Thanks for explaining. So "natural" is the opposite of "anthropogenic", in
a restricted sense. It includes the effect of anthropogenic climate change,
but not the anthropogenic emissions of CO2. Is that right?
Yes, exactly.
I think this is potentially confusing in the context of CF, which has
to cover a wide range of applications. It is not hard to imagine
people wanting to use natural in the sense of *completely* unaffected
by anthropogenic influence. (Obviously I'm not commenting on the
terminology used in OMIP - I'm sure that's clear in that context.) I
wonder if for CF we could think of something more explicit.
Actually I'm unclear quite what is meant by due_to_natural_component
(in several names). Component of what? Could you explain a bit more?
You are right that this may be confusing. In ocean biogemchemical
modeling, anthropogenic CO2 (or anthropogenic dissolved inorganic carbon
in the ocean) is always defined as due only to the increase in
atmospheric CO2 since the onset of the industrial era. Natural CO2 is
everything else, i.e., referring to the idealized unperturbed natural
state AND its changes due to changes climate. So for ocean
biogeochemical community there is less room for ambiguity. These terms
are also defined in the OMIP-BGC protocols paper (in the CMIP6 special
issue):
http://www.geosci-model-dev-discuss.net/gmd-2016-155/
For others, what would you have in mind? One possibility would be to
change part of the name "*_due_to_natural_component"
"*_for_the_natural_component_and_its_changes_due_to_changing_climate"
but that makes for some awfully long names.
Also, what does sea_water_ph_reported_on_total_scale_due_to_X mean? Is it
perhaps a *change* in pH?
No it is not a change in pH, but the pH itself. I see the problem
though, e.g., with the following 2 full names:
* surface_sea_water_ph_reported_on_total_scale_due_to_natural_component
* sea_water_ph_reported_on_total_scale_due_to_abiotic_component
What about just changing the "due_to" to "for_the"
Jim
For the biogeochemistry in OMIP, we've agreed on using the terms
'abiotic' and 'natural', neither synonyms nor antonyms for our
purposes. The OMIP-BGC simulations will be run with 2 parallel
simulations (or parallel tracers in the same simulation):
* 'natural' means it will be maintained at same the CMIP6
preindustrial CO2 level throughout the simulation, while the
* 'total' simulation will have varying atmospheric CO2, but the same
climate (e.g., forced in the OMIP ocean only run).
The difference between the total and natural carbon tracers in the
two will give us the anthropogenic carbon. The ocean's natural
carbon cycle is considered in OMIP to change with climate change
even though its simulated atmospheric CO2 is held constant.
Regarding 'abiotic', the natural and the total simulation include
both abiotic and biotic processes. To distinguish the two we also
include an abiotic carbon tracer. Furthermore, we use a simplified
abiotic approach to model C-14 in the ocean, e.g., to provide
deep-ocean ventilation ages.
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