Ontology: Include "CO2 equivalents" and "global warming potential"

[l-emele]

Description of the issue

We already included the concepts _emission_, _greenhouse gas emission_, _carbon dioxide_ and so on. In this context we need also _CO2 equivalents_ and _global warming potential_.

Ideas of solution

If you already have ideas for the solution describe them here

Workflow checklist

• [ ] I discussed the issue with someone else than me before working on a solution
• [ ] I already read the latest version of the workflow for this repository
• [ ] The goal of this ontology is clear to me

I am aware that

• [ ] every entry in the ontology should have a definition
• [ ] classes should arise from concepts rather than from words

[han-f]

Could we start from this thought: _The CO2 equivalent is an indicator which shows how strongly a certain greenhouse gas acts in comparison to carbon dioxide (CO2)_ ?

[l-emele]

Good start. What about _metric_ instead of _indicator_? https://en.wiktionary.org/wiki/metric#Noun

I like the word _metric_ as it is etymologically related to measurement.

[l-emele]

Actually, Wikipedia has a good definition: _Carbon dioxide equivalency is a quantity that describes, for a given mixture and amount of greenhouse gas, the amount of CO2 that would have the same global warming potential (GWP), when measured over a specified timescale (typically 100 years)._

Do we all agree that CO2 equivalent is a _quantity_?

[l-emele]

The IPCC defines/describes CO2 equivalents as:

The amount of carbon dioxide (CO2) emission that would cause the same integrated radiative forcing or temperature change, over a given time horizon, as an emitted amount of a greenhouse gas (GHG) or a mixture of GHGs. There are a number of ways to compute such equivalent emissions and choose appropriate time horizons. Most typically, the CO2-equivalent emission is obtained by multiplying the emission of a GHG by its global warming potential (GWP) for a 100-year time horizon.

(Glossary of the _2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories_)

[stap-m]

The concept of CO2 equivalent could maybe also be seen as quality: it is a specific property a greenhouse gas inherits, like its mass.

[l-emele]

Isn't the quality of the gas the global warming potential? CO2 equivalents is something that is calculated _using_ / _applying_ the GWP. Additionally, CO2 equivalents can be given not only for a single gas but also for a mix of gases.

In our conversion paper I have the example of 100 Mt CO2, 0.5 Mt CH4 and 0.2 Mt N2O that can be expressed as 167 Mt CO2 equivalents.

[stap-m]

Ok, then GWP would be the quality/property of the substance. CO2 equivalent is rather a mathematical concept, i.e. a factor, to make the GWP of different substances comparable?

[l-emele]

Ok, then GWP would be the quality/property of the substance.

Isn't a quantity? You can e.g. methane has a GWP of 25 (kg/kg). We already have a the (currently undefined and unused) property has_globalwarmingpotential. But we might do it differently. We could delete has_globalwarmingpotential and define instead a class global warming potential. Then we could link with the global warming potential with a has quantity value property (or something similar) to the class greenhouse gas. Then all greenhouse gases would inherit this relation.

CO2 equivalent is rather a mathematical concept, i.e. a factor, to make the GWP of different substances comparable?

Yes, exactly.

[stap-m]

I like the idea of replacing has_globalwarmingpotential and I would like to extend your proposal @l-emele:
One cannot "move" GWP from one substance to another, it is specifically dependent. But a quantity value is a generically dependent continuant. Therefore I still suggest to classify GWP as quality.
But the GWP is measured in CO2 equivalents and the corresponing quantity value would be CO2 equivalent:
A greenhouse gas has quality global warming potential which has quantity value CO2 equivalent for a certain period.
I am somehow still struggeling with understanding the usage of the quantity value class... Does this make sense from an ontological point of view ❔ @OpenEnergyPlatform/oeo-general-expert-formal-ontology

[l-emele]

Shouldn't then all quantity values be specifically dependent? We currently have the quantity values declared net capacity, nameplate capacity, power rating and storage capacity. They are in the same way dependent on objects (here power plants or energy storages) as GWPs are dependent on greenhouse gases.

In my understanding both GWP and CO2 equivalent are quantity values, but with different dimensions. GWP is a dimensionless quantity, CO2 equivalent has the dimension of mass.

[jannahastings]

But the GWP is measured in CO2 equivalents and the corresponing quantity value would be CO2 equivalent:
A greenhouse gas has quality global warming potential which has quantity value CO2 equivalent for a certain period.

On my understanding, quantity values are the outcomes of measurements or calculations and they are _about_ some or other physical entity, which might be a quality. For global warming potential, there is clearly some sort of quality or attribute that is transformed into a quantity value in some (I assume standardised) way. But the way that 'global warming potential' is used, it is usually used together with a number right?

I found on the internet statements of two forms:

1. That (e.g.) 1kg methane has global warming potential 25kg CO2e
2. That nitrous oxide has a GWP 265–298 times that of CO2.

To me, my reading of these assertions is is that global warming potential here is a quantity value and CO2 equivalent is its unit. In (1) this is explicit, while in (2) it is implicit.

[l-emele]

I am currently trying spelling out these concepts and the methological details and differences between them in the conversion paper we are writing for the SzenarienDB project. This paper is due end of June. Maybe we wait with implementing this issue until the paper is finalised. At least from my site is now urgency for this issue, so we have time to find a solution all can agree.

[stap-m]

I think the way UO is used is something along these lines:
There are always four separate things: (1) the entity in reality (some sort of specifically dependent continuant, perhaps, or a process) (2) a number (3) a unit. The entity then has_value some (4) quantity value entity, that has_unit the unit. (And may have a specified value with a data property). The relationship between the quantity value entity (4) and the entity in the world (1) is is_about.

https://github.com/OpenEnergyPlatform/ontology/issues/434#issuecomment-648837549 @jannahastings commented here on the use of the UO (unit ontology). This might be helpful here, too.

[han-f]

The paper @l-emele mentioned has now been published: https://doi.org/10.5281/zenodo.3949691
GWPs are discussed in Section 4.

[l-emele]

Starting again with this issue by looking into what I've written in the mentioned paper:

• Global Warming Potential:

  The Intergovernmental Panel on Climate Change (IPCC) provides a definition of the GWP:

  The Global Warming Potential (GWP) is defined as the time-integrated RF [radiative forcing] due to a pulse emission of a given component, relative to a pulse emission of an equal mass of CO2 [...]. [2, p. 710]
  This means that the GWP is a measure how much additional energy is added to the atmosphere by a specific amount of a greenhouse gas over a time period compared to the effect of the same amount of CO2. Despite its name, the GWP does not measure directly the temperature change (warming) effect. (Footnote: In fact, the IPCC states: Thus, the name 'Global Warming Potential' may be somewhat misleading, and _relative cumulative forcing index_ would be more appropriate. [2, p. 711])

• CO2 equivalent emissions:

  CO2 equivalent emissions [...] can be calculated using the emissions of individual gases and the global warming potentials of these gases.
  A special case are CO2 emissions from biomass combustion. During their lifetime plants extract CO2 from the atmosphere to grow. During the combustion of biomass the same amount of CO2 is emitted that were extracted by the plants before. Thus the CO2 emissions from biomass combustion are usually excluded from CO2 equivalents.

[Vera-IER]

To me, my reading of these assertions is is that global warming potential here is a quantity value and CO2 equivalent is its unit.

I agree. If we take the label CO2 equivalent emission , we could use emission as parent class. Using these as parent classes the definitions can be rewritten to:

_Global warming potential is a quantitiy value that is defined as the time-integrated radiative forcing due to a pulse emission of a given component, relative to a pulse emission of an equal mass of CO2._
_CO2 equivalent emission is a emission that can be calculated using the emissions of individual gases and the global warming potentials of these gases._

[l-emele]

But emission is a process and a process cannot be calculated. But values describing that process can be calculated, so CO2 equivalent emission might be more a subclass of quantity. Or maybe CO2 equivalent is more something like a unit?

[Vera-IER]

Okay I can see that. I think defining CO equivalent emission as a quantity or CO2 equivalent as a unit are both possible from the definition point of view. I don't know if it is possibible to combine 2 different units in an ontology. If we define it as a unit, we would need to use this "index" unit and additionally a mass unit (e.g. Mt) to describe data.

[l-emele]

We have a class ratio as subclass of dimensionless unit that can be used to define the GWP:
_Global warming potential is a ratio that measures the the time-integrated radiative forcing due to a pulse emission of a given component, relative to a pulse emission of an equal mass of CO2._
So this definition proposal is basically the same as the one from @Vera-IER except for a different parent class. I don't know which superclass is more appropriate here. What do @OpenEnergyPlatform/oeo-general-expert-formal-ontology suggest?

Regarding CO2 equivalents, what about:
_CO2 equivalent emission quantity is a quantity value that describes the combined effect of all emitted greenhouse gases. It can be calculated using the emission quantity values of individual gases and the global warming potentials of these gases._

As this definition proposal uses emission quantity value we should define that, too:
_An emission quantity value is the output of an emission process. It can be calculated using the emission factor of that emission process._

[sfluegel05]

I think global warming potential should be neither be a ratio nor a quantity value. We certainly need instances of both classes to describe a global warming potential, but the global warming potential itself looks to me like a concept which specifically depends on a gas (portion of matter and has state gaseous). So it should probably be a quality which then is related to a quantity value.

CO2 equivalent emission quantity depends on a process (an emission), so it could be a process attribute.

I am not sure what is meant with emission quantity value. Does this belong to an emission or an individual gas?

[l-emele]

Thanks for that feedback. I try to condense what we already discussed and some further thoughts in a top-down structure:

• Emission is a process that has output some portion of matter which can be quantified via its mass. That should be already in the OEO. The emission process needs an process attribute which could be an emission quantity value with the the following proposed definition (slightly improved compared to above):
  _An emission quantity value is a process attribute that quantifies the output of an emission process. It can be calculated using the emission factor of that emission process._
• The emission factor is also an process attribute but a different one which we already included in the OEO as:
  _An emission factor is a process attribute that quantifies the emissions or removals of a gas per unit activity._
• Greenhouse gas emission is a special kind of emission process which has output some greenhouse gas:
  _A greenhouse gas emission is an emission that releases a greenhouse gas._
  Hence its process attribute could be an greenhouse gas emission quantity value:
  _A greenhouse gas emission quantity value is an emission quantity value that quantifies the output of an greenhouse gas emission process._
• Then we could have subclasses of greenhouse gas emission like CO2 emission, methane emission and so on for the individual greenhouse gas emissions.
• A lot of greenhouse gas emission process have a bunch of gases as output, e.g. a power plant emits next to CO2 also a small amount of methane (CH4) and nitrous oxide (N2O). These gases have different contribution to global warming than CO2.
• Global warming potential is the common metric to make the effects of the different greenhouse gases comparable. These are properties of the specific gases as pointed out by @sfluegel05. We already defined a property has global warming potential as:
  _A relation between a portion of matter and the global warming potential it has._
  We can use that property to connects the greenhouse gases to global warming potential.
• The CO2 equivalent emission quantity is a special kind of emission process attribute that quantifies the combined effect of all emitted greenhouse gases by giving an equivalent amount (mass) of CO2 which would have the same effect on the climate. So it does not give the _actual_ output of that process but only an output that has an _equivalent effect_ and that it causing some headache how to classify properly. Maybe it is an subclass of greenhouse gas emission quantity value, maybe it is a bit different concept?

[sfluegel05]

Thanks for this overview. I am not sure if we really need emission quantity value and its subclasses. As it just quantifies the output of an emission process, we could instead use has output to connect outputs to an emission (like we do for other processes).
I would prefer to make CO2 equivalent emission quantity a subclass of greenhouse gas emission quantity value (if we include it) because it it still a quantification of the output, just measured differently.

[sfluegel05]

We (@l-emele and me) came to the following conclusion:

• for global warming potential we can use the already existing relation has global warming potential which relates greenhouse gasses to quantity values
  We want to add the following classes:
• emission value: _An emission value is a process attribute that quantifies the output of an emission process. It can be calculated using the emission factor of that emission process._
• greenhouse gas emission value: _A greenhouse gas emission value is an emission value that quantifies the output of a greenhouse gas emission process._
• carbon dioxide equivalent quantity (alternative term: CO2 equivalent quantity): _A carbon dioxide equivalent quantity is a greenhouse gas emission value that quantifies the combined effect of all emitted greenhouse gases by giving an equivalent amount of CO2 which would have the same effect on the climate._

@stap-m Do you agree with this?

[stap-m]

I do. Nice work.

If do not define GWP as an own class, we need to specify def of has global warming potential.
Which currently is: _A relation between a portion of matter and the global warming potential it has._

We could use the proposal by @l-emele, see above, and just add it:
_A relation between a portion of matter and the global warming potential it has. The global warming potential is a ratio that measures the the time-integrated radiative forcing due to a pulse emission of a given component, relative to a pulse emission of an equal mass of CO2._

[l-emele]

Hm, maybe in the end we were now too quick with the implementation.

We could use the proposal by @l-emele, see above, and just add it:
A relation between a portion of matter and the global warming potential it has. The global warming potential is a ratio that measures the the time-integrated radiative forcing due to a pulse emission of a given component, relative to a pulse emission of an equal mass of CO2.

This solution now mixes a relation and a definition of a class which I am a bit unhappy with. Further, we have this relation but it is still not applied, not even for the most obvious class greenhouse gas.

[stap-m]

@l-emele would you prefer an additional class global warming potential? We have to define it anywhere...
@jannahastings do you know a good way how to solve this?

I agree that we should add the relation to greenhouse gas and all subclasses should inherit it.

[l-emele]

@l-emele would you prefer an additional class global warming potential? We have to define it anywhere...

Yes, the addition of a class global warming potential was the purpose of this issue anyway. I still like the definition above:
_Global warming potential is a ratio that measures the the time-integrated radiative forcing due to a pulse emission of a given component, relative to a pulse emission of an equal mass of CO2._
Even subclasses are possible as there are different kinds of global warming potentials differentiated by different integration time intervalls (typically 20, 100 and 500 years).

To me, 'greenhouse gas' has_global_warming_potential some 'global warming potential' makes totally sense.

Shall we re-open this issue?

[stap-m]

I agree. The definition suggests that global warming potential is a quantity value, which seems fine to me.

[stap-m]

Even subclasses are possible as there are different kinds of global warming potentials differentiated by different integration time intervalls (typically 20, 100 and 500 years).

Subclasses or individuals?

[l-emele]

I agree. The definition suggests that global warming potential is a quantity value, which seems fine to me.

Yes, right, it is a quantity value with the unit ratio, so it should be: _Global warming potential is a quantity value that measures the the time-integrated radiative forcing due to a pulse emission of a given component, relative to a pulse emission of an equal mass of CO2._
It additionally should get the relation: has_unit some ratio.

Even subclasses are possible as there are different kinds of global warming potentials differentiated by different integration time intervalls (typically 20, 100 and 500 years).

Subclasses or individuals?

These would be subclasses. The individuals would be the GWPs for specific gases, but not the GWPs in general.

[l-emele]

Can I interpret your thumbs up that we have a consensus and I can implement this class?

[stap-m]

Yep, from my side.

[l-emele]

Okay, I started implementing.

While doing this, I discovered that the relation has global warming potential has the domain 'greenhouse effect disposition' and the range 'quantity value' and ('has unit' some ratio). Is does this still makes sense? The definition is: _A relation between a portion of matter and the global warming potential it has._ Following this definition, shouldn't be the domain be portion of matter and the relation be global warming potential.

I would argue further that the definition should be updated to _A relation between a greenhouse gas and the global warming potential it has._ as _A greenhouse gas is a portion of matter that has the disposition to contribute to the greenhouse effect._ which has the axiom 'portion of matter' and ('has disposition' some 'greenhouse effect disposition').

@sfluegel05 or @jannahastings : What do you think?

[jannahastings]

I agree.