Modern Warm Period Not Unprecedented, Chinese Academy Of Sciences Study Finds

  • Date: 23/08/17
  • Chinese Academy Of Sciences

 

2,000-year temperature reconstruction in China. Credit: Yang Liu & Jingyun Zheng

Advances in Atmospheric Sciences.

More information: Quansheng Ge et al, Characteristics of temperature change in China over the last 2000 years and spatial patterns of dryness/wetness during cold and warm periods, Advances in Atmospheric Sciences (2017). DOI: 10.1007/s00376-017-6238-8

Chinese Academy of Sciences, 8 August 2017

 

Characteristics of temperature change in China over the last 2000 years and spatial patterns of dryness/wetness during cold and warm period

Advances in Atmospheric SciencesVolume 34, Issue 8pp 941–951

Quansheng Ge et al., Chinese Academy of Sciences

Abstract

This paper presents new high-resolution proxies and paleoclimatic reconstructions for studying climate changes in China for the past 2000 years. Multi-proxy synthesized reconstructions show that temperature variation in China has exhibited significant 50–70-yr, 100–120-yr, and 200–250-yr cycles. Results also show that the amplitudes of decadal and centennial temperature variation were 1.3°C and 0.7°C, respectively, with the latter significantly correlated with long-term changes in solar radiation, especially cold periods, which correspond approximately to sunspot minima. The most rapid warming in China occurred over AD 1870–2000, at a rate of 0.56° ± 0.42°C (100 yr)−1; however, temperatures recorded in the 20th century may not be unprecedented for the last 2000 years, as data show records for the periods AD 981–1100 and AD 1201–70 are comparable to the present. The ensemble means of dryness/wetness spatial patterns in eastern China across all centennial warm periods illustrate a tripole pattern: dry south of 25°N, wet from 25°–30°N, and dry to the north of 30°N. However, for all centennial cold periods, this spatial pattern also exhibits a meridional distribution. The increase in precipitation over the monsoonal regions of China associated with the 20th century warming can primarily be attributed to a mega El Ni˜no–Southern Oscillation and the Atlantic Multidecadal Oscillation. In addition, a significant association between increasing numbers of locusts and dry/cold conditions is found in eastern China. Plague intensity also generally increases in concert with wetness in northern China, while more precipitation is likely to have a negative effect in southern China.

4. Conclusion

In this paper we report on a number of high-resolution proxies, paleoclimatic reconstructions, and new results through CCCP2k studies attained over the last five years. The following points can be concluded from this work:

(1) Multi-proxy synthesized reconstructions for China show significant cycles in temperature variation over the last 2000 years, including 50–70-yr, 100–120-yr, and 200–250-yr cycles. At the same time, the amplitudes for decadal and centennial variation in temperature are 1.3◦C and 0.7◦C, respectively, and centennial variation is significantly correlated with long-term changes in solar radiation—especially cold periods, which correspond approximately to sunspot minima, as well as the frequency of large volcanic eruptions. Results further show that the linear warming trend across the whole of China was 0.56◦ ±0.42◦C (100 yr)−1 for the period between AD 1870 and AD 2000. This was very likely the most rapid in the last 2000 years, although a similar warming rate also occurred in intervals between cold and warm periods before the 20th century. The warmth of the 20th century may not be unprecedented over the last 2000 years; the temperature of two peaks at AD 1080 and AD 1250 during the MCA are comparable.

(2) Spatial patterns in the dry–wet index ensemble mean for eastern China (i.e., the mainland region approximately east of 105◦E and south of 40◦N) across all centennial warm periods correspond to a tripole pattern of dry conditions south of 25◦N, wet conditions between 25◦N and 30◦N, and dry conditions north of 30◦N. In contrast, ensemble mean spatial patterns exhibit an east-to-west distribution for centennial cold periods, with wet conditions dominant east of 115◦E and dry conditions prevalent west of 115◦E, albeit with a wetness exception around 110◦E. An increase in precipitation in the monsoonal regions of China corresponding with 20th century warming can primarily be attributed to a mega-ENSO (one significant cause of interannual-to-interdecadal variations in global SST), as well as the AMO.

(3) Results show a significant association between the occurrences of locusts, human plagues, and long-term climate variation in eastern China, with more locusts recorded in dry and cold conditions. However, plague intensity responses to changes in wet and dry conditions are different in northern and southern China; plague intensity has generally increased with wetness in northern China, while high precipitation has historically had a negative effect in the south. These findings reported in this paper may improve our understanding of whether or not the warming observed in the 20th century can be considered exceptional within the past regional context. We have also explored changes in spatial patterns of dryness and wetness, as well as the temporal and spatial occurrences of locusts and plagues in China in response to climate warming, and our results provide insights for successful adaptation in the future. The results presented here will also be useful for further studies regarding the sensitivity of regional climate warming to CO2 concentrations, as well as climate dynamics, at decadal to centennial scales.

Full paper

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