Influence of CO_2 Doubling on Water Transport Process at Root/Soil Interface of Pinus sylvestris var. sylvestriformis Seedlings

Water transport at the root/soil interface of 1 year old Pinus sylvestris Linn. var. sylvestriformis (Takenouchi) Cheng et C. D. Chu seedlings under CO 2 doubling was studied by measuring soil electric conductance to survey soil water profiles and comparing it with root distribution surveyed by soil coring and root harvesting in Changbai Mountain in 1999. The results were: (1) The profiles of soil water content were adjusted by root activity. The water content of the soil layer with abundant roots was higher. (2) When CO 2 concentration was doubled, water transport was more active at the root/soil interface and the roots were distributed into deeper layer. It was shown in this work that the method of measuring electric conductance is an inexpensive, non_destructive and relatively sensitive way for underground water transport process.

Multi-model Projection of July–August Climate Extreme Changes over China under CO_2 Doubling. Part I: Precipitation

Potential changes in precipitation extremes in July–August over China in response to CO 2 doubling are analyzed based on the output of 24 coupled climate models from the Twentieth-Century Climate in Coupled Models （20C3M） experiment and the 1% per year CO 2 increase experiment （to doubling） （1pctto2x） of phase 3 of the Coupled Model Inter-comparison Project （CMIP3）. Evaluation of the models’ performance in simulating the mean state shows that the majority of models fairly reproduce the broad spatial pattern of observed precipitation. However, all the models underestimate extreme precipitation by ～50%. The spread among the models over the Tibetan Plateau is ～2–3 times larger than that over the other areas. Models with higher resolution generally perform better than those with lower resolutions in terms of spatial pattern and precipitation amount. Under the 1pctto2x scenario, the ratio between the absolute value of MME extreme precipitation change and model spread is larger than that of total precipitation, indicating a relatively robust change of extremes. The change of extreme precipitation is more homogeneous than the total precipitation. Analysis on the output of Geophysical Fluid Dynamics Laboratory coupled climate model version 2.1 （GFDL-CM2.1） indicates that the spatially consistent increase of surface temperature and water vapor content contribute to the large increase of extreme precipitation over contiguous China, which follows the Clausius–Clapeyron relationship. Whereas, the meridionally tri-polar pattern of mean precipitation change over eastern China is dominated by the change of water vapor convergence, which is determined by the response of monsoon circulation to global warming.

Multi-Model Projection of July–August Climate Extreme Changes over China under CO_2 Doubling. Part II: Temperature

This is the second part of the authors’ analysis on the output of 24 coupled climate models from the Twentieth-Century Climate in Coupled Models （20C3M） experiment and 1% per year CO 2 increase experiment （to doubling） （1pctto2x） of phase 3 of the Coupled Model Inter-comparison Project （CMIP3）. The study focuses on the potential changes of July–August temperature extremes over China. The pattern correlation coefficients of the simulated temperature with the observations are 0.6–0.9, which are higher than the results for precipitation. However, most models have cold bias compared to observation, with a larger cold bias over western China （5°C） than over eastern China （2°C）. The multi-model ensemble （MME） exhibits a significant increase of temperature under the 1pctto2x scenario. The amplitude of the MME warming shows a northwest–southeast decreasing gradient. The warming spread among the models （～1°C– 2°C） is less than MME warming （～2°C–4°C）, indicating a relatively robust temperature change under CO 2 doubling. Further analysis of Geophysical Fluid Dynamics Laboratory coupled climate model version 2.1 （GFDL-CM2.1） simulations suggests that the warming pattern may be related to heat transport by summer monsoons. The contrast of cloud effects also has contributions. The different vertical structures of warming over northwestern China and southeastern China may be attributed to the different natures of vertical circulations. The deep, moist convection over southeastern China is an effective mechanism for ＂transporting＂ the warming upward, leading to more upper-level warming. In northwestern China, the warming is more surface-orientated, possibly due to the shallow, dry convection.

Response of Asian Summer Monsoon to CO_2 Doubling

Based on simulations of the IPCC 20C3M and SRES A1B experiments in ten coupled models, the Asian summer mon-soon (ASM) response to CO2 doubling and the different responses among models are examined. Nine models show the similar results that the weakening of land-ocean thermal contrast caused by the CO2 doubling contributes to a weaker large-scale ASM circulation. Further analysis in this study also shows that the major ASM components,such as the Somali cross-equatorial flow,the low level India-South China Sea monsoon trough,and the upper level tropical easterly jet stream, weaken as CO2 doubles.However,the ASM rainfall increases as a result of the increased moisture from the warmer Indian Ocean and the South China Sea, and the enhanced northward moisture transport over the ASM region.For the response of enhanced northward moisture transport over South Asia, the positive contribution of moisture content increase in the Indian Ocean is dominant and the negative contribution of the weaker mon-soon circulation is secondary at 850 hPa,but both have positive contribution to the total moisture transport along the East China coast.The paradox of the weaker ASM circulation and the increasing precipitation in CO2 doubling is confirmed.It is found that strengthening of northward moisture transport could intensify the precipitation and atmospheric heat source over the north Arabian Sea and East China,and result in enhanced southwesterly at 850 hPa as global warming occurs.All ten models show significant enhanced southwesterly response over the north Arabian Sea,and six of them show enhanced southwesterly response along the East China coast.

Fractal analysis for root growth of plant seedlings under doubled CO_2 concentration

Fractal geometry was applied and box dimension was used as an indicator to analyze the effects of doubled CO\-2 concentration on the root growth of plant seedlings. Results showed that doubled CO\-2 concentration displayed different effects on root branching characteristics of C\-3 and C\-4 plants. There was an obvious increase of root branches in spring wheat while there were no significant effects on roots of sweet sorghum. In different soil layers, root branching of spring wheat was stimulated and this promotion was most significant in the second layer (10-20 cm), which denoted that elevated CO\-2 altered the root branching pattern. That means higher CO 2 concentration influences not only root growth but also its differentiation and development.

Influences of greenhouse effect on agricultural production in China

An obvious warming in China induced by doubled carbon, dioxide as simulated by the climatic models have been found. It is also noticed that there might be drying or wetting in some parts of China induced by doubled CO2 as simulated by the general circulation models(GCMs). Agricultural productivity mainly depends on the temperature, rainfall and soil moisture in China. The changes of agricultural productivity in the different parts of China induced by doubled CO2 have been estimated in this paper. It is shown that the greenhouse effect might cause increasing production in some parts of China and decreasing production in other parts of China.