The terrestrial biosphere – a growing carbon sink

Over the course of time CO2 emitted to the atmosphere is sequestered in carbon sinks. There are two places it can go:

* Into the ocean sink, or
* Into the terrestrial biosphere sink (vegetation, soils etc.)

How much goes into each? I’m still looking into that. In the meantime I’m presenting some observational data which suggest that the terrestrial biosphere sink is growing rapidly and may be making a larger contribution than is generally supposed.

We begin with the monthly CO2 record for Point Barrow, Alaska. It shows an increase of about ~55 ppm CO2 between 1975 and 2008, which is within a few ppm of what CO2 records elsewhere in the world show, and the pronounced seasonal CO2 cycle characteristic of the Arctic. At first glance there’s nothing unusual about it. (Note: the unadjusted Scripps monthly CO2 data I used to construct the Figures in this post have now been overwritten by seasonally-adjusted monthly data, although daily data are still available):

Figure 1: Point Barrow CO2 record

But when we detrend the data and isolate the seasonal CO2 cycle, this is what we see:

Figure 2: Point Barrow seasonal CO2 cycle and seasonal cycle amplitude

Except for the outlier point in 1980 the amplitude of the seasonal CO2 cycle shows a straight-line increase from 14.7 ppm CO2 in 1976 to 17.6 ppm CO2 in 2006, a 20% increase over 30 years.

Do other records show the same thing? Figure 3 plots the seasonal cycle and amplitude data for the ten longer-term stations in the Scripps CO2 data set. The five Northern Hemisphere records (Alert, Barrow, La Jolla, Mauna Loa and Cape Kumukahi) all show appreciable seasonal CO2 ranges and straight-line increases in seasonal cycle amplitude (although interestingly Mauna Loa, the most widely-used, gives the most erratic results, most likely because of elevation. The record from Cape Kumukahi, which is located a short distance away at sea level, is much better-behaved). Christmas Island on the Equator shows a much smaller seasonal cycle and the four records in the Southern Hemisphere show hardly any seasonal cycle at all (all plots have the same vertical scale). American Samoa is the only record in the Southern Hemisphere that shows a detectable increase in seasonal cycle amplitude:

Figure 3: Seasonal CO2 cycles & amplitudes, all Scripps records

Station locations are shown on the map below:

How large are the increases when considered on a global scale? Figure 4 shows a global CO2 time series I constructed by averaging five records at latitudes that average out close to the Equator – Barrow, La Jolla, Christmas Island, Baring Head and South Pole, all of which have data between 1978 and 2006. The records track each other closely in terms of absolute CO2, with the Northern Hemisphere records showing a few more ppm than the Southern Hemisphere records and much larger seasonal cycles that are in antiphase to those in the Southern Hemisphere. The global mean plot, however, is dominated by Northern Hemisphere seasonal cycle.

Figure 4: Global CO2 series

Figure 5 shows the detrended global series. Over the 26-year period the amplitude of the global seasonal cycle increased by 22% from 4.9 to 6.0 ppm:

Figure 5: Global seasonal CO2 cycle and seasonal cycle amplitude

Figure 6 plots the Figure 5 seasonal cycle CO2 amplitudes against mean annual atmospheric CO2 concentration. The two are strongly correlated (R squared = 0.95, increasing to 0.98 when the outlier point at the bottom left – the 1980 Barrow data again – is excluded):

Figure 6: Seasonal CO2 cycle amplitude vs. atmospheric CO2 concentration

These results all point in one direction – increased atmospheric CO2 is causing the terrestrial biosphere sink, the bulk of which is in the Northern Hemisphere, to expand at a rate which is closely linked to the concentration of CO2 in the atmosphere. In other words, more CO2 is causing the terrestrial biosphere carbon sink to grow. The question is, how fast?

Well, what could have caused the amplitude of the global CO2  seasonal cycle to  have increased by 22% between 1978 and 2006? The simplest explanation is that the terrestrial biosphere was 22% larger in 2006 than it was in 1978. How much does this represent in terms of added carbon? The world’s vegetation is estimated to weigh around 600 gigatonnes, and 22% of that is 132 GtC, which over 28 years works out to an average increase in sink size of 4.7 GtC/year. Not peanuts.

Is this number realistic? Right now I have no idea, but based on my ongoing review of the annual global carbon balance data it may be the best one we are going to get.

This entry was posted in Climate change and tagged , , . Bookmark the permalink.

40 Responses to The terrestrial biosphere – a growing carbon sink

  1. Tends to support the notion that CO2 is a proxy for a vibrant biosphere, the more CO2, the more life present. However, given the composition of both the Venusian and Martian atmospheres, where CO2 is magnitudes higher in volume than the Earth, this becomes a problematical notion, and hence the notion must need be qualified with the phrase, “every thing else being equal”.

    My guess is that it’s the expanding biosphere that is causing the increase in CO2, purely on metabolic considerations. (Get an auditorium, pile it full of people and both the local temperature rises, as well as the CO2 content in the air).

    There is an idea that populations that experience frequent catastrophic reductions in numbers tend to compensate by increasing population numbers so that the next time something happens, another culling event as it were, sufficient numbers are left to repopulate afterwards.

    This seems a plausible model for the present human population explosion when many anticipate a climate catastrophe, or when others expect a second coming of some or other individual. So there we have it – a global biospheric anticipation of another calamity – the numbers are increasing, vis. population, biosphere and CO2 and there’s the psychological anticipation as well of the ending times in all its myriad of variations and expectations. The only conundrum is whether its only humans who are anticipating the coming catastrophe, or the biosphere in general, as the CO2 data seems to suggest.

  2. Dave Rutledge says:

    Hi Roger,

    An impressive post. Among the stations that you plotted, the one that is at the most important latitude for agriculture is La Jolla. That is a massive 42% increase over 40 years. What are the implications for agricultural yield, assuming that farmers can supply nitrogen as needed?


  3. Phil Chapman says:

    Interesting data, Roger. I was especially interested in the noisy data from Mauna Loa, which raises the question: if you were trying to monitor changes in global atmospheric CO2, would you place your instruments atop an active volcano?

    There is plenty of evidence that from satellite and other measurements that net primary productivity (the difference between carbon uptake in photosynthesis and loss by plant respiration) is rising steadily, especially in arid areas. For a comprehensive survey, see . CO2 is unquestionably good for plant productivity; that is why greenhouse agriculture uses elevated levels.

    • Phil: Interesting question. The Mauna Loa observatory was in fact evacuated for a couple of months in 1964 because of an eruption.

      But I don’t know whether CO2 emissions are what cause the irregularity in the seasonal CO2 cycle. I suspect it may have more to do with whether the wind is blowing uphill or downhill from the coastal forests. In terms of absolute CO2 Mauna Loa is a close match to records elsewhere in the world.

      • Yvan Dutil says:

        Mauna Kea is is middle of ocean. hence, the CO2 is more sensitive to the water temperature thant ten biological cycle. It is rather easy to avoid the local contamination by the volcano. Also, this site is mostly upwind from the volcano. Geophysicist are not stupid.

  4. clivebest says:

    This via Matt Ridley:

    The latest and most detailed satellite data, which is yet to be published but was summarized in an online lecture last July by Ranga Myneni of Boston University, confirms that the greening of the Earth has now been going on for 30 years. Between 1982 and 2011, 20.5% of the world’s vegetated area got greener, while just 3% grew browner; the rest showed no change.

    So that confirms independently an increase in global photosynthesis of about 20%. The satellite resluts are based on NDVI Normalised Digital Vegetation Index. This is basically how green each pixel is in the growing season viewed from space.

    • Willem Post says:


      It looks like the increase in biosphere CO2 absorption is largely in the Northern Hemisphere, where are most of the people and most of the GW has taken place.


      I can attest to that from personal observation.

      Our house in Norway is located on the Oslo Fjord in Vestfold, Norway, next to the north border of the Borre National Park where is the largest collection of Viking graves (Yngling Dynasty).

      From our bedroom, we could see the large mounds and see the center meadow area in the middle of the park.

      Starting around 1985 that view became less and less due to more and more undergrowth among the trees. At present, it has become impenetrable. Just a green wall. All mounds have become invisible.

      In addition, the climate has gotten warmer. Frequently, I used to wear sweaters in summer, now it is rarely necessary, and swimming is more pleasant, as the water temperature of the Fjord has increased.

      • Euan Mearns says:

        Willem, so you stay in Oslo? I stayed there 1983 to 1991, beautiful city back then. One of the things we enjoyed most were the long hot summers. Swimming in the Fjord out at Sandvika, I recall one year as late as October the water was still warm enough to swim. And then it would freeze up in winter. I stayed up on Ekebergsletta.

  5. Euan Mearns says:

    Roger, fantastic data and charts. I calculate that your emissions model has 207GtC from 1978-2006 (29 years). 44% of those are still in the atmosphere, hence 112GtC have bee sequestered a figure that is probably within error of your growth in the terrestrial biosphere – 132GtC.

    Why do your data stop in 2008?

    One thing that makes me uneasy is the fact that Point Barrow and Alert are a million miles away from vibrant forest – especially Alert. Hence I wonder if photosynthesis is the sole cause of the annual cycle and amplitude growth with time.

    This is not very scientific, but I do get the feeling here that our woodlands are incredibly lush in summer time with spectacular growth of young trees. Can the terrestrial biosphere go on expanding forever.

    • Roger Andrews says:

      Euan: Why do my data stop in 2008? Probably because this is as far as Scripps had gotten at the time (I downloaded them a few years ago)

      One thing that makes me uneasy is the fact that Point Barrow and Alert are a million miles away from vibrant forest – especially Alert. CO2 mixes very rapidly in the atmosphere. The vibrant forests that supply the CO2 to Barrow and Alert are somewhere else. The only place CO2 gets hung up is along the Equator. The video below gives details 🙂

  6. A C Osborn says:

    Eaun, you have also not included the reduction in CO2 sequestration lost due to de-forestation and Jungle clearing for bio mass and bio fuel.

    • AC: The CO2 seasonal cycle data sum the impacts of growth and deforestation on the size of the terrestrial biosphere sink. They indicate that deforestation in some areas is being overwhelmed by growth in others.

      • Yvan Dutil says:

        Actually, the annual cycle is increasing. This is not the same thing as the total photosynthesis because the cycle is much smaller near the equator. I think you can only conclude that vegetation is going north in average.

  7. A related issue that I didn’t go into but probably should have is what the seasonal carbon cycle over the ocean looks like. According to the graphic below it’s negligible in comparison to the land cycle:

    • dennis coyne says:

      Hi Roger,

      What is the source for the chart above. How do we know which carbon is taken up and released by the land vs the ocean, Carbon dioxide gets fairly well mixed in the atmosphere so it would seem difficult to separate the two.

      The assumption that the flux is proportional to the size of the sink may be incorrect. The flux has increased by about 22% while the atmospheric sink has increased about 12% over the same period, what has happened to the size of the land sink cannot be inferred from this data, it may be larger, smaller or may have remained the same. The estimates of the land sink are quite difficult and there is a high degree of uncertainty in these estimates. If we take the earth system as a whole, the estimates of carbon flow to the atmosphere from fossil fuels and cement production are pretty good, land use change is less certain, and changes in the amount of carbon in the atmosphere are pretty good. How the flux to the land plus ocean is divided between the land and ocean is not very precise.

  8. clivebest says:

    The amount of carbon in land vegetation is equal to the total weight of plants. This carbon taken out of the atmosphere is not sequestered permanently. 99% of the carbon is released back into the atmosphere when the plant dies or is eaten by animals. There is always about the same amount of Carbon in plant life as there is CO2 in the atmosphere. All that happens with (anthropogenic) CO2 fertilization of photosynthesis is that the total live biomass increases towards the atmospheric content.

    The roots of plants however allow CO2 to enter soils where weathering of igneous rocks can take place. These eventually are washed down into the sea and form sedimentary rocks over millions of years. The only semi-permanent sink is limestone -Calcium Carbonate.

    Yet even this sink is not permanent. Plate Tectonics acting over 10s of millions of years eventually recycles the buried CO2 in sedimentary rocks through Volcanoes and mid ocean ridge vents. The amount of CO2 in the atmosphere is fine tuned to balance the rock weathering rate against input of CO2 from Volcanoes. This rate also keeps the earth’s temperature perfect for life – especially plant life !

    Amazingly, plate tectonics also recycles the minerals like phosphorous that are essential for life. Without this the oceans would run out of minerals and photosynthesis would stop.

    • Euan Mearns says:

      Clive, you are reading from the AGW script here. The amount of HCO3- entering rivers as a result of rock weathering is minuscule compared with the annual ocean – atmosphere flux. Why should it have any significance? I don’t buy that whole rock weathering global thermostat thing. For a start most of the crust that is subducted is oceanic crust. Its really pretty hard to subduct continental crust – and that’s where all the limestone is. It is estimated that sedimentary rocks contain 100,000,000 GtC. Where did it all come from if the system is in some form of fine balance? Some of that exists at CaCO3 but a huge chunk of it is as semi-reduced plant material – the kerogen of shale gas and the like.

      I agree that increasing the mass of plants is a non-permanent sink – you should have a look at my previous post on this. Future trajectory will depend on fate of that organic material, how much enters soils as biodetritus and how much is recycled quickly into the atmosphere.

      • dennis coyne says:


        The fate of the carbon in the soil and ocean is important. By focusing only on photosynthesis, you ignore the recycling of this carbon back into the atmosphere. This is what the single exponential model which you seem to favor misses, and which the models of climate science accounts for. The Bern model is a simplification of the more complete physical models. The flow of dissolved inorganic carbon from the deep ocean to the atmosphere and the limited buffering capacity of the ocean and its effect on the calcium carbonate cycle (not a part of the rock weathering story, it is called the carbonate pump).

        • Euan Mearns says:

          Dennis I’m not ignoring it, merely pointing out that this is at least two stage process and needs to be modelled as such. Roger’s post suggests that maybe all the sequestered C is going to terrestrial biosphere. If this is the case, and deep oceans not involved in sequestering excess CO2 then Phil Chapman’s equilibrium model kicks back in. This is iterative blogging trying to get to grips with what may actually be going on.

          • dennis coyne says:

            Hi Euan,

            You talk about it so in that sense it is not ignored. In a model that assumes that only photosynthesis matters for determining atmospheric carbon dioxide levels, the other processes are effectively set aside for some later model which is never produced.

            What does this miss? The relatively large flows of carbon from the ocean to the atmosphere from dissolved inorganic carbon (which is more than just bicarbonate) as carbon rich water upwells from the deep ocean. In addition carbon dioxide is released from the formation of calcium carbonate and this is also an important part of understanding the earth system carbon cycle.

            The oceans are very much involved in the sequestering of excess CO2.

            An alternative hypothesis for the larger amplitude of the seasonal CO2 cycle is that forests have been cleared to expand agricultural output.
            Over the period of Roger’s analysis world population has grown by 55%, due to improved productivity in agriculture a 55% increase in food output (assuming average per capita food consumption was unchanged) could be handled by only a 22% increase in land devoted to farming/pastures. The 22% increase in the amplitude of the seasonal cycle may have been accompanied by a net decrease in the carbon sequestered by land ( due to a possible decrease in tree growth from forest clearing for farms and pastures).

            There is also afforestation to consider as forests regrow in areas previously cleared for farms or pastures. On balance even if the total forested area has not changed, more intensive farming and grazing to feed the larger population could account for much of the change in the seasonal changes in atmospheric CO2 with very little change in the net annual carbon sequestered on land.



          • Dennis:

            Everyone but you and the IPCC seems to agree that the size of the terrestrial biosphere sink is expanding – even the IPCC did at one time. The TAR in fact reported a sevenfold increase in land carbon uptake in the space of a decade. I quote from Section 3, Executive Summary:

            For 1980 to 1989, the ocean-atmosphere flux is estimated as -1.9+/- 0.6 PgC/yr and the land-atmosphere flux as -0.2 +/-0.7 PgC/yr based on CO2 and O2 measurements (negative signs denote net uptake). For 1990 to 1999, the ocean-atmosphere flux is estimated as -1.7 +/- 0.5 PgC/yr and the land-atmosphere flux as -1.4 +/- 0.7 PgC/yr.

            An expanding biosphere is also in line with the conclusions reached by the numerous scientists who have studied the issue and whose results were synthesized by Idso (2012), a publication with which you should be familiar.

            A case can in fact be made that enhanced vegetation growth is so far the ONLY observationally-demonstrated impact of increased atmospheric CO2.

          • dennis coyne says:

            Hi Roger,

            There is also the increased temperature and pH of the Ocean. The science improves over time. The scientists who study this think there is a great deal of uncertainty about the size of the land sink and that it has changed very little since 1765.

            The data you have shown indicated that there are large seasonal fluxes to the land and then back to the atmosphere. The leap that this means the land sink has increased is speculation, pure and simple.

    • The amount of carbon in land vegetation is equal to the total weight of plants.

      The chemical equation for photosynthesis is:

      6CO2 + 6H2O ——> C6H12O6 + 6O2

      Assuming the 6O2 fraction is lost to the air then the sum of the atomic weights on the right side of the equation is 180, of which carbon makes up 72, i.e. 40%.

      If I’ve done this wrong, well, chemistry was always my worst subject. 😉

      • dennis coyne says:

        Hi Roger,

        Most of the C6H12O6 gets broken down into CO2 and H2O, the CO2 flows back to the atmosphere.

    • Euan Mearns says:

      And as plants absorb CO2, this has led to overestimates of how much of the greenhouse gas is left in the atmosphere.

      From the Daily Mail. In fact it leads to an over estimate of how much the oceans take up.

      PS this is Roger’s post 🙂

    • What I found most interesting wasn’t the paper itself but the “expert reactions” to it. The impact is supposedly “slight”, but already the consensus is busy circling the wagons. Either no apostasy is too small to be ignored or there’s more going on here than meets the eye:

      The expert reactions also include a couple of particularly choice comments from Simon Lewis:

      This new analysis suggests that some modelling studies slightly underestimated the size of this major free subsidy from nature over the past 100 years.

      I think nature is getting a major free subsidy from us.

      Many scientists think climate models are too optimistic about how much carbon dioxide forests can take up. Few think trees will grow ever-bigger as they are fertilized by ever-higher amounts of carbon dioxide in the atmosphere.

      Translation: We can believe climate models when they tell us what we want to hear but not when they don’t.

      But hats off to Richard Betts for admitting that carbon cycle models are deficient.

  9. Drjip says:

    One of the factors that your rather nice graphical exposition does not highlight is the fundamental synergism between plant net primary production (NPP) and other major perturbation of a global geochemical cycle – namely the anthropogenic addition of reactive nitrogen Nr produced by the Haber-Bosch process., and that due to the burning of fossil fuels, primarily oil.

    The two major consequences of Nr are acidic deposition leading to nitrogen saturation of northern temperate forest ecosystems, as well as increasing eutrophication of freshwaters and continental shelf waters.

    Some useful papers are:

    W. de Vries, et al. The impact of nitrogen deposition on carbon sequestration by European forests and heathlandsOriginal
    Forest Ecology and Management, Volume 258, Issue 8, 25 September 2009, Pages 1814-1823


    Svein Solberg et al. Analyses of the impact of changes in atmospheric deposition and climate on forest growth in European monitoring plots: A stand growth approach.
    Forest Ecology and Management, Volume 258, Issue 8, 25 September 2009, Pages 1735-1750

  10. Drjip says:

    The impact of reactive nitrogen (Nr)deposition on plant growth and freshwater eutrophication also provides an important synergistic feedback on carbon sequestration and Net Primary Production (NPP).

    Evidence suggests that the growth (NPP) of temperate northern forest is being slowly increased through the fertilizing impacts of NH4 and NO3 via acidic deposition, which the Critical Loads approach has been tackling over the last 20 odd years.

    Two papers that address this issue of increased carbon sequestration are

    De Vries et al.2009 The impact of nitrogen deposition on carbon sequestration by European forests and heathlands Forest Ecology and Management, Volume 258( 8,): 1814-1823


    Solberg et al 2009 Analyses of the impact of changes in atmospheric deposition and climate on forest growth in European monitoring plots: A stand growth approach
    Forest Ecology and Management, Volume 258 (8): 1735-1750

  11. Pingback: Climate Change

  12. Pingback: AWED Energy & Environmental Newsletter: October 20, 2014 - Master Resource

  13. Pingback: Recent Energy And Environmental News – October 20th 2014 | PA Pundits - International

  14. All the inner planets except Venus are within a few percent of the computed gray body temperature in their orbits , . Mars is way below the 273.15K freezing point of water which is the obvious tipping point for life . The graybody temperature in our orbit is only about 279K , and we’re about 10K warmer than that .

    Venus’s surface temperature is 2.26 times the 328K gray body temperature in it’s orbit . Unless you can overcome the divergence theorem , it would have to be 10 times as reflective in the IR as aluminum for that to be due to a “greenhouse effect” : .

    Bob Armstrong

Comments are closed.