Dear Chris, Martin, Roy,
I am sorry to hear that confusion is occurring regarding the carbon flux names in C4MIP. I certainly take Chris's point that it would be very unfortunate if the data contain large errors due to misunderstanding of what the variables should contain. However, I do agree with Martin that to change the units of the names to 'kgC' would not be CF compliant because kgC is not a unit in itself, whereas kg clearly is.
I think Roy is right that we need to try and address any confusion via the standard name itself, rather than the units. I am getting the sense that people aren't really understanding the "expressed_as" syntax, even though its inclusion is specifically to address the difference between kg of C and kg of CO2. I haven't had a lot of time to think about this, but my first reaction would be to suggest changing the "expressed_as" names along the following lines:
surface_downward_mass_flux_of_carbon_dioxide_expressed_as_carbon -> surface_downward_mass_flux_of_carbon_contained_in_carbon_dioxide
(just to give an example). For PMIP we did introduce names such as precipitation_flux_containing_17O, so perhaps a similar approach could work for C4MIP?
I think Daniel Neumann also raised some questions last year about the use of "expressed_as" in relation to aerosol names. I confess to still not having worked my way through the whole of that discussion (ironically because I was so occupied with CMIP names last year), but perhaps this is the right time to have a thorough review. It might lead to a lot of aliases being created, but I would be supportive of doing that if it leads to improved clarity across the board. We could start by addressing the names needed for C4MIP and work through the others in batches. Chris, do you think improving the names would help to address the problem?
Best wishes,
Alison
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Alison Pamment Tel: +44 1235 778065
NCAS/Centre for Environmental Data Archival Email: alison.pamment at stfc.ac.uk
STFC Rutherford Appleton Laboratory
R25, 2.22
Harwell Oxford, Didcot, OX11 0QX, U.K.
From: CF-metadata <cf-metadata-bounces at cgd.ucar.edu> On Behalf Of Lowry, Roy K.
Sent: 31 January 2019 12:34
To: Jones, Chris D <chris.d.jones at metoffice.gov.uk>; cf-metadata at cgd.ucar.edu
Subject: Re: [CF-metadata] CMIP6 Confusion regarding carbon flux units
Dear Chris,
The embedding of semantics in units of measure is something I have fought against for decades, largely because software agent AI algorithms are unlikely to look for them there. Your suggestion is also something that would never get past the guardians of UDUNITS.?
However, I can understand your frustration with vital semantics being buried in the long name. Might a better solution be to include the necessary semantics in the Standard Name? This has been done previously. For example:
surface_upward_mass_flux_of_carbon_dioxide_expressed_as_carbon_due_to_anthropogenic_land_use_or_land_cover_change_excluding_forestry_and_agricultural_products
sinking_mole_flux_of_calcite_expressed_as_carbon_in_sea_water
All in all a search for '%flux%expressed_as_carbon%' turned up 39 hits. There are other examples that include phrases like 'expressed as 13C'.
If you are using Standard Names that do not include the 'expressed_as' clause and no suitable alternatives with the clause exist then I would suggest that you put in a new Standard Name request.
Cheers, Roy.
I have now retired but will continue to be active through an Emeritus Fellowship using this e-mail address.
________________________________________
From: CF-metadata <mailto:cf-metadata-bounces at cgd.ucar.edu> on behalf of Jones, Chris D <mailto:chris.d.jones at metoffice.gov.uk>
Sent: 31 January 2019 09:38
To: mailto:cf-metadata at cgd.ucar.edu
Subject: [CF-metadata] CMIP6 Confusion regarding carbon flux units
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Dear Martin, dear All,
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it is emerging that groups are making errors in implementing the carbon cycle data requests - especially regarding the units of carbon fluxes.
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The issue is confusion over whether to report kg of CARBON or kg of CO2.
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The intended correct answer is buried deep within the long name, where fluxes are described as, ".. flux of CO2 expressed as carbon .". But unless you know where to look this is rather hidden and is resulting in groups mixing units of carbon and CO2 across variables.
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So this is a request - actually a plea - that we revisit the decision to include the quantity in the units definition. I have heard the arguments that "kg C" is not an SI unit and we just need to explain it in the long name - but this is really not working and is causing real confusion and errors.
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So PLEASE, PLEASE, can we re-define the labels for carbon fluxes and stores in terms of "kgC m-2 s-1" etc. ?
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There has been such a massive effort to both define and implement this data request it would be a huge shame if substantial errors came in at the last minute - this small change will prevent that.
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thanks,
Chris
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--
Dr Chris Jones
Head, Earth System and Mitigation Science Team
Met Office Hadley Centre, FitzRoy Road, Exeter, EX1 3PB, U.K.
Tel: +44 (0)1392 884514? Fax: +44 (0)1392 885681
E-mail: mailto:chris.d.jones at metoffice.gov.uk? http://www.metoffice.gov.uk/
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Received on Thu Jan 31 2019 - 06:07:26 GMT
