## 4 Results
### Attribution of Detected High XCO\({}_{2}\) Units by Surface Extremes
Their land over types, period, grids number (NUM), location, dXCO\({}_{2}\), Z score, and difference between monthly data and its normal value over significant different period about surface skin temperature (\(\Delta\)Temp), self-calibrating Palmer drought severity index (scPDSI) (negative for drought and vice versa), burned area (\(\Delta\)BA) and gross primary production (\(\Delta\)GFP) during the main detected period over these units. Positive values indicate increasing values during the extreme event. Bold items indicate likely contribution to the atmospheric XCO\({}_{2}\) increase, because they represent forcing that likely increases CO\({}_{2}\) flux to the atmosphere. Figure 4: Monthly data, from 2009 to 2016, of parameters including surface skin temperature (Temperature), scPDSI, BA and GPP over detected high XCO\({}_{2}\) extreme units 1–5. Red line is the observed dataset and the blue line is seasonal mean data over the 3 years, calculated using the observed data. Time within black dashed lines indicates each extreme high XCO\({}_{2}\) unit. Figure 5: Monthly data, from 2009 to 2016, of parameters including surface skin temperature (Temperature), scPDSI, BA and GPP over detected XCO\({}_{2}\) extreme units 6–10. Red line is the observed dataset and the blue line is seasonal mean data over the 8 years, calculated using the observed data. Time within black dashed lines indicates each extreme high XCO\({}_{2}\) unit. We find that abnormal increased temperature (1.22 \(\pm\) 1.60, 1.78 \(\pm\) 0.80 K), moderate/severe drought (\(-\)1.11 \(\pm\) 0.18, \(-\)1.98 \(\pm\) 0.44), increased wildfire (8.77 \(\pm\) 7.82, 57.47 \(\pm\) 108.69 km\({}^{2}\)/grid), increased CO\({}_{2}\) release, and reduced GPP (\(-\)5.85 \(\pm\) 4.94, \(-\)11.50 \(\pm\) 5.31 gC/m\({}^{2}\)), emerge together over the time and space of units Ex-1 and Ex-8. All of them could contribute to the abnormal XCO\({}_{2}\). In 2016 in the SH, XCO\({}_{2}\) anomalies in Ex-2, Ex-3 and Ex-4 resulted from a combination of influences of abnormal increased temperature (1.56 to 1.93 K), severe drought (\(-\)1.31 to \(-\)2.10), reduced GPP (\(-\)5.99 to \(-\)26.66 gC/m\({}^{2}\)). XCO\({}_{2}\) anomaly over Ex-6 could be explained by flooding indicated by abnormal scPDSI (\(-\)0.72 compared to a mean 1.53) and reduced GPP (\(-\)16.02 \(\pm\) 6.15 gC/m\({}^{2}\)). The XCO\({}_{2}\) anomaly in Ex-10 could be explained by the increased temperature (2.55 \(\pm\) 1.07 K) and large GPP reduction (\(-\)26.91 \(\pm\) 20.88 gC/m\({}^{2}\)). The XCO\({}_{2}\) anomaly in Ex-9 could be explained by increased fire (with increased BA of 15.35 \(\pm\) 21.58 km\({}^{2}\)/grid), which is consistent with the wild fire that occurred in eastern Canada during that period discussed in [PERSON] et al. [71]. Detected abnormal XCO\({}_{2}\) over Ex-7 could be influenced by reduced local carbon uptake (with GPP of \(-\)4.99 \(\pm\) 9.74 gC/m\({}^{2}\)) and nearby high XCO\({}_{2}\) diffusion, transported from Eurasia as discussed in [PERSON] et al. [26]. However, no significant surface change is found over Ex-5, although the GPP is slightly reduced (\(-\)0.37 \(\pm\) 0.72 gC/m\({}^{2}\)). Some changes in the bare land or CO\({}_{2}\) transported in from nearby are discussed in Section 5.1.