IPCC Climate Change Data: NIES99 A2a Model: 2050 Minimum Temperature

The model used here is a coupled ocean-atmosphere model that
consists of the CCSR/NIES atmospheric GCM, the CCSR ocean GCM, a
thermodynamic sea-ice model, and a river routing model
(Abe-Ouchi et al., 1996). The spatial resolution is T21 spectral
truncation (roughly 5.6 degrees latitude/longitude) and 20
vertical levels for the atmospheric part, and roughly 2.8
degrees horizontal grid and 17 vertical levels for the oceanic
part. Flux adjustment for atmosphere-ocean heat and water
exchange is applied to prevent a drift of the modelled climate.
The atmospheric model adopts a radiation scheme based on the
k-distribution, two-stream discrete ordinate method (DOM)
(Nakajima and Tanaka, 1986). This scheme can deal with
absorption, emission and scattering by gases, clouds and aerosol
particles in a consistent manner. In the calculation of sulphate
aerosol optical properties, the volumetric mode radius of the
sulphate particle in dry environment is assumed to be 0.2
micron. The hygroscopic growth of the sulphate is considered by
an empirical fit of d'Almeida et al. (1991). The vertical
distribution of the sulphate aerosol is assumed to be constant
in the lowest 2 km of the atmosphere. The concentrations of
greenhouse gases are represented by equivalent-CO2. Three
integrations are made for 200 model years (1890-2090). In the
control experiment (CTL), the globally uniform concentration of
greenhouse gases is kept constant at 345 ppmv CO2-equivalent and
the concentration of sulphate is set to zero. In the experiment
GG, the concentration of greenhouse gases is gradually
increased, while that of sulphate is set to zero. In the
experiments GS, the increase in anthropogenic sulphate as well
as that in greenhouse gases is given and the aerosol scattering
(the direct effect of aerosol) is explicitly represented in the
way described above. The indirect effect of aerosol is not
included in any experiment. The scenario of atmospheric
concentrations of greenhouse gases and sulphate aerosols is
given in accordance with Mitchell and Johns (1997). The increase
in greenhouse gases is based on the historical record from 1890
to 1990 and is increased by 1 percent / yr (compound) after
1990. For sulphate aerosols, geographical distributions of
sulphate loading for 1986 and 2050, which are estimated by a
sulphur cycle model (Langer and Rodhe, 1991), are used as basic
patterns. Based on global and annual mean sulphur emission
rates, the 1986 pattern is scaled for years before 1990; the
2050 pattern is scaled for years after 2050; and the pattern is
interpolated from the two basic ones for intermediate years to
give the time series of the distribution. The sulphur emission
rate in the future is based on the IPCC IS92a scenario. The
sulphate concentration is offset in our run so that it starts
from zero at 1890. The seasonal variation of sulphate
concentration is ignored. Discussion on the results of the
experiments will be found in Emori et al. (1999). Climate
sensitivity of the CCSR/NIES model derived by equilibrium runs
is estimated to be 3.5 degrees Celsius. Global-Mean Temperature,
Precipitation and CO2 Changes (w.r.t. 1961-90) for the CCSR/NIES model. For the A2 emissions scenario the main emphasis is on a
strengthening of regional and local culture, with a "return
to family values" in many regions. The A2 world
"consolidates" into a series of roughly continental
economic regions, emphasizing local cultural roots. In some
regions, increased religious participation leads many to reject
a materialist path and to focus attention on contributing to the
local community. Elsewhere, the trend is towards increased
investment in education and science and growth in economic
productivity. Social and political structures diversify, with
some regions moving towards stronger welfare systems and reduced
income inequality, while others move towards "lean"
government. Environmental concerns are relatively weak, although
some attention is paid to bringing local pollution under control
and maintaining local environmental amenities. The A2 world
sees more international tensions and less cooperation than in A1
or B1. People, ideas and capital are less mobile so that
technology diffuses slowly. International disparities in
productivity, and hence income per capita, are maintained or
increased. With the emphasis on family and community life,
fertility rates decline only slowly, although they vary among
regions. Hence, this scenario family has high population growth
(to 15 billion by 2100) with comparatively low incomes per
capita relative to the A1 and B1 worlds, at US$7,200 in 2050 and
US$16,000 in 2100. Technological change is rapid in some
regions and slow in others as industry adjusts to local resource
endowments, culture, and education levels. Regions with abundant
energy and mineral resources evolve more resource intensive
economies, while those poor in resources place very high
priority on minimizing import dependence through technological
innovation to improve resource efficiency and make use of
substitute inputs. The fuel mix in different regions is
determined primarily by resource availability. And divisions
among regions persist in terms of their mix of technologies,
with high-income but resource-poor regions shifting toward
advanced post fossil technologies (renewables in regions of
large land availability, nuclear in densely populated, resource
poor regions) and low-income resource-rich regions generally
relying on older fossil technologies. With substantial food
requirements, agricultural productivity is one of the main focus
areas for innovation and RD efforts in this future. Initially
high levels of soil erosion and water pollution are eventually
eased through the local development of more sustainable
high-yield agriculture. Although attention is given to
potential local and regional environmental damage, it is not
uniform across regions. For example, sulfur and particulate
emissions are reduced in Asia due to impacts on human health and
agricultural production but increase in Africa as a result of
the intensified exploitation of coal and other mineral
resources. The A2 world sees high energy and carbon intensity,
and correspondingly high GHG emissions. Its CO2 emissions are
the highest of all four scenario families.

本研究采用的模式为耦合海气模式，由CCSR/NIES大气环流模式（General Circulation Model，GCM）、CCSR海洋环流模式（GCM）、热力学海冰模式以及河道汇流模式组成（Abe-Ouchi等，1996）。大气部分的空间分辨率采用T21谱截断（约5.6度经/纬度），垂直层数为20层；海洋部分的水平网格分辨率约为2.8度，垂直层数为17层。为抑制模拟气候的漂移，本研究对海气间的热量与水汽交换进行了通量调整。

大气模式采用基于k分布的双流离散纵标法（Discrete Ordinate Method，DOM）辐射方案（Nakajima与Tanaka，1986）。该方案可统一处理气体、云系及气溶胶粒子的吸收、发射与散射过程。在硫酸盐气溶胶光学特性计算中，假设干环境下硫酸盐粒子的体积模态半径为0.2微米。硫酸盐的吸湿增长特性采用d'Almeida等（1991）提出的经验拟合公式进行表征。假设硫酸盐气溶胶在大气低层2公里范围内的垂直分布保持恒定。温室气体浓度以二氧化碳当量（equivalent-CO₂）表征。

本研究共开展3组积分试验，积分时长为200个模式年（1890-2090年）。对照组试验（CTL）中，全球均匀分布的温室气体浓度固定为345ppmv二氧化碳当量，硫酸盐浓度设为0。GG试验中，温室气体浓度逐步升高，硫酸盐浓度则维持为0。GS试验中，人为源硫酸盐与温室气体浓度均随时间变化，且气溶胶散射（气溶胶直接效应）采用前文所述方式进行显式表征。所有试验均未考虑气溶胶间接效应。

温室气体与硫酸盐气溶胶的大气浓度情景设置参考Mitchell与Johns（1997）的研究方案。温室气体浓度变化以1890-1990年的历史观测数据为基准，1990年后以每年1%的复合增长率递增。对于硫酸盐气溶胶，采用硫循环模式（Langer与Rodhe，1991）估算得到的1986年与2050年硫酸盐负荷空间分布作为基准情景。基于全球年均硫排放速率，1986年基准情景用于1990年前的模拟；2050年基准情景用于2050年后的模拟；中间年份的分布则通过对两个基准情景进行插值得到，从而构建浓度分布的时间序列。未来硫排放速率参考政府间气候变化专门委员会（Intergovernmental Panel on Climate Change，IPCC）的IS92a情景设置。本试验中硫酸盐浓度经过偏移校正，确保1890年时初始浓度为0。模拟中未考虑硫酸盐浓度的季节变化。

相关试验结果的讨论详见Emori等（1999）的研究。通过平衡态模拟得到的CCSR/NIES模式气候敏感度约为3.5摄氏度。本部分为CCSR/NIES模式的全球平均温度、降水及二氧化碳变化（相对于1961-1990年基准期）。

A2排放情景的核心特征为强化区域与本土文化，诸多地区呈现“回归家庭价值观”的趋势。该情景下的世界将整合为若干大致以大陆为界的经济区域，同时凸显本土文化根源。部分地区宗教参与度提升，使得多数民众摒弃物质主义发展路径，转而专注于为本地社区做贡献。其他地区则倾向于加大教育与科研投入，推动经济生产率提升。社会与政治结构呈现多元化特征：部分地区建立更为完善的福利体系，缩小收入差距；而部分地区则推行“精简型”政府治理模式。尽管部分地区会关注本地污染治理与生态环境维护，但整体环境议题的受重视程度相对较低。

A2情景下的国际紧张局势较A1与B1情景更为突出，国际合作则相对匮乏。人员、思想与资本的流动性减弱，导致技术传播速度放缓。各国生产率进而人均收入的国际差距将持续存在甚至进一步扩大。由于侧重家庭与社区生活，尽管各地区生育率存在差异，但整体下降速度缓慢。因此，该情景下人口增长较快（至2100年达到150亿），人均收入水平相对A1与B1情景偏低：2050年人均收入为7200美元，2100年为16000美元。

部分地区技术变革速度较快，部分地区则较慢，这是由于各地区工业发展需适配本地资源禀赋、文化传统与教育水平。能源与矿产资源丰富的地区将发展资源密集型经济；而资源匮乏的地区则将通过技术创新提升资源利用效率、开发替代投入品作为优先方向，以降低对资源进口的依赖。各地区的能源结构主要由资源禀赋决定。地区间的技术结构分化将持续存在：高收入但资源匮乏的地区将转向先进的后化石能源技术（土地充足地区发展可再生能源，人口密集且资源匮乏地区发展核电）；而低收入且资源丰富的地区则普遍依赖传统化石能源技术。

由于粮食需求庞大，农业生产率将成为该未来情景下创新与研发工作的核心方向之一。尽管初期土壤侵蚀与水污染问题较为严重，但通过本地发展可持续高产农业，这些问题将逐步得到缓解。尽管部分地区会关注本地与区域潜在的环境破坏问题，但这种关注存在显著的区域差异。例如，由于意识到硫氧化物与颗粒物排放对人体健康及农业生产的危害，亚洲地区将减少此类排放；而非洲地区则因加大煤炭与其他矿产资源开发力度，导致此类排放增加。

A2情景下的能源与碳强度较高，相应的温室气体排放量也较高，其二氧化碳排放量在四大情景家族中位居首位。