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APN Newsletters |
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Towards Adequate Impact Assessment of Climate Change on Asia
Congbin Fu
Global change is taking place in all aspects of the earth system and affecting great significantly on the human society. Policymakers, resource managers and public need to know what the consequences of global change will be for their regions,and understand the environmental and socio-economic significance of these consequences. Therefore an important long-term goal is the accurate projection of regional climate change, so that potential impacts can be adequately assessed. The current assessment on potential changes in Asia under global warming scenarios have shown that there would be significant changes in Asia in terms of climate, water resources, agriculture as well as the natural vegetation covers in about middle of next century. For instance, when both the greenhouse gas forcing and sulphate aerosol effects are included in the coupled ocean-atmospheric models, the mean temperature for Asia region will be warming about 1.70 C in winter and 2.8 0 C in summer with more warming in North than in South and decreasing precipitation about 0.6mm/day in summer and no significant change in winter. In terms of water resources, the area mean soil moisture might decrease about 0.5 cm in winter and 1.5 cm in summer. The surface runoff might decrease over most of Asia, about 0.5 mm/day on average. The impacts on natural vegetation cover are more significant in middle and higher latitudes than in tropics and subtropics, such as increasing of boreal forest, but decreasing of temperate forest and tropical dry forest. The impacts on agriculture are particularly important for Asia as this region is one the largest crop land over the world. In general, the growing seasons might be extended due to the warming temperature. Taking China as an example, the northern boundary of triple cropping area would shift northward more than 50 latitude and the single cropping area might reduce 23.1% and the triple cropping area might extend 22.4% than present. But the concurrent decreasing of soil moisture might be harmful for crop production. According to the estimation based on 5 GCM's scenarios, the total crop yield might decrease by 10-30% over most of Asia except for some part of China. However, a 4-year top chamber experiment show that the high CO2 concentration would increase the yield for three main crops of northern China Plane, especially the C3 crops ( wheat and soybean), while the quality of the grain would be reduced in terms of the protein constituent. It is recommended that governments of the region will take these research results as a necessary ingredient for their wise policy making in order to maintain the global life-support system need for human survivals. However the current impact assessments were made mainly based on the scenarios simulated by Global Climate Models ( GCMs) and the confidence remains low in the projection of regional climate by present GCMs. For instance, the bias of current GCMs in simulating climate in East Asia can be as high as 200% for precipitation and 120 C for temperature. The estimation of potential changes of crop yield in China form different GCM's scenarios can be in range of -78% to + 15% for rice, -21% to + 55% for wheat and -19% to + 5% for maize. Therefore the scientific evaluation on both the uses and uncertainties of these assessments are particularly necessary before transferring to policy makers and public users. One of the most promising approaches to improve the projection of regional climate change is the development of regional climate model (RCM) which can better capture both the regional forcing and the large scale forcing through nesting with the GCM. In order to develop a regional climate model which will better describe the regional features of Asia monsoon system, a START-APN RCM project is now under implement by multiple funding sources, including several national projects, START and APN supports. The project is named as Regional Modeling the Changes of " General Monsoon System" of Asia Under Anthropogenic Forcing which consists of 7 components: (1) Integrated analysis on the characteristics of environmental changes in Asia monsoon region. (2) Development of a conceptual model of " General Monsoon System " (3) Development of a coupled climate/ecology/chemistry regional model for Asia (4) Development of a data base for regional modeling and diagnosis (5) Simulation of climate change in Asia under regional anthropogenic forcing factors (6) Regional analysis of environmental and socio-economic consequence (7) Integrated assessment study based on regional climate change scenarios. The main recent progress of the project is the development of a concept of " General Monsoon System ", a coupled physical/biological/chemical/social monsoon system. Researches have shown that climate and ecosystem are coupled with each other strongly in the monsoon regions in two way interactions. On one hand, the ecosystems over there are very sensitive in response to the high rate of monsoon climate changes on various time scales, i.e. the seasonal jump, high inter-annual and inter-decadal variability and the abrupt change between climate regimes at longer time scales. The high rate monsoon climate changes serve as the strong driving force for the variation of ecosystem over there. On the other hand, the terrestrial ecosystems over the monsoon region occupy large portion of the global biomass and serves as a huge evapotranspiration source and plays crucial role in the global hydrological cycle and biogeochemical cycle as well. The changes of ecosystem should have significant feedback on monsoon climate. Therefore there is a need to introduce the biological component to couple with the physical monsoon climate. There is also an important regional feature for Asia i.e. Asia is the habitat for nearly 57.2% of the world population and is undergoing rapid economic growth and continue population increase. It stands at one of the most strong human activity areas to force the environmental change. The anthropogenic modification of the monsoon system, due to mainly the industrial emissions, land use/cover changes and urbanization, would occur very likely. Therefore there is a need to introduce the human component to couple with the natural monsoon system. When the above anthropogenic forcing is taken into account, the chemical process also involves the monsoon system. There is the need to introduce the chemical component to couple with the physical monsoon climate too. It is anticipated that from global change point view, a more completed monsoon system should be a physical/biological/chemical/social coupled system. This is what can be called "the General Monsoon System". Since current regional climate models are not able to describe these major processes of the Asia monsoon system, it is necessary to develop a regional climate model for Asia in conjunction with that of GCMs to meet the needs to improve the impact assessment of climate change on Asia. As a first step, the development of two major components of this model , climate-vegetation coupling and climate-aerosol coupling which very likely are enhanced through regional anthropogenic forcing in Asia ( i.e. land use/cover change and industrial emissions ) is now undertaking in this START/TEACOM-APN project. The results of application of this new version of RCM for East Asia has shown how this will help to improve the impact assessment of climate change in Asia. For example, the troposphere aerosols resulting from combustion of fossil fuels, biomass burning and other anthropogenic sources have led to a negative direct forcing as high as -1.7 WM-2 in East Asia, while it is about - 0.5 WM-2 on global average. The negative radiative forcing over East Asia is the same order of direct positive forcing of CO2 on global average ( 1.5 WM-2 ). At present there very few projections of climate change with coupled atmospheric -ocean models which include the radiative effects of aerosols. Those that have been run include a very simplified representation of aerosol effects. To study the effects of industrial sulphate aerosols on Asia monsoon system, a new radiation scheme which includes the sulphate aerosols is developed and coupled with the regional climate through a transport model. The numerical experiments which include both direct and indirect effects of aerosols over East Asia have shown a significant cooling over the southern part of Temperate East Asia, a pattern similar to the observed temperature changes in last 30 years. This regional pattern has not captured by the most of GCMs. These preliminary results indicate the possible application of new version of RCM for Asia for the improvement of impact assessment. Some numerical experiments of the effects of land use/cover change on Asia monsoon system have also shown the possible application by introducing the biological component in projection of monsoon climate changes.
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