Understanding region emission cap in global model

[lppnog]

Dear all,

I am trying to understand an annual emission cap applied to one region within TIAM. There is a global UC for emissions and a cap only for one region, they are modelled similarly.

It is a COMPRD UC, but the resulting values for TOT* (Var_FOut, Var_comnet, Var_comprd) do not really match the input values. Moreover, the sum of Var_FOut for these TOT* commodities would match the emission account if I sum up the Var_FOut of sectoral emission commodities (given that all are declared in the COMAGG table) in the reference scenario, without the emission cap. When I add the emission cap, the accounting methods do not match anymore and I am struggling a bit to understand why, so I am posting here (see attached snapshot of the UC)


Any insight is welcome! Thank you!

[Antti-L]

Interesting question, but as the model is not available to me, it is a bit difficult to see the full picture.  You say it is a TIAM model, but I have not seen in any TIAM version those processes TU_TOTN2O_GLB*, TU_TOTCH4_GLB* that appear in your user constraint.

It is a COMPRD UC,

As far as I can see, it is not a pure COMPRD UC, but in addition to summing the VAR_COMPRDs for TOTCO2, TOTCH4 and TOTN2O multiplied by some CO2-eq. coefficients, you also subtract the VAR_ACTs of various TU_* processes, multiplied also by the corresponding CO2-eq. coefficients. The amount you are limiting is thus not the total commodity production of GHGs, but that production subtracted by the activities of some TU_* processes. I assume that these TU_* processes are some trade processes for GHGs. The role of the TU_NONCO2* process(es) is particularly interesting in your equation...

but the resulting values for TOT* (Var_FOut, Var_comnet, Var_comprd) do not really match the input values.

If you mean that the sum of the VAR_COMPRDs for TOTCO2, TOTCH4 and TOTN2O (multiplied by the CO2-eq. coefficients) does not match the UC_RHSTS values, that is understandable, as you are not actually limiting that sum. It seems clear that the sum could be both larger or smaller than the UC_RHSTS input values. The same applies to the sum of Var_Fout.

When I add the emission cap, the accounting methods do not match anymore.

I am not sure what you mean by "the accounting methods do not match anymore". Can you demonstrate that by presenting the VEDA-BE results where the non-matching accounting methods can be seen? It would also help if you would show all the levels of the variables involved in the equation (VAR_COMPRDs for TOTCO2, TOTCH4 and TOTN2O, and VAR_ACTs for all the TU_* processes involved), in the given region (MDG).

[lppnog]

Interesting question, but as the model is not available to me, it is a bit difficult to see the full picture.  You say it is a TIAM model, but I have not seen in any TIAM version those processes TU_TOTN2O_GLB*, TU_TOTCH4_GLB* that appear in your user constraint.

It is a COMPRD UC,

As far as I can see, it is not a pure COMPRD UC, but in addition to summing the VAR_COMPRDs for TOTCO2, TOTCH4 and TOTN2O multiplied by some CO2-eq. coefficients, you also subtract the VAR_ACTs of various TU_* processes, multiplied also by the corresponding CO2-eq. coefficients. The amount you are limiting is thus not the total commodity production of GHGs, but that production subtracted by the activities of some TU_* processes. I assume that these TU_* processes are some trade processes for GHGs. The role of the TU_NONCO2* process(es) is particularly interesting in your equation...

but the resulting values for TOT* (Var_FOut, Var_comnet, Var_comprd) do not really match the input values.

If you mean that the sum of the VAR_COMPRDs for TOTCO2, TOTCH4 and TOTN2O (multiplied by the CO2-eq. coefficients) does not match the UC_RHSTS values, that is understandable, as you are not actually limiting that sum. It seems clear that the sum could be both larger or smaller than the UC_RHSTS input values. The same applies to the sum of Var_Fout.

When I add the emission cap, the accounting methods do not match anymore.

I am not sure what you mean by "the accounting methods do not match anymore". Can you demonstrate that by presenting the VEDA-BE results where the non-matching accounting methods can be seen? It would also help if you would show all the levels of the variables involved in the equation (VAR_COMPRDs for TOTCO2, TOTCH4 and TOTN2O, and VAR_ACTs for all the TU_* processes involved), in the given region (MDG).

Hi Antti,
thanks for the explanations. If it helps, I have attached a file to help following my reasoning.

So, what I get from this is: 
- the Var_FOut emissions from TOT* emissions commodities correspond to the VAR_Comnet (and not Var_FOut!) of sector emission commodities as included in the aggregation table. 
- If my accounting is correct (see estimates on row 64 in 'account' tab), then the UC is indeed ok, as the result is lower than the UP value...

Best regards,

[Antti-L]

Yes, the sectoral emissions aggregated by COM_AGG are the NET emissions (VAR_COMNET), not gross emissions. Otherwise they would give very incorrect values for the total GHG emissions.

the Var_FOut emissions from TOT* emissions commodities correspond to the VAR_Comnet (and not Var_FOut!) of sector emission commodities as included in the aggregation table.

This is not quite correct. The Var_FOut of the TOT* emissions include also any process outputs of them in the model. For example, the outputs of TOT* emissions from the TU_* processes are included. Thus, for example the total Var_FOut of TOTCO2 emissions consist of the sum of the sectoral net emissions (because of the aggregation) plus the sum of any process outputs of TOTCO2.  However, again, there may be some processes consuming TOTCO2 (for example, CO2 storage and afforestation processes in TIAM), and so if you want to put a limit on the amount of emissions released into the atmosphere, you should normally define the constraint on the NET emissions (VAR_COMNET), and not on the gross emissions (VAR_COMPRD).

[lppnog]

Dear Antti,

you are absolutely correct on your remarks, I forgot to mention the subtracting of TU* processes in my previous comment. Thanks for your help and suggestions!

Best Regards,