A New 1787-2005 Temperature Reconstruction Determines The Coldest 50-Year Period Was 1940-1993

The warmest 50-year period in northeastern China occurred from 1844-1893.

Li et al., 2024

“Compared with single years, in general, high or low temperatures that persist for many years will more significantly affect the growth of trees [30]. When we defined years with T12-1 ≥ −10.73 °C (Mean + 1σ) and T12-1 ≤ −12.61 °C (Mean − 1σ) as extreme warm years and cold years, respectively, the reconstruction for the period of 1787–2005 contained 31 cold years and 36 warm years (Table 4). The extreme cold/warm events lasting for three or more consecutive years were discovered in 1965–1967 and 1976–1978/1791–1798, 1844–1849 and 1889–1891. An 11-year smoothing average of the reconstructed T12-1 series was performed to reveal multi-year and interdecadal variations and to detect the several prolonged cold and warm periods (Figure 5d). After smoothing with an 11-yr moving average, cold periods occurred in 1822–1830 (mean T12-1 = −12.7 °C) and 1957–1970 (mean T12-1 = −12.7 °C), while a warm period occurred in 1787–1793 (mean T12-1 = −10.4 °C) (Figure 5d). Rapid and sustained cooling was observed in the reconstructed series in the years 1790–1826 (T12-1 range −10.3 °C to −12.8 °C, mean = −12.0 °C) and 1939–1969 (T12-1 range −11.6 °C to −12.7 °C, mean = −12.1 °C), where the rates of cooling were about 0.067 °C/year and 0.035 °C/year, respectively (Figure 5d). The two cooling events may be due to the decrease in solar activity [48,49,50]. Using a 50-year time scale, the highest temperature occurring during 1787–2005 was from 1844 to 1893 (T12-1 range −12.79 °C to −9.41 °C, mean = −11.15 °C), similar results were also obtained by Zhu et al. and Jiang et al., while the lowest temperature was from 1940–1993 (T12-1 range −13.57 °C to −10.26 °C, mean = −12.13 °C) (Figure 5d) [33].”

“Recent studies have underscored the strong correlation between changes in Earth’s climate and solar activity. The prevailing belief is that during periods of lower solar activity, such as the Dalton Minimum (c. AD 1790–1830) [51,52,53], Earth’s temperature is expected to decrease. Our reconstruction reflects these expectations, displaying low values from AD 1790 to 1830 that coincide with the Dalton Minimum of diminished solar activity (Figure 7a). Conversely, during periods of heightened solar activity, the climate tends to warm, as observed during the Roman warm period (400–10 BC) and the medieval warm period (900–1200 AD) [53]. It was found that the upper temperature of the troposphere and stratosphere was synchronous with the 10–12 years cycle of solar activity [54]. The 12.9 years cycle correspond with the sun spot cycle [55,56,57,58]. Correlation analyses revealed a significant positive correlation between the annual reconstructed T12-1 and the number of sunspots from the previous December to the current January, with r = 0.22 (N = 188 years, 1818–2005, p = 0.011). The 73-year cycle may be linked to the 50–80 years Lower Gleissberg cycle [31], reflecting changes in solar radiation intensity [57]. A noteworthy relationship between the reconstructed series and sunspot numbers was identified during specific periods, including the 1790s–1840s, 1850s–1870s, 1920s–1930s, and 1950s–2000s (Figure 8B). Additionally, other studies in northern China have also detected cycles of approximately 10 years [25,58,59] and approximately 70 years [45], suggesting potential effects of solar activity in the region.”

Image Source: Li et al., 2024