09:00 〜 10:30
[ACG35-P03] Uncertainties in historical fossil fuel emissions will influence tracking of NDCs and Global Stocktake
キーワード：Fossil fuel emission, Inverse modelling, Global stocktake
Fossil fuel emissions are taken as accurate knowledge in emission/removal estimation of CO2 in the top-down modelling system. However, large uncertainties in fossil fuel emission distributions are likely to be present, particularly in the decade of 2000s, which is when many countries set their baselines for reporting Nationally Determined Contributions (NDCs) and policies toward achieve net-zero emission goals by global stocktake.
We used fossil fuel emissions (CO2ff): the gridded fossil fuel emission dataset (GridFED; Jones et al., 2021) for inverse modelling experiments using JAMSTEC's MIROC4-ACTM tracer transport model. Three cases based on GCP-2022 are used: 1) GridFEDmean: the control emission used in GCP2022 budget and inversions, 2) GridFEDlow: lower bound of GridFED emission inventory, and 3) GridFEDhigh: upper bound of GridFED emission inventory. In addition to the control/mean emissions provided for GCP budget analysis, GridFED also provides upper and lower bounds of emissions at every 0.1 x 0.1 degree grids. These ranges are applied for preparing GridFEDhigh and GridFEDlow emission cases, respectively (Figure, left column).
Our analysis show that the GridFED emissions increased rapidly during 2002-2010 for all the cases, mean, upper and lower bounds. The increase rate is also moderated in the GridFEDlow case compared to the GridFEDhigh case. Clear manifestations of different fossil fuel emissions are seen on the estimated land CO2 fluxes (Figure, middle column), while the ocean CO2 fluxes (Figure, right column) remained undisturbed, by the inversions. This is because the fossil fuel emissions mainly occur on the land, and the inversions estimate residual sinks on land and into the ocean. The inversions using two different CO2 data uncertainties produced near identical flux estimations at the global land and ocean partitions when the same set of prior fluxes are used.
When the fossil fuel emissions increased at the fastest rate during 2002-2010, the inversion estimated land sink also increased. Such emission and sink link was highlighted for the East Asia region by jointly analysing CO2 and CH4 inversion results (Saeki and Patra, 2017). However, no detailed analysis was performed due to the lack of information on fossil fuel emission uncertainty. The upper and lower bounds in gridded fossil fuel emissions are now available in GridFED. In the northern extratropical latitudes (north of 30N), large and persistent biases in fossil fuel emissions are seen and thus in the compensating residual land sinks. For the northern tropical latitudes, a difference in fossil fuel emissions increase rate is seen and a similarly compensating land flux change rates. No significant fossil fuel emission and residual flux estimation are seen for the southern tropics and southern extratropics.
This analysis allows us to conclude that the global total land sink increase in the period of about 2000-2010 mainly originated in the northern extratropical latitudes, which is most prominently seen for the period 2002-2008 (top row, middle column). This fast increase in land sink in the northern extratropical latitudes is too fast to be true, and has most likely arisen from a bias in Chinese fossil fuel emission increase trend. More discussions are required for resolving the uncertainties in fossil fuel emission uncertainties in the 2000s, or revise the baselines for NDCs to a period when the emissions are better estimated, e.g., the early 2010s (the satellite CO2 era).
We used fossil fuel emissions (CO2ff): the gridded fossil fuel emission dataset (GridFED; Jones et al., 2021) for inverse modelling experiments using JAMSTEC's MIROC4-ACTM tracer transport model. Three cases based on GCP-2022 are used: 1) GridFEDmean: the control emission used in GCP2022 budget and inversions, 2) GridFEDlow: lower bound of GridFED emission inventory, and 3) GridFEDhigh: upper bound of GridFED emission inventory. In addition to the control/mean emissions provided for GCP budget analysis, GridFED also provides upper and lower bounds of emissions at every 0.1 x 0.1 degree grids. These ranges are applied for preparing GridFEDhigh and GridFEDlow emission cases, respectively (Figure, left column).
Our analysis show that the GridFED emissions increased rapidly during 2002-2010 for all the cases, mean, upper and lower bounds. The increase rate is also moderated in the GridFEDlow case compared to the GridFEDhigh case. Clear manifestations of different fossil fuel emissions are seen on the estimated land CO2 fluxes (Figure, middle column), while the ocean CO2 fluxes (Figure, right column) remained undisturbed, by the inversions. This is because the fossil fuel emissions mainly occur on the land, and the inversions estimate residual sinks on land and into the ocean. The inversions using two different CO2 data uncertainties produced near identical flux estimations at the global land and ocean partitions when the same set of prior fluxes are used.
When the fossil fuel emissions increased at the fastest rate during 2002-2010, the inversion estimated land sink also increased. Such emission and sink link was highlighted for the East Asia region by jointly analysing CO2 and CH4 inversion results (Saeki and Patra, 2017). However, no detailed analysis was performed due to the lack of information on fossil fuel emission uncertainty. The upper and lower bounds in gridded fossil fuel emissions are now available in GridFED. In the northern extratropical latitudes (north of 30N), large and persistent biases in fossil fuel emissions are seen and thus in the compensating residual land sinks. For the northern tropical latitudes, a difference in fossil fuel emissions increase rate is seen and a similarly compensating land flux change rates. No significant fossil fuel emission and residual flux estimation are seen for the southern tropics and southern extratropics.
This analysis allows us to conclude that the global total land sink increase in the period of about 2000-2010 mainly originated in the northern extratropical latitudes, which is most prominently seen for the period 2002-2008 (top row, middle column). This fast increase in land sink in the northern extratropical latitudes is too fast to be true, and has most likely arisen from a bias in Chinese fossil fuel emission increase trend. More discussions are required for resolving the uncertainties in fossil fuel emission uncertainties in the 2000s, or revise the baselines for NDCs to a period when the emissions are better estimated, e.g., the early 2010s (the satellite CO2 era).