GEOPHYSICAL RESEARCH LETTERS, VOL.26, NO. X, PAGES XXXX-XXXX, XXX, 1999
in press
Enhancement of the warming trend in China
Shaowu Wang and Daoyi Gong
Department of Geophysics, Peking University, 100871, Beijing, China
Abstract. The 1998 temperature averaged for the globe is
the highest on record. Annual mean temperature of China in
1998 is +1.38C above the normal, which also labels 1998
the warmest year since 1880 for China. Additional ice core
18O and tree ring evidence shows stronger upward trend (of
0.50C/100 years) than ever estimated based on temperature
observations in eastern coast region only during the last
hundred years. Enhanced warming trend has occurred in
most eastern Asia, the remarkable trend is making the middle-high continent of eastern Asia one of the rapidest warming regions in world during the last 2 decades. And the
warming time series in China indicates a sinusoidal variation
over the past hundred years and is different than for the
global average.
Introduction
Global averaged temperature has risen over the past hundred years by about 0.5C, and over half of the increase has
taken place during the past three decades. All ten top warmest years since the mid-19th century have occurred since
1980 [Jones et al.,1984; Jones,1994]. 1998 significantly
exceeded the previous average worldwide temperature record, which was established in 1997, and marks the fourth
time the record has been broken during the 1990s.
The warming is not uniform. Some cooling has taken
place in the North Atlantic, northeastern Canada and central
North Pacific. The regional temperature variation is important for us to understand the characteristics of global
warming in detail, and also, the possible influence of global
warming on the worldwide climate anomaly [Nicholls et
al.,1996].
The possible association of temperature over China with
global warming has also attracted close attention recently
[Wang, 1990, 1994; Wang and Ye, 1995]. A lot of evidence
showed the warmest period in China occurred during the
1940s, although global warming is prominent since 1980s.
Also, some earlier studies showed the warming trend in
China during the last hundred years is much weaker than
global mean temperature [Wang, 1990; Wang et al., 1998].
Here we will display the substantial evidence show there
is stronger upward trend than ever estimated for the annual
temperature of China over the past hundred years. Also we
will display that the stronger warming trend than global
mean has occurred in most eastern Asia during the last 2
decades, and demonstrate the temperature observed in 1998
was the warmest since 1880 in China.
Annual temperature series of China since 1880
Copyright 1999 by the American Geophysical Union
Paper number 99GLxxxxx.
xxxx
To estimate the warming trend in China, the reliable and
long temperature series are essentially important. Although
climate research relies greatly on the records from instruments at near surface weather stations, the modern large
networks of weather observing stations are operated beginning just in 1951 in China. During the past decades some
attempts have been made to estimate the annual mean temperature of China back to the late nineteenth century [Wang,
1990; Wang et al., 1998].
The earliest climate station is Beijing that began in 1841.
Although several other long-term stations, which located
almost in the east China near the coast, were established
during the late nineteenth and early twentieth century, there
are large gaps in the observed temperature coverage. Especially, the data availability over the western continent of
China is very poor. Historical documentary data, together
with other proxy data provide important supplement for increasing the coverage and extending back the data.
Chinese territory can be divided into ten regions according to inter-correlation among the 11 latitudelongitude
mean temperature records, which was provided by Chinese
Meteorological Institute and began in 1951. A large number
of correlation coefficients among annual temperature records
at all 966 grids show that there are ten regions, in each region the temperature change in an accordant way at the 95%
confidence level. The ten regions and their area weights are
listed in Table 1 (Also see Figure 2). Annual temperature
should be calculated for each region separately.
Table 1. Original Data Sources.
Area
Name
Period
Area
1880 To 1911 To 1951 To Weight
1910
1950
1998
1.North East Ob
Ob
Ob
0.131
2.North
Ob
Ob
Ob
0.084
3.East
Ob
Ob
Ob
0.043
4.South
Ob
Ob
Ob
0.059
5.Southeast Ob,HD Ob
Ob
0.011
6.Mid.South HD
Ob
Ob
0.072
7.Southwest HD
Ob
Ob
0.071
8.Northwest Ic
Ob
Ob
0.198
9.Xinjiang
Ic
Ic
Ob
0.149
10.Tibet
Tr
Ob,Tr
Ob
0.182
Ob-Observations, Tr-Tree ring data, Ic-Ice core
18O, HD-Historical Document.
Temperature data from 1911 to 1950 are digitized from
the Temperature Category Maps of China:1911-1980, [Center Meteorological Bureau, 1984], which contoured according to the early observations and covered the most east continent of China for the whole period of 1911-1950 and Tibet
in some years. During the period of 1880 to 1910, there are
only 4 regions have observations, for example, Harbin in
Region 1, Beijing in Region 2, Shanghai in Region 3,
Guangzhou and Hongkong in Region 4, Taibei in Region 5.
The early missed data of Harbin are corrected using the
temperature records of the near Russian and Japanese stations. The early temperature in Region 8 (i.e. the Northwest)
XXXX
WANG AND GONG: ENHANCEMENT OF THE WARMING TREND IN CHINA
1.0
XXXX
a
0.5
Temperature ( C )
0.0
-0.5
o
-1.0
1.0
b
0.5
0.0
-0.5
error bar
-1.0
1880
1890
1900
1910
1920
1930
1940
Year
1950
1960
1970
1980
1990
2000
Figure 1. Annual mean temperature anomalies of China. Curve a is calculated using four stations located in east China for
the period of 1880-1996 [Wang,1990], b is the series with complete coverage of all 10 regions of China and updated to 1998.
For series a, the linear trend is only 0.09C/100yr, but for b the trend increases to 0.50C/100yr, which is comparable to the
global warming trend of 0.5-0.6C/100yr. It shows the importance of data coverage when the mean temperature was calculated. Reference period is 1961-1990. Both smoothed with a 9-point Gaussian filter and shown in solid lines.
and 9 (i.e. Xinjiang) is reconstructed by using the 18O data
of Dende and Guliya ice cores respectively [Yao et al.,1990;
Yao et al.,1996], and in Region 10 (i.e. Tibet) calculated by
the tree ring data[Lin and Wu, 1977].
There are some causes maybe make temperature series ofthe
ten regions inhomogeneous, including the change of station
numbers for calculating the regional average [Jones et
al.,1997], the change of data source(especially the usage of
proxies).The regional mean temperature is measured by the
average of five stations during the past several decades, but
in the late nineteenth century there is only one station's records are available for most regions. The change of station
numbers maybe significantly change the variance of the regional temperature series. In most of the ten regions, the
variance of single station data is roughly close to that of average regional data. However, the standard deviation of Region 5 is 0.26, but that of Taipei (which locates in the north
of Taiwan) is 0.39. For the Region 4 and 8, the standard deviation ratio of regional data to the single center station data
is 0.76 and 0.77 respectively (Referenced to the period
1961-1990). We convert the temperature anomaly of single
station to the average regional anomaly by multiplying the
standard deviation ratio between them when there is only
single station data available in the early time. Regard of the
accordance of method, this multiplication is applied in all
regions. Proxies also are converted to the temperature series
with the same variance of observation temperature.
Finally, the annual mean temperature for the whole territory of China was established for the period of 1880 to 1998.
It's the first time to set up the series with consideration of the
complete coverage of all ten regions and their area size. And
the possible error in the early time of the temperature series
of China is also estimated. The error is measured as the variance of regional mean temperature unexplained by single
station's temperature or proxy series. For example, in Region
2 (i.e. North), there is 30.8% variance of regional temperature can not be explained by Beijing's temperature during the
past 4 decades. Because the standard deviation of the regional mean temperature is 0.44 in the same period, so there may
be 0.28C error if only use single station records of Beijing
to represent the regional mean. Possible errors of all 10 regions are estimated for the different periods. The error is
0.27C and 0.16C for 1880-1910 and 1911-1950 in average. The range of uncertainty in annual mean temperature
should to plus or minus 0.27C and 0.16C for 1880 to 1910
and 1911 to 1950 respectively, shown as the error bar in Figure 1.
Results and discussion
This annual mean temperature series can give us the best
possible estimate of temperature changes in China over the
last century. The trends appraised by some other authors
using less temperature data with incomplete coverage change
from 0.09 to 0.43C/100yr [Wang, 1990; Wang et al., 1998].
But as shown in Figure 1, one of the most apparent features
is the strong warming trend. The linear trend of the annual
temperature of China is 0.50C/100yr. This remarkable
warming trend is much higher than ever estimated before,
and comparable to the global mean trend of 0.5 to 0.6C per
100 years. Correlation of temperature between global mean
and China is 0.60 for the last 119 years. This infers good
parallelism of the warming in China with that on the globe.
Much surprisingly, there is a broad maximum from the 1920s
through 1940s, a dip between 1950s and early 1980s, and
another rise between the middle 1980s and the present. The
warming time series in China indicates a sinusoidal variation
over the past hundred years and is different than for the
WANG AND GONG: ENHANCEMENT OF THE WARMING TREND IN CHINA
50N
0.0
0.5
1.0
1.5
XXXX
o
2.5 C 3.0
2.0
1
9
40N
2
8
10
3
6
30N
7
4
5
20N
70E
80E
90E
100E
110E
120E
130E
Figure 2. Anomalies of annual surface air temperature of 1998 over the mainland of China. Reference period is 1961-1990.
Numbers indicate the ten regions, the names and area weights see Table 1.
90
60
30
0
-30
-60
-90
<-0.3
-0.3~0
0~0.3
-160
0.3~0.6
>0.6
-120
-80
-40
0
40
80
120
160
Figure 3. Annual surface temperature trends during the last two decades (1979-1998) at individual region [Jones et al., 1997,
updated], in degrees Celsius per 10 years. Area no data blanked.
global average.
It's of interest to notice that the 1998 also ranks as the
warmest year since 1880 in China[Gong and Wang, 1999a].
Temperature anomaly in 1998 is +1.38C (referenced to the
1961-1990 mean). The second warmest year occurred in1946,
temperature anomaly is +0.92, even considering the uncertainty of 0.16C, the possible rang is 0.76~1.08C, also
lower than +1.38C. It's manifest the annual temperature of
1998 set the highest record for the past century in China. As
shown in Figure 2, higher temperature anomalies take place
in the north, northern east, and Tibet in 1998 where temperature is 1.5~2.5C above the normal. In 1998, the highest
records of five months (February, April, September, October
and December) are broken according to the observations of
about recent five decades.
It is not by chance that 1998 saw the record for the highest annual temperature of China since 1880. It is reasonable
to be related with the rapid warming occurred in the last two
decades over the most eastern Asia. Figure 3 shows the
annual surface temperature trends during the period
1979-1998 at individual regions, in degrees Celsius per 10
years. Obviously, the middle and high latitude continental
Asia is the strongest warming region in world since the late
1970s. The linear trends in the central Siberia are above
WANG AND GONG: ENHANCEMENT OF THE WARMING TREND IN CHINA
0.6C/10yr. Most other regions over the eastern Asia also
have the warming rate between 0.3~0.6C/10yr. Warming
trend in annual temperature of China is 0.52C/10yr during
the last two decades, which is much higher than the global
mean trend of 0.19C/10yr.
Some studies have indicated that there are biases in the
surface temperature time series induced by the urban heat
island. Portman [1993] showed that the station temperatures
in or near the most highly and densely populated urban centers also exhibited this kind of biases over the northern plains
of China. And if the stations were undergoing changes of
rapid urbanizing, the temperature trend in the grid cell analysis such as shown in Figure 3 would be enhanced too. The
Most of China's big cities locate in the east, but as shown in
Table 1, these areas just account for little part of territory.
Over the middle and western China the urbanization is very
slow and the influence of urban on the temperature series is
generally believed inappreciable. Although it's difficult to
remove the urban bias entirely, the changes in the environment around the stations should be paid more caution and
need further studies.
However, these results showed that the recent upward
trends of temperature were not limited in China, but also
consistent to the warming token place over most of eastern
Asia. A key question regarding the genesis of recent climate
changes is how stronger warming trend have been maintained over much of the east Asia since late 1970s. The global warming may be one of the factors. Superimposed on the
longer-term trend, the interdecadal variability may be another factor in pushing the annual temperature upward [Schlesinger and Ramankutty, 1994],. But the trend of global mean
temperature is only 0.19C/10yr during the last two decades,
much weaker than that of China and most part of eastern
Asia, where the trends is above 0.3C/10yr over most regions. The influence of atmospheric circulation on the regional to large-scale temperature anomalies is emphasized
recently [Hurrell, 1995,1996;]. The Siberian High, which
measure the intensity of winter monsoon over eastern Asia
accounts for more than 40.0％ variance of the winter temperature over most part of China [Gong and Wang, 1999b].
But the warming in eastern Asia took place not only in winter, but also in other seasons, such as summer and fall. The
role that eastern Asia monsoon, including the summer monsoon, playing in the warming even remains to be unraveled.
XXXX
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______________
Acknowledgments. Special thinks to Dr. P.D. Jones, Climatic
S.W. Wang and D.Y. Gong, Department of Geophysics, Peking UniResearch Unit, University of East Anglia, UK, for making the glob- versity, Beijing 100871, P R. China. (e-mail: swwang@pku.edu.cn;
al temperature data available conveniently. This work was supported gdy@pku.edu.cn)
by National Natural Science Foundation of China under the grant
49635190, and by National Key Project of Studies on Short-term (Received
1999; revised
1999; accepted .)
Climate Prediction System in China under the grant 96-908-01. The
authors express their appreciation to two referees for useful comments on this paper.