Impacts of the Human Emisions on Climate Change in China
as Simulated by Multi-model Ensembles
Zong-Ci Zhao, Yong Luo, Xuejie Gao, Ying Xu, and Yihui Ding
Laboratory for Climate Research, Meteorological Administration,
corresponding e-mail: email@example.com
The impacts of the human emissions on climate change in China for the 20th and 21st centuries have been investigated by using multi-model and multi-scenario ensembles. More than 25 CGCMs and scenarios have been employed in this research. To compare with the observations in the 20th century, the multi-model and multi-scenarios ensembles for the surface air temperature and temperature extremes are better than a single model.
The IPCC WG1 2001 report reported on the global warming in the 20th and 21st
centuries as simulated and projected by the many coupled GCMs with human emission
scenarios (Houghton et al., 2001). Our research has focused on the impacts of
the human emissions on the climate changes in China for the 20th and 21st centuries
as simulated and projected by the totality of the available
multi-model and scenario ensemble. More than 25 runs from various climate models and scenarios have been employed and summarized in this research. Here CT represents control run; GG runs with increasing greenhouse gases only and GS runs with greenhouse gases plus sulphate aerosols. Note that the SRES scenarios A1, A2, B1 and B2 were used for the model CCSR/NIES. GCM7 represents the ensemble of CCCGG, CCSR/NIES1-GG, CSIRO-GG, DKRZ-GG, GFDLGG,HADL-GG, NCAR-GG, GCM7-GG, CCC-GS,
CCSR/NIES1-GS, CSIRO-GS, DKRZ-GS, GFDL-GS, HADL-GS, NCAR-GS, GCM7-GS, LASG/IAP1-GG, LASG/IAP2-GG, LASG/IAP2-GS, LASG/IAP2-GS, NCC/IAP T63-GG, NCC/IAP T63-GS, RegCM/CN-GG, RegCM/CN-GS, YONU-GG, CCSR/NIES2 SRES A1, A2, B1, B2. The method of ensembles used takes the simple mathematical mean of all models and scenarios (Luo and Zhao, 1997; Gao et al., 2001; Guo et al., 2001; Zhao and
Xu, 2002; Xu et al., 2002; Ma et al., 2002; Zhao et al., 2003).
2. Changes of the annual surface air temperature in China
Fig. 1 gives the evolutions of surface air temperature in China for the 20th and 21st centuries as simulated and projected by the climate models with the different scenarios. The anomalous correlation coefficients (ACC) of temperature for all models with GG and GS had much larger positive values than those of CT.
For example, the ACC of GCM7 were 0.37 (GG 1900~1999) and 0.74 (GS 1900~1999),
0.65 (GG 1950~1999) and 0.69 (GS 1950~1999), respectively (Table 1). They reached
the 95% significant levels of the confidence. The ranges of ACC of the GCMs
with the different emissions
are 0.07~0.74 for 1900~1999 and 0.26~0.69 for 1950~1999, respectively. The linear trends of the observed temperature in China were 0.39oC/100y for 1900~1999 and 0.78oC/50y for 1950~1999, respectively. The linear trends of the simulated temperature by GCM7 with CT were relatively small. The linear trends of temperature for GCMs with GG overestimated. The linear trends of
temperature for GCMs with GS in both 1900~1999 (0.38oC/100y) and 1950~1999 (0.71oC/50y) were near the observed values, especially for 1900~1999. The investigations also presented the similar situations for the maximum and minimum temperatures in China (Zhao et al., 2003). It means that the combined effects of both greenhouse effects and sulfate aerosols very likely cause the observed warming of the 20th century in China, especially for the last 50 years. It is also noticed in Fig.1, Tables 1 and 2 that results of the multi-model and scenarios ensembles were better than a single model to compare with the observations.
The linear trends of the annual mean temperature change in China for the 21st
century are 4.9 oC/100y and 2.9 oC/100y as projected by the GCM7-GG and GS with
the range 3.0~9.2 oC/100y and -0.3~6.9 oC/100y of all models and scenarios respectively.
It is also noticed that the change of temperature in China for the 21st century
as simulated by the GCM7-GG and GS is greater than the
global and East Asia changes , the linear trends of which were 3.7 oC/100y and 2.7 oC/100y with the ranges of 2.9~7.5 oC/100y and 0.4~5.5 oC/100y respectively.
3. Changes of the annual precipitation in China
Similar to the study of temperature, Fig. 2 shows the evolution of precipitation
in China for the 20th and 21st centuries as simulated and projected by the climate
models with the human emission scenarios. The anomalous correlation coefficients
and linear trends of precipitation changes for the observations and the simulations
by the models did not present any significant relationships (Tables are not
shown). It means that there was no strong evidence and signal to indicate
precipitation change in China for the 20th century caused by the human emissions.
The calculations indicated that the linear trends of the annual precipitation in China for the 21st century are 48~60mm/100y as projected by the multi-model ensembles with a range of -78~185mm/100y by all models.
4. Conclusions and discussions
As summarized in the above sections, the simulations of the surface air temperature and maximum and minimum temperature in China by the multi-model and multiscenarios ensembles are better than a single model to compare with the observations in the 20th century.
Changes in the precipitation over China show no significant trend either in the observations or the models through the 20th century and are relatively small into the 21st century, implying some value in refining the use of the multi-model approach for prediction of future changes in this parameter.
The further research will concentrate on narrowing the uncertainties.
This research was supported by the IPCC-China project and the project on National Report of Climate Change (China). The authors sincerely thank the model groups and the DDC/IPCC for providing their simulations.
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Source: Clivar Exchanges (No. 28 (Vol. 8, No. 4) December 2003)