DOI: 10.5061/dryad.83bk3jb1h
title: Canada’s extreme wildfires dominate the decline in global land carbon sinks in 2023

description: Terrestrial land carbon sinks are strongly influenced by climate extremes,
 and 2023 is the warmest year on record, accompanied by an El Niño event,
 extreme wildfires, and extreme precipitation and drought, but their impact
 on global land sinks in 2023 remains unclear. Here, we used the Global
 Carbon Assimilation System, version 2, to estimate recent global land
 sinks by assimilating the OCO-2 ACOS v11.1 XCO2 retrievals. We estimate
 the global land sink to be -1.63 ± 0.52 PgC/yr in 2023. Compared to
 2017-2022, it decreases by 0.59 PgC/yr, in which net ecosystem exchange
 decreases by only 0.14 PgC/yr, but wildfire emissions increase
 significantly by 0.45 PgC/yr, mainly in Canada. Our findings suggest that
 extreme wildfires are an important threat to land sinks under global
 warming.
description: We generate this dataset using the Global Carbon Assimilation
 System, version 2 (GCASv2) by assimilating OCO-2 ACOS v11.1
 XCO<sub>2</sub> retrievals. GCAS v2 was developed to estimate
 gridded surface carbon fluxes by assimilating primarily satellite
 XCO<sub>2</sub> retrievals, which consists of the Model for
 Ozone and Related Chemical Tracers, version 4 (MOZART-4) and the ensemble
 square root filter (EnSRF). It has good performance in assimilating GOSAT
 and OCO-2 XCO<sub>2</sub> retrievals, revealing the response
 of terrestrial ecosystems to extreme climate events, and has participated
 in the inversion of the Global Carbon Budget 2023. For
 this dataset, GCASv2 was run from 6 September 2014 to 6 January 2024 with
 a DA window of 1 week. Only the terrestrial net ecosystem exchange (NEE)
 and the atmosphere-ocean carbon exchange (OCN) were optimized, and the
 carbon emissions from fossil fuels and cement (FFC) and from wildfires
 were prescribed. Usually, the choice of a priori NEE has an important
 impact on the inversion of terrestrial carbon sinks, thus we used the
 simulations of two terrestrial ecosystem models (i.e., BEPS and CASA) as a
 priori NEE. In addition, there are large discrepancies among different
 wildfire CO<sub>2</sub> emission datasets, indicating that the
 estimation of wildfire emissions is also subject to considerable
 uncertainty. To reduce the impact of such uncertainty on our inversion,
 two wildfire emission datasets (i.e., GFED 4.1s and GFAS) were adopted.
 Therefore, we performed four inversion experiments (Exp_BEPS&GFED,
 Exp_BEPS&GFAS, Exp_CASA&GFED, and Exp_CASA&GFAS)
 with different prior NEEs and wildfire emissions to obtain a more robust
 estimate of the NBE (=NEE + wildfires).
description: # Canada’s extreme wildfires dominate the decline in global land carbon
 sinks in 2023
 [https://doi.org/10.5061/dryad.83bk3jb1h](https://doi.org/10.5061/dryad.83bk3jb1h) ## Description of the data and file structure There are 6 zip files in this dataset, including (1) monthly and annual prior and posterior NEE and OCN fluxes, and prescribed wildfire and fossil fuels and cement emissions in a global spatial resolution of 1°×1° from the 4 experiments (Global prior and posterior fluxes at 1deg resolution.zip); (2) globally (Global_Carbon_Budget.zip), latitudinally (Lat_Zones.zip), and regionally (Transcom_regions.zip, Canada.zip) aggregated annual fluxes of NEE, wildfire emissions, and NBE from the 4 experiments; (3) adjusted fluxes for Canada and different latitudinal zones using different thresholds because of the compensating effect between NEE and wildfire emissions (Adjusted.zip). Details about these zip files are as follows: **1) Global prior and posterior fluxes at 1deg resolution.zip** There are 4 files in the netcdf format from 4 inversion experiments, each with the same variables, including monthly (unit: gC/m2/month) and annual (unit: gC/m2/year) NEE a priori and a posteriori fluxes, atmospheric-ocean a priori and a posteriori carbon fluxes, and prescribed fossil fuel and cement carbon emissions and wildfire emissions. For monthly fluxes, they span from Sep, 2014 to Jan, 2024, and for annual fluxes, they span from 2014 to 2024. **2) Global_Carbon_Budget.zip** There are 5 txt files in this zip file, which are the aggregated global annual fluxes in PgC/yr for the a posteriori NEE and atmospheric-ocean carbon fluxes, and prescribed wildfire and fossil fuel emissions from the four experiments and averages of the four experiments. **3) Lat_Zones.zip** There are 5 txt files in this zip file, which are the aggregated NEE, wildfire emissions, and NBE (=NEE + wildfire emissions) from the four experiments and averages of the four experiments in different latitudinal bands, including the northern mid to high latitudes (≥30° N, NL), the tropical latitudes (30° S–30° N, TL), and the southern mid latitudes (≤30° S, SL). **4) Transcom_regions.zip** The same as Lat_Zones.zip, but for different TRANSCOM regions. **5)  Canada.zip** The same as Lat_Zones.zip, but for Canada. **6) Adjusted.zip** There are 8 txt files in this zip file, including adjusted NEE and wildfire emissions for Canada and different latitudinal bands (i.e., NL, TL, and SL) using different thresholds.  Only averages of the four experiments are provided.