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But on the Papers: not being a scientist I can only comment on this in general. The whole Paper seems to be based on the premise that the seasonal fluctuations in CO2 levels measured all over the world are linked to photosynthesis. Yes, there is that link, but is there any peer-reviewed paper quantifying exactly how much! Anyone?
We do know that CO2 uptake and emissions are not attributable to one single source, there are other factors as well. Agriculture for one: soil respiration might fluctuate with seasonal (traditional) soil tillage. Oceans have an uptake and respiration cycle as well, which possibly could be seasonal (temperature) driven?
AFAIK we can not yet quantify the effect of photosynthesis as a percentage of the whole uptake and if that is correct, the Papers are indeed based on an assumption, not on scientific "gospel".
I'm sure there are more scientific arguments "out there" and I'm equally sure they will be learning experiences!
https://tamino.wordpress.com/2012/06/01/annual-cycle-of-co2/ and it seems o "not support" the Curran Papers.
@ PatH: Thanks very much for that contribution! Glad to have suggested a useful link
Abstract:
Accurate assessment of anthropogenic carbon dioxide (CO2 ) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere is important to better understand the global carbon cycle, support the climate policy process, and project 5 future climate change. Present-day analysis requires the combination of a range of data, algorithms, statistics and model estimates and their interpretation by a broad scientific community. Here we describe datasets and a methodology developed by the global carbon cycle science community to quantify all major components of the global carbon budget, including their uncertainties
A comment detailed this as follows: >> Taken the year 2011: human emissions were 10.4±1.0 PgC. Growth in the atmosphere was 3.6±0.2 PgC (only 35% from the emissions) Oceans got 2.7±0.5 PgC (26%) and land 4,1±0.9 PgC (39%). <<
Is this Paper, these datasets in any way reflected in the Curran Papers under discussion?
http://www.earth-syst-sci-data-discuss.net/5/1107/2012/essdd-5-1107-2012.pdf
(Perhaps the issue is with the presentation of the data in the Curran Papers, less than with the premise??)
>> Trees also reduce their photosynthesis due to ozone. That makes it a double whammy for climate change — as a greenhouse gas, ozone directly causes global warming; but it also does so indirectly, by reducing the amount of CO2 that trees take up. <<
http://e360.yale.edu/feature/ground_level_ozone_harming_plants_humans/3044/
Take a look at the Global Carbon Project, a detailed annual study done by many specialist scholars. They bring together inventories, observations and models. They conclude that the land uptake, although very variable, shows no sign of any recent decrease. Here are a couple of slides from that presentation.
I would have to regard this study as much more reliable--using as it does many different lines of evidence--than the Curran & Curran work.
I do think that the land sink needs to be watched closely and, indeed, I have written about how carbon-cycle feedbacks may hold some nasty surprises for us over decades to come. I just do not think that major changes have been observed yet.