Paleoclimate Study From China Suggests Warmer Temperatures in the Past

By Anthony Watts – Re-Blogged From http://www.WattsUpWithThat.com

People send me stuff. Today in my inbox, WUWT regular Michael Palmer sends this note:

My wife Shenhui Lang found and translated an interesting article from 1973 that attempts the reconstruction of a climate record for China through several millennia (see attached).  The author is long dead (he died in 1974), and “China Daily” is now the name of an English language newspaper established only in 1981. I think it would be very difficult to even locate anyone holding the rights to the original, and very unlikely for anyone to take [copyright] issue with the publication of the English translation.

The paper is interesting in that it shows a correlation between height of the Norwegian snow line and temperature in China for the last 5000 years.


 

A Preliminary Study on the Climatic Fluctuation during the last 5000 years in China

Zhu Kezhen

Published in China Daily, June 19th, 1973 / translated by Shenhui Lang, PhD

Chairman Mao taught us that “In the fields of the struggle for production and scientific experiment, mankind makes constant progress and nature undergoes constant change, they never remain at the same level. Therefore, man has constantly to sum up experience and go on discovering, inventing, creating and advancing. Ideas of stagnation, pessimism, inertia and complacency are all wrong. They are wrong because they agree neither with the historical facts of social development over the past million years, nor with the historical facts of nature so far known to us (i.e., nature as revealed in the history of celestial bodies, the earth, life, and other natural phenomena).” Some believe that there was no climate change in the human history. This idealistic type of argument has been proven wrong based on the Chinese historical records.

There are abundant records of meteorology and phenology in the Chinese historical documents, which unfortunately are scattered. This article is a preliminary analysis of the climate change based on the available historical records, hoping to draw an outline of the major trend of climate change in the past 5000 years in china.

In the monsoon area of East Asia, the annual rainfall often varies greatly. However, the temperature during winter and spring can have a direct effect on the growth of the crops. The winter temperature in China is mainly controlled by the Siberia cold front, therefore, the rise and fall in winter temperature are usually consistent across China. In this article, the winter temperature is used as an indicator to analyze the climatic change. The 5000-year span has been divided into four periods according to the nature of the available sources.

1. Archaeological Period (3000 to 1100 B.C) without written records except scripts on oracle bones.

The remains of subtropical and tropical animals such as Asian water buffalo (Bubalus bubalis) and Chinese bamboo rats (Rhizomys sinensis) were found at Banpo Village of Yangshao Culture (carbon-14 dating 6080 to 5600 BC) near Xi’an, Shaanxi and Yinxu (Ruins of Yin, 1400 to 1100 BC), Anyang, Henan. There are no such animals living in these areas anymore now. According to the oracle bone records from the Yin Dynasty (1600 to 1046 BC), the sowing time of rice was about one month earlier than the current sowing time. A piece of charred bamboo stem was found at an archaeological site of the late Neolithic Longshan Culture (3000 to 1900 BC), Licheng, Shandong. The outer appearances of some pieces of pottery seem to have a pattern of bamboo stem. These two findings indicate that bamboo was distributed from the Yellow River valley area to the east coast of China in the late Neolithic Age. Based on this evidence, we can speculate that the northern limit of bamboo distribution has moved by 1° to 3° latitude towards the south during the last 5000 years. By comparing the temperatures of the lower reaches of Yellow River and Yangtze River, it is safe to believe that the period from the Yangshao Culture to the Yin Dynasty (3000 to 1100 BC) was a warm period. The annual average temperature was about 2°C above the current temperature. The average temperature in January was about 3 – 5°C higher than now.

2. Phenological Period (1100 BC -1400 AD) without detailed regional records

As summer goes and winter comes, people can study the seasonal and inter-annual variations of the climate by observing the timing of appearance of frost and snow, freezing and thawing of rivers, and emergence of leaves, flowers and fruits, and the dates of migratory birds’ first and last appearance. This is phenology. Phenology can also be called climatology and meteorology without instrumental records. Chinese people have started observing phenological events since 11th century BC, accumulating a wealth of data spanning 3000 years.

Pictograms and simple ideograms are the basic components of Chinese characters. Characters in pictograms directly evolve from the pictures of objects they represent. Characters in ideograms have direct iconic illustrations. By combining two or more pictographic or ideographic characters, a new character with a third meaning can be created. Chinese characters in the documents from early Zhou Dynasty (1066 BC, with its capital Haojing near Modern Xi’an) that depict clothing, household utensils, books, furniture, and musical instruments all contained the character of bamboo (竹), suggesting that they were originally made of or from bamboo. These characters in the documents from early the Zhou Dynasty indicate that bamboo was grown extensively in the Yellow River Valley.

It is impossible to grow bamboo in these areas now. During the Shang and Zhou dynasties (1766-256 BC), most people worked in agriculture and animal husbandry. Seasonality was very important to them. Various methods were used to determine the spring equinox, which was usually the start of spring plowing. At that time, farmers in the Tan kingdom (today’s Tancheng Shandong) observed that barn swallows (Hirundo rustica gutturalis) in spring would first show up around the Spring Equinox time. At present barn swallows return to Shanghai, the lower reaches of Yangtze River around March 22nd, approximately the Spring Equinox time. The barn swallows will reach Tancheng a few days later. The annual average temperature difference between Tancheng and Shanghai during the 5-year period between 1932-1937 was 1.5 °C (see Table 1), while the temperature difference in January was 4.6°C. This result is consistent with the conclusion based on bamboo distribution during the archaeological period.

The warm climate in the early Zhou dynasty deteriorated very soon. The Han river became frozen in 903 BC and 897 BC. However, the weather got warmer during the Spring and Autumn Period (770-481 BC). It was mentioned in the book “Zuo Zhuan” (Commentary of Zuo) that ice could not be produced and stored in the cold sheds in winter in the Lu kingdom, Shandong. In the middle of the Zhou dynasty, plum trees were grown extensively in the lower reaches of the Yellow river. Plums were mentioned five times in “Shi Jing” (The Book of Songs). There are such verses as “What grows on Zhongnan mountain? White firs and plum trees” in the poem “Zhongnan”, “Qin Feng”, “Shi Jing”(Ballads of Qin, The Book of Songs). Zhongnan mountain is located to the south of Xi’an, where no plum tree grows at present, whether wild or cultivated. Plum was also a popuplar seasoning in cooking during the Shang and Zhou dynasties (1766-256 BC), since vinegar was not known yet, indicating the wide distribution of plum trees.

During the Warring States period (475-221 BC) and the Qin (221-207 BC) and Han (207 BC-AD 220) dynasties, the climate remained warm. Zhang Biao in the early Qing dynasty (AD 1644-1912) studied the phenological events recorded in “Lu Shi Chun Qiu” (The Annals of Lu Buwei), which was completed in 241 BC. He concluded that the phenological events in the early spring during the Warring States period was three weeks earlier than the early Qing dynasty. Sima Qian (135 or 145 -86 BC) during the Han dynasty described the distribution of subtropical crops in “Shi Ji” (Records of the Grand Historian). Examples were orange trees grown in Jiangling, Sichuan, mulberry in Qilu, Shandong, bamboo in Weichuan, Shaanxi, and laquer tree in Chenxia in the south of Henan. The northern limits of these subtropical plants have moved towards the south since then. The Yellow River breached at Huzi in 110 BC. Baskets carrying stones made of bamboos grown in Qi Garden of Henan were used to stop the flood, suggesting the abundance of bamboo then in Henan.

During the East Han dynasty (AD 5-220), there was a distinct trend of climate cooling. There were several severe winters. Frost and snow were recorded in the late spring. But this cooling period didn’t last long. At that time, oranges and mandarins were still common in the south of Henan. During Three Kingdoms period (AD 220-280), Cao Cao (AD 155-220) managed to grow orange trees in the garden of his Bronze Bird Palace (today’s Southwest Linzhang, Henan). However, these orange trees were unable to bear fruit. The weather was much colder than the period in which Sima Qian (135 or 145-86 BC) had lived.

Cao Pi, son of Cao Cao, inspected a military exercise of 100,000 soldiers at Guangling, Huai’an (today’s Huaiyin) in AD 225. Because of the sudden severe cold, the Huai river became frozen and the drill had to be aborted. This is the first written record of Huai river freezing over. At that time, the weather was much colder than now. The cold period went on until the second half of the 3rd century, reaching the peak between AD 280 and 289. At that time, frost would still appear in the 4th month of Chinese lunar calendar (approximately May in the western calendar). One can estimate that the annual average temperature in the 3rd century was 1-2 °C lower than today.

During Southern and Northern Dynasties (AD 420-579), cold sheds were built to preserve food on the hill of Fuzhou, Nanjing. The winter temperature in Nanjing in those days must have been 2°C lower than now to provide the ice for food preservation. The book “Qi Min Yao Shu” (Essential Techniques for the Welfare of Common People) published in AD 533-544 was a comprehensive agricultural manual, summarizing the Chinese agricultural techniques used in this period. In the areas to the north of Yellow River, apricot trees blossomed in April, and leaves of mulberry trees emerged in early May according to this book, which is about 2 to 4 weeks later compared to today. In addition, it was also mentioned in this book that people in the Yellow River walley winterized pomegranate trees by covering and wrapping the trees with cattails, indicating that the weather in the first half of the 6th century was colder than now.

China became a united country during the Sui and Tang dynasties (AD 581-907). The climate had become warmer starting from the middle of the 7th century. There was no ice forming and snow falling in capital of the Tang dynasty, Xi’an in AD 650, 669, and 678. From the early 8th century to the middle 9th century, plum and orange trees were grown in the garden of the Royal Palace in Xi’an and Lake Qu in its southern suburb. The orange trees in the Royal Palace produced fruits in AD 751. There were also records of orange fruit harvesting between AD 841 and 847. The orange tree can withstand a minimal temperature as low as -8 °C. Today, the lowest winter temperature in Xi’an every year is invariably below -8 °C.

In the early 11th century, there would have been no plum trees in northern China. The poem “Apricot” by Su Shi (AD 1036 – 1101), a famous poet in Song Dynasty, contains the following line: “Fortunately, there is no plum tree in the central Shaanxi plain”. Wang Anshi (AD 1021-1086) from the same period laughed at people from northern China for mistaking plum trees for apricot trees. There are such lines as “Northerners don’t know the plum trees, mistaking them for apricot trees” in his poem “Ode to the Red Plum Blossom”. From these general phenological events, we can tell the temperature difference between Tang and Song Dynasty.

At the beginning of the 12th century, climate cooling in China accelerated. The whole water body of Lake Tai was frozen in AD 1111. Vehicles could travel over the frozen Lake Tai. All orange trees in the areas of Lake Tai and Dongting Hill died of frost. Snow was very common in Hangzhou then, and the snowy season lasted till late Spring. According to the historical records of the southern Song dynasty, the average date of last snow fall during a 10-year period from AD 1131-1260 was April 9th, approximately one month later than the average date of last snow fall during a 10-year period before the 12th century. Southern Canal near Suzhou froze in winter from AD 1153-1155. In October of 1170, West Hill in Beijing was covered with snow, which is rare today.

Fuzhou on the east coast of China is the northern limit of lychee growing range. In the last 1000 years, incidents of all lychee trees perishing during winter in Fuzhou were reported twice. Both incidents occurred in the 12th century, once in AD 1110 and another time in AD 1178.

Japanese feudal lords held cherry (Prunus serrulata) blossom viewing parties in Kyoto every year from the 9th to 19th century. These parties were all recorded with exact dates, providing a complete phenological record of Japanese cherry blooming dates (see Table 2). The earliest date of full bloom of cherry was observed in the 9th century, while the latest occurred in the 12th century.

Right after the 12th century, the winter in Hangzhou started getting warmer. There was no record of ice and snow in AD 1200, 1213, 1216, 1220 in Hangzhou. During the same period, the apricot trees bloomed around the Festival of Qingming (the 5th solar term) in Beijing, similar to the blooming dates of apricot today. It seems that the warm weather lasted into the late 13th century, from the fact that the departments supervising and managing bamboo production in Henei (today’s Boai Henan), Xi’an, and Fengxiang (Shaanxi), which had been established since the Sui and Tang dynasties (AD 581-907), continued to run intermittently during the Song (AD 960-1279) and Yuan dynasties (AD 1271-1368) but had stopped functioning completely at the end of the Ming dynasty (Ad 1368-1644). Since then bamboo has not been grown as as a crop plant to the north of Yellow River.

The warm period during the early and middle 13th century was short. The winter became cold shortly after. According to the available records, the canal along Wuxi, Jiangshu, became frozen in AD 1309. The ice of Lake Tai was several feet thick. Orange trees again perished in the winter. Ice floes were observed floating in the Yellow River in Shandong in November 1351, whereas nowadays they only appear in December in Henan and Shandong. During that period, barn swallows appeared at the end of April in Beijing and left at the beginning of August. The date of barn swallow appearance was approximately one week later, while the date of barn swallow leaving was one week earlier compared to current observations. Therefore, it was colder in the 14th century than in the 13th century and today. The phenological records of Japanese cherry blooming also show a similar trend (see Table 2).

Qiu Chuji travelled from Beijing to West Asia to visit Genghis Khan in 1221, passing through Sayram Lake (Xinjiang) which he called “Lake of Heaven”. According to his travel notes, the lake was surrounded by snow-covered mountains (the Tianshan Mountains). However, there is no snow in these mountains today. The peaks that surround the lake are about 3500 meters high, indicating that the snow line was below 3500 meters at that time. Today the snow line in the Tianshan Mountains is about 3700 to 4000 meters high. Therefore the snow line of Tianshan Mountains in the 13th century was about 250 meters below the current level. The cold period started around 1350 in the European part of the Russian Plain. The period between 1429 and 1465 marked the beginning of climatic deterioration in German and Austrian areas. Bad harvests in England in 1430, 1550, and 1590 were also associated with the cold weather. Thus it is obvious that the climate cooling started from East Asia and gradually moved towards the West.

3. Period with Local Records

Based on 665 local records, years in Lake Tai, Lake Boyang, Lake Donting, Han River and and Huai River froze in the winter (13th to 20th century) and years with snow and frost in the tropical area near sea level were summarized (see Table 4). These records indicate that warm winters occurred during the periods of 1550-1600 and 1720-1830 and cold winters occurred during the periods of 1470-1520, 1620-1720 and 1840-1890. The coldest century is the 17th century, and the 19th century comes second. These results are consistent with the number of years of frozen Lake Suwa in Japan (latitude 36ºN, longitude 138ºE) and the number of days for which Lake Suwa remained frozen in the winter (see Table 5), except that the start and the end of severe winters in Japan are a quarter of century earlier than in China.

As mentioned above, the winters from the 15th century to the 19th century were relatively cold, the coldest winters occurred in the 17th century, especially during the period from 1650-1700. For example, the orange and tangerine orchards were completely destroyed in the winters of 1654 and 1676. During this 50-year period, Lake Tai, Han River and Hui River were frozen 4 times and Lake Dongting was frozen twice (see Table 3). In the tropical parts of China, the occurrence of snow and frost was also very frequent. There are records of blooming dates of peach, apricot, lilac and Chinese crabapple trees in the current area of Sha City of Hubei province from 1608 to 1617. Comparison of these data to the current data obtained from Wuchang of Hubei Province shows that the blooming dates were about 7 to 10 days later than now.

The phenological records from Beijing from 1653 to 1655 are also around 1 to 2 weeks later than now. According to the travel journal by Tan Qian, who traveled from Hangzhou to Beijing at that time, the canal in Tianjin was already frozen on 18th of November, 1653, making boat travel to Beijing impossible. Tan Qian thus had to go to Beijing by carriage. On his way back to Hangzhou in 1656, he noted that the canal in Beijing was thawed on the 5th of March. Therefore, the freezing period at that time lasted 107 days, whereas the current freezing period lasts only 56 days. Overall, based on the phenological records, one can estimate that the temperature in Beijing at that time was 2ºC below current temperatures.

4. Period of Instrumental Records

During the Qing Dynasty (1644 -1910), there were records of rainfall of Beijing, Nanjing, Hangzhou and Shuzhou. Based on the average dates of first snow in fall and last snow in spring, we can conclude that the weather from 1801-1850 was warmer than the previous period of 1751-1800 and the following period of 1851-1900. This conclusion is consistent with the local records cited in the previous section.

From the temperature records of Shanghai, the temperature in the last quarter of the 19th century was the coldest. The winter temperature moved up to the average around 1897. Afterwards the winter temperatures had remained above the average for 14 years. From 1910-1928, the winter temperatures dropped below the average. Then the temperature moved up and the winter temperatures from 1945-1950 were 0.6ºC higher than the average. Afterwards, the temperature gradually decreased. In 1960, the temperature dropped back to the average. During the same period, the winter temperatures in Tianjin also showed a trend similar trend to that of Shanghai; however, both the peak point and lowest point arrived a few years earlier than that of Shanghai. The range of temperature fluctuation of Tianjin is wider than that of Shanghai. The peak point and lowest point of temperature of Hongkong arrive later here than in Shanghai, and the range of temperature fluctuation is again narrower. In the last eighty years, the temperature in Shanghai fluctuated in a range of 0.5-1 ºC. This type of temperature fluctuation can have a direct effect on the growth of plants and animals, which in turn will affect the occurrence of plant diseases and pests, and therefore will also have an impact on agricultural operation and production.

The changes in temperature in the last 80 years have already made an impact on the snow line of the Tianshan Mountains and the retreat of glaciers. According to the studies done by the glacier research team of Chinese Academy of Sciences, the snow line of the Tianshan Mountains has gone up 40 to 50 meters and western glaciers have retreated 500 to 1000 meters during the 50-year period from 1910-1960. The glaciers east of the Tianshan Mountains have retreated 200 to 400 meters. The upper limit of tree line has also moved up a little. The current glacial cover of the Tianshan Mountains was formed during the cold period of 1100-1900; it does not consist of remnants from the 4th [intended meaning probably: the most recent] Glacial Period. Freshly formed glacial accumulations could easily be distinguished from the remnants from of the ancient glaciers based on the extent of weathering, the surrounding soil and vegetation.

Preliminary Conclusions:

1. During the first 2000 years of our 5000-year civilization, most of the time, the annual average temperature was 2ºC higher than now. The temperature in January was 3-5ºC higher than now.

2. From then on, there was a series of temperature fluctuations. The lowest temperatures occurred in AD 1000, 400, 1200, and 1700. The range of fluctuation was 1-2ºC.

3. In every 400-800 period, a smaller cycle lasting 50 to 100 years can be detected with a temperature range of 0.5 -1ºC.

4. During the above cycles, it seems that any coldest period started from the Pacific coast of East Asia. The cold waves then moved westward to Europe and the Atlantic coasts. And at the same time, there were also trends from the North to the South.

We compared the temperature changes in Europe with those in China since the 3rd century. We found that the temperature fluctuation curves of the two areas were related. In the same cycle, the wave motion of temperature change of Europe usually started later than that of China. Because the rise and fall of the snow line in the same area is closely related with the temperature change. We compared our results with the Norwegian snow line (see Figure 1). similar pattern is observed, with only a difference in timing. There was a cold period in Norway in 400 BC while no such cold period was observed in China at that time.

clip_image002

Figure 1: Height of the Norwegian snow line (solid line; left Y axis) for the last 10,000 years and temperature in China for the last 5000 years (dashed line; right Y axis).

Recently, scientists from the University of Copenhagen profiled the climate record of the Greenland ice sheet using the 18O/16O isotope method. The rise and fall of the temperature in Greenland in the last 1700 years showed similar profile to what we concluded in this article (see Figure 2). Besides, there was a cold period in China 3000 years ago. Similar climate record was also reflected in 18O/16O isotope data.

clip_image004
Figure 2: Comparison of temperature variation in China (A) and the Greenland ice sheet 18O/16O isotope ratio, since approximately 300 AD.

In this article, we profiled the ancient climate changes using the phenological method. Phenology is an ancient climatic indicator while using the ratio of 18O/16O isotope to determine the temperature of historical ice and water is a modern method. Similar conclusions could be reached using these two different methods. Finding out the pattern of climate change in the past could be beneficial to the long-term weather forecast. Under the guidance of Marxism-Leninism and Mao Zhedong’s Thought, it may be possible to predict the long-term climate cycle could be predicted by making full use of our abundant historical phenological and archaeological records.


About the author

Zhu Kezhen (1890-1974) was a Chinese meteorologist and geologist. He graduated from the School of Agriculture, University of Illinois, and obtained his PhD in Meteorology from Harvard University. From 1920, he had successively served as chair of Department of Meteorology, Nanjing University, director of Chinese Institute of Meteorology, Academia Sinica, president of National Chekiang University (now Zhejiang University), and vice president of the Chinese Academy of Sciences.

A PDF of this complete paper is available here: zhukezhen english3(PDF)

 

Tables

 

Table 1: The difference of average temperature between Tancheng and Shanghai during the period of 1932-1937.

City Latitude (N) Longitude (E) Altitude (m) January(°C) February(°C) March(°C) AnnualAverage
Tancheng 34°38′ 118°26′ 20.0 -1.4 1.0 6.6 14.1
Shanghai 31°32′ 121°26′ 7.0 3.2 4.2 8.1 15.6
Difference 3°6′ 4.6 3.2 1.5 1.5

 

Table 2: Frequency of recorded dates of Japanese cherry blossom and the average dates from the 9th -20th century

Century Frequency of Recorded Dates of Cherry Blossom (%) No. of Observations Average date
BeforeMarch 31st April1st – 10th April11th– 20th April21st – 30th AfterMay 1st
9th / 43 57 / / 7 April 11th
10th 7 36 50 7 / 14 April 12th
11th / 20 40 40 / 5 April 18th
12th / 25 25 25 25 4 April 24th -25th
13th 13 13 38 38 / 8 April 15th
14th / 8 58 25 8 12 April 18th
15th / 43 47 17 3 30 April 13th
16th / 3 77 13 6 31 April 18th
17th 10 20 70 / / 40 April 12th
18th / / / / / / /
19th / 20 89 / / 5 April 12th
20th blossom start 8 61 31 / / 36 April 7th
20thfull bloom / 31 61 9 / 36 April 14th

Table 3: Years of frozen lakes and rivers in the Yangtze River valley

Year Lake Tai Lake Boyang Lake Dongting Han River Hui River
1901-1970 1955 1955 1955
1900
4th quarter 1877, 1893 1877 1877, 1886, 1899
3rd quarter 1861 1861, 1865 1865, 1871
2nd quarter 1840 1830 1845
1st quarter
1800
4th quarter 1790
3rd quarter 1761
2nd quarter
1st quarter 1715, 1720
1700
4th quarter 1683, 1700 1690 1690, 1691 1690
3rd quarter 1654, 1665 1670 1653, 1660 1653, 1660, 1670 1653, 1670, 1671
2nd quarter 1640
1st quarter 1621 1620, 1621 1619
1600
4th quarter 1578
3rd quarter 1568 1570 1564
2nd quarter 1529 1550
1st quarter 1503, 1513 1513 1510, 1513 1519
1500
4th quarter 1476 1493
3rd quarter 1454 1454
2nd quarter 1449
1st quarter 1416
1400
4th quarter
3rd quarter 1353
2nd quarter 1329
1st quarter
1300 1219
Before 1200 1111 -879, -901 225, 515, 1186

Table 4 Years with snow and frost in the tropical area close to the sea level in China

A Quarter of a Century Year
1900
4th quarter 1878, 1882, 1893
3rd quarter 1854, 1856, 1862, 1871, 1872
2nd quarter 1831, 1832, 1835, 1840, 1846
1st quarter 1824
1800
4th quarter 1781
3rd quarter 1757, 1758, 1763, 1768
2nd quarter 1729, 1737, 1742
1st quarter 1711, 1713, 1721
1700
4th quarter 1681, 1682, 1683, 1684
3rd quarter 1654, 1655, 1656
2nd quarter 1635, 1636
1st quarter 1602, 1606, 1621
1600
4th quarter 1578
3rd quarter
2nd quarter 1532, 1536, 1537, 1547, 1549
1st quarter 1506, 1512, 1522
Before 1500 1245, 1415, 1449

Table 5 Number of Days during which Lake Suwa remained frozen

A quater of a century Number of non-frozen years Days later (+)/ or earlier (-) than the average first day of frozen lake
1900
4th quarter 2 -4.9
3rd quarter 5 +21.3
2nd quarter 2 +7
1st quarter 3 +1.4
1800
4th quarter 2 +3.5
3rd quarter 2 +2
2nd quarter 3 +8.2
1st quarter 3 +10.1
1700
4th quarter 0 -4.7
3rd quarter 1 -4.7
2nd quarter 0 -6.3
1st quarter 0 +10.2
1600
4th quarter 0 -4.9
3rd quarter 1 -3.2
2nd quarter 1 -3.3
1st quarter 9 +12
1500
4th quarter 0 -6.8
3rd quarter 1 -11.7

 

Table 6 Annual and monthly average temperatures in Beijing during the periods of 1757-1762, 1875-80 and 1954-64.

January February March April May June July August September October November December Annual
1757-62 -5.0 -4.1 3.5 13.0 20.4 25.6 26.0 25.6 19.6 12.2 3.0 -3.4 11.4
1875-80 -5.8 -1.9 5.5 14.2 20 25.6 26.9 25.5 19.5 12.0 3.2 -3.4 11.8
1954-64 -4.2 -1.8 4.6 13.9 20.1 24.1 26.0 24.7 19.6 12.1 4.3 -2.4 11.8
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