From the report.... not the dodgy contextomy opinions about the report.
ERA5 reveals a cooling trend in austral summer in the Antarctic Peninsula, and Turner et al. (2016) have pointed out that the most rapid cooling trend occurs in the austral summer, and this drop is related to more frequent cold, east-to-southeasterly winds. Sea ice plays an important role in the temperature over the Antarctic Peninsula, and the changes in sea ice extent and duration are mainly controlled by Southern Annular Mode (SAM) and El Niño-Southern Oscillation (ENSO) [13,48,49]. The decline in stratospheric ozone concentrations is a part reason for the increase in the circumpolar westerlies and may account for the warming trends in the peninsula region in austral summer and autumn [50]. West Antarctic continental temperature increases primarily in austral winter and spring, and research concluded that the increasing tropical sea surface temperature affects the high-latitude atmospheric circulation in the Southern Hemisphere, which may accounts for the West Antarctic warming [50]. In ERA5, East Antarctica displays warming trends in spring, and significant warming is concentrated in the region above 80°S latitude. A cooling trend occurs in MAM and DJF, and the regional cooling is likely related to tropospheric flow, which is promoted by atmospheric circulation changes [15,51,52]. The cooling trend of ERA5 in East Antarctica indicates that ERA5 can describe the ozone-forced cooling of the troposphere that has been observed in the region since the late 1970s [15].
There are several temperature reconstructions in Antarctica based on different methods [11,53,54]. Monthly near-surface temperature anomalies in Antarctica for the period 1958–2012, based on 15 monthly instrumental temperature observations in combination with spatiotemporal temperature covariances, from CFSR (RECONCFSR) show the best performance [15]. Figure 11 compares the annual temperature trends for the entire Antarctic continent from RECONCFSR and ERA5 during the period 1979–2012. The trends of ERA5 are highly different from those of RECONCFSR. Positive trends occur in almost all grids of RECONCFSR over the Antarctic Peninsula, while ERA5 shows a negative trend over the northern Antarctic Peninsula islands. The opposite trends are found over East Antarctica; in particular, a significant cooling trend in central Antarctica is shown in the ERA5 output. From 1979 to 2010, an extensive negative trend predominated East Antarctica in 20CR, a positive trend was dominant in Antarctica in ERA-20C [28], while a positive trend occurs in northern East Antarctica in ERA5 in comparison. Figure 11. Trends in annual mean temperature from RECONCFSR and ERA5 during the period 1979–2012. The gray shaded areas with trends significant at the 95% confidence level. 5. Conclusions
Based on the monthly near-surface air temperature from 41 weather stations in Antarctica, compared with that of ERA-Interim, the performance of ERA5 has been assessed in all of Antarctica and the three subregions namely East Antarctica, West Antarctica, and the Antarctic Peninsula. The variability in annual and seasonal mean temperature can be reproduced by ERA5, although bias occurs. Over the whole of Antarctica, ERA5 presents a cold bias with the exception of JJA, while ERA-Interim shows a cold bias in all annual and seasonal means. The two reanalyses exhibit lower bias at coastal stations in all cases, and the lowest correlation occurs in DJF. For all stations, the correlations between ERA5 and monthly observations are higher than 0.95, indicating a high linear relationship and good performance, and the difference between ERA5 and ERA-Interim is lower than 0.01. The significant correlations of ERA5 are higher than 0.80 at most stations in annual and seasonal mean temperatures. Generally, ERA5 has the highest linearity in SON, with significant correlation coefficients higher than 0.90, and the lowest linear relationship is shown in DJF. There are regional differences in ERA5 capacity, with high correlations in West Antarctica and the Antarctic Peninsula. Compared with ERA5, ERA-Interim has a slightly higher linear relationship with observations in the Antarctic Peninsula. Warm bias in ERA5 prevails for the stations located in the interior of the Antarctica, and the biases for coastal stations are irregular. ERA5 shows a warm bias in East Antarctica except in JJA, a cold bias in West Antarctica and a warm bias on the Antarctic Peninsula. ERA5 exhibits the opposite biases in comparison with ERA-Interim in the three subregions in JJA. A cooling trend occurs in ERA5 and ERA-Interim over East Antarctica, and a warming trend occurs over the Antarctic Peninsula with the exception of DJF. We conclude that ERA5 performs well in Antarctica, but it is necessary to correct the biases to improve the reanalysis. Despite the bias present in ERA5, in Antarctica, with sparse in situ observations, ERA5 is the most up-to-date reanalysis model and can play an important role as an effective tool to study climate change.
