uncertainty in multi-model projections of GPP using historical simulations and satellite observations of LAI focusing on NHL. We find that the EC estimate is 60% larger than the commonly accepted multi-model mean value, in line with a recent study that assessed the impact of physiological effects of higher CO2 concentration on GPP of northern hemispheric extra-tropical vegetation23. Detailed independent analyses of in-situ CO2 measurements and atmospheric inversions imbue confidence in our conclusions. Our central finding is, the effect of ambient CO2 concentration on terrestrial photosynthesis is larger than previously thought, and thus, has important implications for future carbon cycle and climate.

Full article here with no paywall.

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34 thoughts on “Earth system models underestimate carbon fixation by plants in the high latitudes

  1. Timely post as I just finished with ensuring a few fire brakes are as low to the earth as practical. It’s been one wet cool spring and with end of the permanent drought in the foothills, the mass of green stuff has been rather tuff to manage. This is the latest I have seen miners lettuce under the oaks in 20 years.

    The nitrogen fixing clover is still growing strong in many places but the invasive Russian nap weed is doing even better in some places. There is no truth to the rumor that CARB has fit drones with sensors to measure co2, ozone and particulate matter in the rural areas of the state (as part of the carbon capture and AQI programs).

    • CARB does NOT “need” real atmospheric data from UAV-borne remote sensors.
      They have their pagan religious dogma and climate scriptures to tell them what is true.

      No doubt kakatoa, that due to your apparent climate apostasy, your assignment to Climate Re-education Camp-7 is being processed in Sacramento as I write this.

      • Hillary calling millions of people “deplorable” resonated. Yet, for some reason, her “irredeemable” insult didn’t, even though it was much worse. Why bother sending someone that is irredeemable to a re-education camp? Why not just off them and put them out of our misery?

        • “Why not just off them and put them out of our misery?” vs their misery that Khrushchev covers a bit in a couple sections, The Terror and the Purge Years, of Khrushchev Remembers.

  2. “To capture this variation, we use two sets of simulations available from seven ESMs from the Coupled Model Intercomparison Project Phase 5 (CMIP5)—one with historical forcings including anthropogenic CO2 emissions for the period 1850–2005 and the second with idealized forcing (1% CO2 increase per year, compounded annually, starting from a pre-industrial value of 284 ppm until quadrupling).”

    Please NO MORE MODEL SIMULATIONS

    • Alan,
      You should actually read something before you comment.

      They use those 7 earth-system (ES) models as representatives of the CMIP5 ensemble. Their Leaf Area Index data came from over 35 years of real satellite observations. Then they compare observation to simulation to show the ES simulations that estimate carbon fixation are indeed majorly wrong.
      That is how science should work. Where it is broken is that climate modellers refuse to acknowledge observations and that the models are abject failures and continue on with their Cargo Cult inter-comparisons in pursuit of Rent.

      • Thus, these observables, expressed as sensitivities to ambient CO2 concentration, might serve as predictors of changes in GPP21,22,23,24 and help to reduce uncertainty in multi-model projections of terrestrial carbon cycle entities.
        https://www.nature.com/articles/s41467-019-08633-z

        I suppose “these observables” might serve as predictors of other changes too, like climate heating.

        • No one in the climate debate is suggesting, all other things held unchanged, that an increase in CO2 won’t lead to higher DWIR, a rise in the ERL, and thus a slightly warmer surface. In a perfectly blue sky model of the Earth atmosphere even with deep oceans and water, this would lead to a warmer surface that would be captured by models of radiative transfer.

          The problem is the Earth climate system is far more complex than that. We receive just enough radiant solar energy to maintain steamy tropics and vast ice sheets at the poles, and short wave opaque clouds of water vapor at all latitudes. A Goldilocks climate if you want.
          So nothing is actually constant in our ever changing climate. Feedsbacks exist at all time scales from minutes to millenia to epochs. Our world is far from a Blue Sky model of climate. Clouds, seasonal heating-cooling, diurnal cooling, ice caps shrinking expanding both with the seasons and with the years at levels the models fail to predict.

          All that screams that the AOGC models are mere contivances of modeller bias and any belief they say anything about 40 to 80 years from now is absurd.

          So for the climateers to believe their cargo cult models tell them of runaway greenhouse effects is laughable… to honest scientists.

          • No one,you start with,Joel. But the real someone’s began with Poisson and Maxwell. They now include Astrophysics in general because that science relies on the Ideal gas laws and pressure alone to raise gas clouds from 3K to Star ignition temperature. Gas specie is irrelevant, as on Earth. Only mass pressure and solar irradiance matter, to real physics. Model control knobs could not matter less if they were made of the proverbial goat droppings.

          • No one,you start with,Joel. But the real someone’s began with Poisson and Maxwell. They now include Astrophysics in general because that science relies on the Ideal gas laws and pressure alone to raise gas clouds from 3K to Star ignition temperature. Gas specie is irrelevant, as on Earth. Only mass pressure and solar irradiance matter, to real physics. Model control knobs could not matter less if they were made of the proverbial goat droppings. Brett Keane

  3. You can safely ignore this nonsense. The science has all been settled for some time now so this is obviously rubbish.

    • These people also need to be locked up. We wouldn’t want any opposing viewpoints voiced since we know the debate is over. After all, we’re the only ones who understand what science is: not these thousands of scientists that study this GPP? They’re obviously all paid off by the fossil fuel industry. We need less production so people can be more dependent on our friends the globalists. They’re the only ones who can save us from CACC. Thank you for pointing that out Kerry.

  4. Ok, they identified their data and their tools and didn’t paywall the study. Moreover, the findings contradict some current speculations about sequestration, and are likely to be replicable/falsifiable. Right or wrong, it looks like science to me, and we need more science in this field , so congratulations to the authors.

    • A climate scientist is also happy while getting paid to crawl in the soot:

      Though I spends me time
      In the ashes and smoke
      In this ‘ole wide world
      There’s no happier bloke

  5. This study only addresses the boreal areas north of 60 deg N latitude.

    A study by NASA in 2016 said that CO2 greening is happening all over the planet, not just in the high north.

    https://www.nasa.gov/feature/goddard/2016/carbon-dioxide-fertilization-greening-earth

    And:

    https://notrickszone.com/2019/01/16/700000-square-kilometers-of-added-green-vegetation-climate-change-shrinks-sahara-desert-by-whopping-8/

    Of course the climate alarmists have done their best propagandizing to try and debunk the data and models behind vegetative greening .. but the data are still the data. They fall back on “don’t believe your lying eyes!”

    • Not entirely true.
      See this paper’s Supplemental Figure 6.

      In the Supplement they wrote:
      “Based on this result, also on global scale a substantial underestimation of photosynthetic carbon fixation is present –constrained estimate is 44% higher than multi-model mean indicated by green cross (56% excluding outlier).”
      And they show the reason in Supp Fig 6.

    • “[ ] on global scale a substantial underestimation of photosynthetic carbon fixation is present –constrained estimate is 44% higher than multi-model mean indicated by green cross (56% excluding outlier).”

      needs

      more super computers
      more super computers processing times

      needs

      more PV
      more Windelecs

      in times of de-hydrocarbonisation.

      _____________________________________

      We should giv’em 12 more years.

  6. LAI was determined as follows (from Methods):
    The new version (V1) of the LAI data set is an update of the widely used LAI3g data set26. It was generated using an artificial neural network (ANN) and the latest version (third generation) of the Global Inventory Modeling and Mapping Studies group (GIMMS) Advanced Very High Resolution Radiometer (AVHRR) normalized difference vegetation index (NDVI) data (NDVI3g).

    https://noaasis.noaa.gov/NOAASIS/ml/avhrr.html

    The NDVI is calculated from actual observations satellite observation in visible light compared to near-IR light.
    The pigment in plant leaves, chlorophyll, strongly absorbs visible light (from 0.4 to 0.7 µm) for use in photosynthesis. The cell structure of the leaves, on the other hand, strongly reflects near-infrared light (from 0.7 to 1.1 µm). The more leaves a plant has, the more these wavelengths of light are affected, respectively.
    https://en.wikipedia.org/wiki/Normalized_difference_vegetation_index

    The AVHRR flies on polar orbiting satellites NOAA-15, 18, 19, MetOps-A&B. (NOAA 16-17 have ceased operations).
    https://en.wikipedia.org/wiki/Advanced_very-high-resolution_radiometer
    https://noaasis.noaa.gov/NOAASIS/ml/avhrr.html

    So they use real observation to compare to what the modellers think is happening via their simulations.
    They decisively show that most earth systems models underestimate carbon fixation in the high latitudes.
    The CMIP5 models try to model vegetative response to increasing CO2 and greening. This paper simply shows 2 of the 3 compared models gets it wrong (CESM1(BGC) is NCAR-Boulders, and HadGEM2-ES from Hadley Centre). Only the Japanese JAMA Miroc-ESM model got it close.

    The authors final concluding sentences need emphasis:
    “The tendency for GPP underestimation in NHL by models reported here is also seen at the global scale (Supplementary Fig. 6). This, together with another recent study23, suggests that most models are underestimating photosynthetic carbon fixation by plants and thus possibly overestimating atmospheric CO2 and ensuing climatic changes2,4,6.”

    Climate Models and most Earth-Systems models are junk science garbage outputs. They are used a bias confirmation by the practitioners. It’s all Cargo-Cultism practiced at the highest levels with lots of public funding.

    This is in everyway similar to what has and IS happening with OCO-2 observations. NASA had this marvelous model of what they thought CO2 sink and source fluxes would look like pre-OCO-2 data. Now they have almost 5 years of OCO-2 data, and those earlier simulations are clearly junk.

    But the junk simulations were worse than true junk. Bad prior simulations (Cargo Cultism) induce Negative Learning. That is they taught use bad ideas that went into text books, faulty learning that must now be un-learned before a fresh perspective properly assess and understand what is the actual data is saying..

    See we see negative learning from junk CO2 flux models via data now from OCO-2. Now negative learning from junk Earth-Systems models on vegetative greening via actual data from AVHRR analyses of LAI (this paper). It is just a matter of time before the whole climate modeling junk is exposed as a really bad historic level of negative learning about GHGs and Earth’s temperature response to them as well.

    • Joel O’Bryan,

      I find your quoted text about IR reflection from Wiki somewhat at odds with my experience.
      I figured that plant leaves being thin bags of mostly water they would take up IR well.
      So in order to get my plants off to an early start in the morning (especially on cold winter mornings in a unheated greenhouse), before dawn I would have an IR lamp on a timer (and dimmer) to warm the plants. And warm the plants it what it did, the leaves especially would warm. Certainly they would be warmer than the air or soil about them when I did this.
      Now maybe the difference is that the lamps I used (controlled with a dimmer so as not to overheat the leaves) would put out longer wavelength IR but warm the leaves it certainly did.
      That was a long while ago, before all this fancy grow-light technology came in. Back when I lived in the cooler Northern Europe (cooler temperate region). IMO plants would probably naturally use the early morning sun’s LW IR output to get their enzymes for the photosynthesis process warmed and ready.

      • “I figured that plant leaves being thin bags of mostly water they would take up IR well…”

        What you figure and what actually happens are apparently two different things.

        Sort of like how ancient Greeks figured out everything was made of earth, fire, water, and air from simple observation, and it just snowballed for almost 2,000 years from there.

        Today the same kind of magical observation creates the “Earth’s gonna fry” porn from a minor increase of a trace gas stories. Science is supposed to be the scythe to such rubbish weeds of fake knowledge, but when the science itself becomes politicized, then anything can happen, from Lysenkoism, eugenics, to CAGW attribution and extreme weather beliefs..

        • Sorry but 3 years of growing plants (for winter soft fruits — strawberries, raspberry, etc.) in this manner worked very well.
          Lysenkoism or not, I know it worked and helped me get some an income.

    • Joel

      I was asking someone in Montreal last week who can work out such things, so I will ask you as well:

      When dealing with CDM projects covering biomass, the value of carbon dioxide reduction certificates (CERs) is based in part on the fraction of non-renewable biomass (fNRB) harvested in a region of nation. It serves as the baseline: the higher the fraction of fNRB, the higher the payoff in terms of carbon emissions reduced if the function (like cooking) can be made more fuel-efficient. There is a default value of 0.30 for the planet (which can be used for project calculations in the absence of any other information about biomass growth). It means 30% of wood harvested doesn’t grow back, on a global basis.

      The question arises: After the GPP increases by 43%, the growth of “what remains or grows back” will exceed the excess harvest and the biomass total will be in balance with the offtake. What will the CO2 concentration have to be to reach this illustrious target?

      Once achieved, all harvesting of biomass will be indefinitely sustainable because it will be replaced annually, at least on a global basis.

      The value of CER’s will drop to zero as the fNRB value will be 0%. I am pretty sure this fact of nature has not been considered in the UNFCCC’s CDM methodologies AMS-II.G. If the concentration increased 4-fold to 1200 ppm, would the GPP increase 43%?

      Thanks

    • “That is they taught use bad ideas that went into text books, faulty learning that must now be un-learned before a fresh perspective properly assess and understand what is the actual data is saying.”
      >>

      Religions don’t give up so easily, expect a holy crusade or three.

  7. That’s not even getting to the micro algae in the liquid 71 percent of the surface area.

    • NDVI technique only works on land plants unfortunately. Sea water residing green algae (phytoplankton really) turns the water greener as we can see with our color-adept human eyes, but NDVI is a comparison between the absorption of red light (0.5 to 0.7 micron) and the reflection of Near-IR (~1 micron) by the leaf. Water however absorbs strongly the Near-IR (and thermalizes it in a thin skin layer) so their is almost zero Near-IR reflected.

      However there are of course other multi-spectral methods to measure primary productivity (chlorophyll levels) of the oceans.
      https://aquila.usm.edu/cgi/viewcontent.cgi?article=4559&context=fac_pubs

  8. So, increased availability of food (to plants) results in increased growth and more food consumed than before. Who would have guessed? /sarc

    But it is good to see a number put to it. Honestly though, this should not be a surprise to anybody.

  9. They are saying that it’s not as bad as we thought?

    Must be a mistake. That’s not a permissible conclusion in climate science. More likely they’ve been secretly funded by oil and gas and coal companies.

  10. “Although the Arctic represents only a small fraction of the terrestrial biosphere, the rapid climatic changes in NHL and uncertainties associated with the net carbon balance emphasize the need for further detailed analysis. The tendency for GPP underestimation in NHL by models reported here is also seen at the global scale. This, together with another recent study, suggests that most models are underestimating photosynthetic carbon fixation by plants and thus possibly overestimating atmospheric CO2 and ensuing climatic changes”

    Wow. Is this the start of the climbdown? Climate Science is actually admitting they might have primed their models with junk data? I must be dreaming..

  11. An interesting read, but it still contains the usual mantra of the Church of Climate: ‘Uncertainties are large, we were wrong before, but we are still confident in ourselves.’

  12. “Here, we apply the concept of Emergent Constraints (EC) to reduce uncertainty in multi-model projections of GPP using historical simulations and satellite observations of LAI focusing on NHL.” Should have applied that concept to the mother computer program a half century ago.

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