Modern Warm Period Not Unprecedented, Chinese Academy Of Sciences Study Finds
“We found four warm epochs,” says Prof. Quansheng Ge. Data show records for the periods AD 981–1100 and AD 1201–70 are comparable to the present warm period.
2,000-year temperature reconstruction in China. Credit: Yang Liu & Jingyun Zheng
A great deal of evidence relating to ancient climate variation is preserved in proxy data such as tree rings, lake sediments, ice cores, stalagmites, corals and historical documents, and these sources carry great significance in evaluating the 20th century warming in the context of the last two millennia.
Prof. GE Quansheng and his group from the Institute of Geographic Sciences and Natural Resources Research of the Chinese Academy of Sciences, collected a large number of proxies and reconstructed a 2000-year temperature series in China with a 10-year resolution, enabling them to quantitatively reveal the characteristics of temperature change in China over a common era.
“We found four warm epochs, which were AD 1 to AD 200, AD 550 to AD 760, AD 950 to AD 1300, and the 20th century. Cold periods occurred between AD 210 and AD 350, AD 420 and AD 530, AD 780 and AD 940, and AD 1320 and AD 1900. The temperature amplitude between the warmest and coldest decades was 1.3°C,” said Prof. GE.
The team found that 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 in the last 2000 years, as reconstruction showed records for the period from 981 to 1100, and again from 1201 to 1270, were comparable to those of the present warm period, but with an uncertainty of ±0.28°C to ±0.42°C at the 95% confidence interval. Since 1000 CE—the period covering the Medieval Climate Anomaly, Little Ice Age, and the present warm period—temperature variations over China have typically been in phase with those of the Northern Hemisphere as a whole.
They also detected some interactions between temperature variation and precipitation change. 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. For all cold periods, the ensemble mean drought/flood spatial patterns showed an east to west distribution, with flooding east of 115°E and drought dominant west of 115°E, with the exception of flooding between approximately110°E and 105°E.
The general characteristics of the impacts of climatic change historically were negative in the cold periods and positive in the warm periods. For example, 25 of the 31 most prosperous periods in imperial China during the past 2000 years occurred during periods of warmth or warming. A cooling trend at the centennial scale and social economic decline run hand-in-hand. The rapid development supported by better resources and a better environment in warm periods could lead to an increase in social vulnerability when the climate turns once more to being relatively colder.
“Throughout China’s history,” Prof. GE added, “both rulers and the ruled have adopted strategies and policies to cope with climate change, as permitted by the prevailing geography and circumstances of the time.”
The study is published in 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
Characteristics of temperature change in China over the last 2000 years and spatial patterns of dryness/wetness during cold and warm period
Quansheng Ge et al., Chinese Academy of Sciences
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.
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.