Saturday, October 07, 2006


Having got into the CO2 pit with the good Diplom Beck (aka Anon), Eli was idling his time away sucking Saturday beers and reading the CDIAC CO2 mixing ratio records. (Of course E has better things to do, why do you think he was looking at CDIAC data?) While there is much there with which to bedevil the good Diplom, a more interesting thought occurred.

If one looks at the Mauna Loa CO2 record (taken with a continuous not a cryogenic method btw DB)

the seasonal variation is easy to see. More interesting is to compare the Mauna Loa seasonal variation with that observed at Barrow Alaska

and Bering Head, New Zealand

The decrease in seasonal variation as one moves north to south is obvious. In the northern hemisphere there is a great deal of land that blooms in the spring and summer. The large increase in vegetation which contributes to photosynthesis (and the warmer temperatures) noticably reduce the CO2 mixing ratios. The effect is most extreme in the far north. On the other hand, there is much less land and change in temperature during the year in the southern hemisphere, so the variation of CO2 mising ratios with the change of seasons is small.

Eli Rabett's long, and perky ears (it is Saturday) leaped as he thought, what would happen if we plotted the difference between the CO2 maxima (before summer warming and greening) and the minima. Would this not be a marker of how much EXTRA CO2 is being absorbed by the biosphere? So ignoring the calls of his loved ones to, well do what loved ones do, such is the call of science, he did for Barrow

and for Mauna Loa
Apologies for these not being on the same scales, but wth, the point is that we DO observe a small increase in the difference between the maximum and minimum observed CO2 during the year.

In the Mauna Loa (MLO) record, while the mixing ratio was going from ~315 ppm in 1958 to ~380 today, the seasonal difference increased about 1 ppm, from about 5 ppm to 6. In the shorter Barrow record, the CO2 mixing ratio went from ~333 ppm in 1974 to ~380 ppm today, but the seasonal difference only increased about 3 ppm from ~14 ppm to ~17 ppm.

In percentage terms the ratio of increase in the seasonal difference to the total increase is 1.5% for Mauna Loa and 6.4% at Barrow. So, those are the numbers, and we are left with the question of what they mean. Obviously, I would like to know if this has been considered in the past, but my first cut at it is at least provocative.

It is taken as a given in carbon cycle circles that about half of the anthropically emitted CO2 is taken up by the biosphere and the oceans and the other half has resulted in the observed increase in atmospheric CO2. A favorite denialist claim is that plants will grow bigger, faster better with increased CO2. In some cases it is claimed that this will completely compensate for human emissions.

However, as we have seen here, if this was the case, one would assume that the seasonal differences would be much larger. That leaves us with the following choices:

  • Northern Hemisphere land vegetation accounts for relatively little photosynthesis, and this analysis sets some strong limits on it. This appears to conflict with studies that show a great deal of CO2 is taken up by Northern Hemisphere forests.
  • Photosynthesis in the Northern Hemisphere evergreen forests accounts for most of the photosynthesis and does not depend strongly on temperature and time of year. Well there go the tree rings.
  • There is a balance between increased photosynthesis in the summer and increased CO2 outgassing from the warmer oceans (and decay [added 10/8]). On net today photosynthesis at warmer temperature wins, but remember that vapor pressure increases exponentially with temperature.
All of these have interesting implications for climate change. Anyone out there have more information or other thoughts.

And so to bed:)


Anonymous said...


A few points:
- The tundra in North Alaska (Barrow) is not the most ideal place to search for seasonal differences and plant uptake.
- A much better place is e.g. Schauinsland, which is in the middle of the Black Forest (if my memory is right), Southern Germany. Data and graphs at:
- The trend there shows much more variability spring-autumn (some 20 ppmv difference, with peaks up to 30 ppmv) than Mauna Loa or Barrow. But there the minima-maxima difference decreases from ~20 ppmv to ~15 ppmv.

IMHO, there is little influence from higher CO2 concentrations on seasonal differences. Most of the bulk sink goes into the oceans. For the terrestrial biosphere, there is a tendency to show more growth with higher CO2 levels, but the yearly amount of debris (leaves) which increases CO2 levels in winter and spring will not change much.

Hank Roberts said...

just looking quickly for review articles that might be relevant, thinking primary productivity is what you're after: SCIENCE VOL 281 10 JULY 1998

Globally, NPP reaches maxima in three
distinct latitudinal bands (Fig. 2). The largest
peak ( 1.6 Pg of C per degree of latitude)
near the equator and the secondary peak at
midtemperate latitudes of the Northern Hemi-
sphere are driven primarily by regional max-
ima in terrestrial NPP. The smaller peak at
midtemperate latitudes in the Southern Hemi-
sphere (Fig. 2) results from a belt of enhanced
oceanic productivity corresponding to en-
hanced nutrient availability in the Southern
Subtropical Convergence (43). At mid and
low latitudes, ocean NPP is remarkably uni-
form, consistent with the predominant influ-
ence of large-scale ocean circulation patterns.
Seasonal fluctuations in ocean NPP are
modest globally, even though regional season-
ality can be very important (44).

Hank Roberts said...

EliRabett said...

ankh, thanks for the links, I've downloaded the papers and am looking at them.

Ferdinand, the middle of the black forest is not a great place for measuring baseline CO2. Stuttgart on the east, Strasbourg on the west, and god help you if the wind comes from Basel in the South or Frankfurt in the north. Even given that Schaueninsel is the LEAST contaminated of all the German sites. That does not mean it is NOT contaminated. See

about 2/3 the way down for the rest of the German sites (Waldhof is the most contaminated).

In any case I am trying to get at the net, not the vegetation contribution.

Anonymous said...


If you want to know the net sink from vegetation, you can better look at O2 levels. These are reduced by fossil fuel burning, but increase again with plant uptake. The net difference between CO2 emissions and CO2 levels in air gives the total uptake (ocean dissolving + vegetation growth), while the difference in expected O2 reduction and observed reduction is a measure for vegetation gowth. Bert Bolin showed a graph at the KTH conference in Stockholm which gives a nice overview.

Not completely right, as all vegetation growth is attributed to terrestrial plants, while there is also increased algue growth in the oceans. But as O2 has a limited solubility in water, that doesn't change the overall picture.

Year-to-year variations in CO2 sink (peak-to-peak or minimum-to-minimum) are highly variable, due to local/regional changes in droughts, rain, temperature (ENSO!) and ocean circulation changes. But as the yearly increase is less than 1% of CO2 in air levels (and less than 0.6% for sinks), that has little influence on the general trend.

The yearly emissions (global) and sinks (as deduced from observations at Mauna Loa) are trended here.

Although there is an increasing trend in the sinks, IMHO this can hardly be used as base for any calculation...

Anonymous said...

Sorry made a mistake in my comment on the last graph: the Fa (flow(air) = net flow of CO2 into the air) is the net yearly C increase in air, not the net sink (which is the difference between the two trends).

What can be seen, is the influece of the Pinatubo (lower temp, more sink) and the 1998 El Niño (higher temp, lower sink)...

Anonymous said...

A longer summer growing season might account for the increase in the difference between max and min.

One would expect the effect to be more pronounced in Barrow, Alaska than Hawaii, since the summer growing season is so short in Barrow to begin with and in Hawaii, the season is already relatively long.

Anonymous said...

I suspect that your third choice is probably the most likely reason why the differences between max and min are less than one might expect.

Because the three stations you provided data for are all located on or near the coast, the ocean undoubtedly has a major effect on the local atmospheric CO2 concentration surrounding each station.

And the latitude would effect the magnitude of the CO2 Concentration oscillattion. In Barrow, the winter ice would act as a "cap" on CO2 outgassing, so the difference in the amount of outgassing between winter and summer would undoubedly be larger there than it would be in Mauna Loa.

Actually, even without outgassing of CO2, the mere fact that the air in the region around the stations is constantly being mixed with with air from out over the ocean means that any seasonal swing in CO2 concentration due to inland vegetation is going to be reduced.

EliRabett said...

Hi everyone,

The point is not that the difference between spring and autumn is different in different places, it is that the difference is not growing very much and that the change in the difference is a measure of how the biosphere is mitigating (or not) the increase in greenhouse gas emissions.

I suspect that any increase in net production of vegetation is compensated by increased emissions from warmer water and decay.

Hank Roberts said...

Another tidbit from a bit of idle Google, found here:

Abstract: The North Pacific subtropical gyre (NPSG), once considered to be a biological desert due to low primary production (PP) and its associated variability, has been found more productive and variable than previously thought. .... Over the last two decades, PP, based on in situ 14C measurements, has increased by approximately 50 %. ....

-- hank roberts

Hank Roberts said...

and another:
-- the html version of the file *which was not found

Solar variability, dimethyl sulphide, clouds,
and climate
S. H. Larsen
C-Research, Lincoln, New Zealand
Received 7 July 2004; revised 22 December 2004; accepted 3 January 2005; published 19 February 2005.
It is proposed that Earth’s climate may be modulated, in part, by changes in the flux
of ultraviolet/blue light into the oceans. This occurs, at a range of timescales, through
solar variability and from damage to the ozone layer. A conceptual model is presented
where, through a number of synergistic processes and positive feedbacks, changes in
the ultraviolet/blue flux alter the dimethyl sulphide flux to the atmosphere, and in turn the
number of cloud condensation nuclei, cloud albedo, and thus sea surface temperature.
The greatest effects are expected in the oligotrophic subtropical oceans, under the Hadley
circulation, in summer.

And we're still getting the biggest ozone holes year after year ....

Hank Roberts said...

and, um,

Three-dimensional chemical model simulations of the ozone layer: 1979-2015
Quarterly Journal of the Royal Meteorological Society, Volume 126, Number 565, April 2000 Part B, pp. 1533-1556(24)

.... The results for 1979-80 and 1994-95 are generally in good agreement with observations, indicating in the latter case a deep Antarctic ozone hole and some Arctic ozone loss. For the 1979 simulation only a very shallow ozone hole was simulated, in agreement with observations. In about the year 2005, the Antarctic ozone hole reaches its maximum size and globally averaged ozone reaches its minimum, depending on the month. Tropical ozone continues to decrease until about 2010. Results in the Arctic are dominated by interannual variability, but minimum ozone may not be attained until the year 2010. The results suggest that the increase in GHGs is delaying the onset of ozone recovery. Relative to 1980 conditions, the model changes in ozone result in small predicted increases in surface ultraviolet radiation in the Arctic and mid-latitude summer but large increases in the tropics and in the Antarctic summer.

Hank Roberts said...

The East China Sea (ECS) is one of the largest continental shelves in the world; however, the role that biota plays in the carbon fluxes of this shelf ecosystem is still obscure.
.... two cruises with stations covering almost the entire shelf were conducted during the high productivity and high river flow season of the ECS in June (the early summer) and August (the middle summer) 2003. Results showed that biological activity was significantly higher in the early summer. To flourish in the early summer, plankton need a significant fluvial input of dissolved inorganic nutrients and organic matter from the Chinese coast, especially from the Changjiang (aka Yangtze River), might be one of the main driving forces. Further analysis showed that most planktonic community respiration (PCR) could be attributed to phytoplankton and bacterioplankton, which accounted for over 96% of the total planktonic biomass (in carbon units) in summer. This might partially explain why mean PCR was higher in June (∼114 mg C m−3 d−1), with higher phytoplankton biomass, than in August (∼40 mg m−3 d−1). The ratio of integrated primary production to PCR (i.e., the P/R ratio) was, however, less than 1, with a mean ± SD value of 0.35 ± 0.41 for all the pooled data. This indicates a significant amount of organic carbon has been regenerated through planktonic activity in the water column. The sea-air difference in fCO2, however, changed from a mean value of −64.5 ± 61.3 ppm in June to 10.0 ± 37.5 ppm in August.

To explain the contradictory results between PCR and fCO2, we suggest that the dissolved inorganic carbon regenerated through planktonic respiration could be stored in the subsurface layer and may affect the fCO2 in the surface water, which is what controls the shelf sea either as an atmospheric CO2 sink or as a source, depending on the prevailing physical forces.

These results also suggest that the controversy between atmospheric CO2 sink or source in the ECS shelf needs further exploration.