IPCC Climate Change Data: NIES99 A2a Model: 2020 Precipitation

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洋-大气模式（coupled ocean-atmosphere model），由CCSR/NIES大气全球环流模式（Global Circulation Model, GCM）、CCSR海洋全球环流模式、热力学海冰模式与河道径流模式组成（Abe-Ouchi等，1996）。大气部分采用T21谱截断（约5.6度经纬度分辨率）与20个垂直层数；海洋部分采用约2.8度水平网格与17个垂直层数。为抑制模拟气候的漂移，采用大气-海洋间热量与水汽交换的通量调整方案。大气模式采用基于k分布的双流离散纵标法（DOM）辐射方案（Nakajima与Tanaka，1986），该方案可一致性处理气体、云系与气溶胶粒子的吸收、发射与散射过程。在硫酸盐气溶胶光学特性计算中，假设干燥环境下硫酸盐粒子的体积模态半径为0.2微米；硫酸盐的吸湿增长采用d'Almeida等（1991）的经验拟合公式。硫酸盐气溶胶的垂直分布假设在大气低层2 km内保持恒定。温室气体浓度以等效二氧化碳（equivalent-CO2）表征。

共开展3组时长为200个模式年（1890-2090）的积分试验。对照组（CTL）中，全球均匀分布的温室气体浓度固定为345 ppmv 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，硫酸盐浓度保持为0。GS试验中，同时考虑人为硫酸盐与温室气体的增加，气溶胶散射（气溶胶直接效应）按前述方式显式表征，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参考Mitchell与Johns（1997）的方案。温室气体浓度变化基于1890-1990年的历史记录，1990年后以每年1%的复合速率增长。对于硫酸盐气溶胶，以1986年与2050年的硫酸盐载荷地理分布（由硫循环模式Langer与Rodhe，1991估算得到）作为基准分布。基于全球年平均硫排放速率，对1990年前的年份采用1986年基准分布进行尺度缩放，2050年后的年份采用2050年基准分布进行尺度缩放，中间年份通过两个基准分布插值得到逐时段的分布时间序列。未来硫排放速率基于IPCC IS92a情景。本试验中硫酸盐浓度初始设置为1890年时为0，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）。由平衡积分得到的CCSR/NIES模式气候敏感度估算为3.5摄氏度。以下为CCSR/NIES模式的全球平均温度、降水与CO₂变化（相对于1961-1990年基准期）。

就A2排放情景而言，其核心特征为区域与本土文化的强化，诸多地区回归家庭价值观念。A2情景下的世界逐步整合为一系列以大陆为单元的经济区域，强调本土文化根源。部分地区宗教参与度提升，促使民众摒弃物质主义路径，转而投身本地社区建设；其余地区则倾向于加大教育与科研投入，推动经济生产率增长。社会与政治结构趋于多元：部分地区建立更完善的福利体系，缩小收入差距；其余地区则推行“精简型”政府。环境关注度相对较低，仅部分地区着力管控本地污染、维护本土环境宜居性。

相较于A1与B1情景，A2情景下国际紧张局势更多，合作更少。人员、思想与资本流动性更弱，技术扩散速率缓慢。生产率进而人均收入的国际差距保持甚至扩大。由于侧重家庭与社区生活，尽管各地区生育率存在差异，但整体下降速率缓慢。因此，该情景家族的人口增长较高（至2100年达150亿），相较于A1与B1情景世界人均收入更低，2050年人均收入约为7200美元，2100年约为16000美元。

部分地区技术变革迅速，部分地区则较为缓慢，产业结构适配本地资源禀赋、文化与教育水平。能源与矿产资源丰富的地区发展资源密集型经济；资源匮乏地区则高度优先通过技术创新降低进口依赖，提升资源利用效率并开发替代投入品。不同地区的燃料结构主要由资源可获得性决定。地区间技术路径分化持续存在：高收入但资源匮乏的地区转向先进的后化石燃料技术（土地资源丰富地区发展可再生能源，人口密集、资源匮乏地区发展核电）；低收入且资源丰富的地区则普遍依赖传统化石燃料技术。

由于存在大量粮食需求，农业生产率是该未来场景下创新与研发（R&D）工作的核心聚焦领域之一。初始阶段严重的土壤侵蚀与水污染问题，最终通过本地发展可持续高产农业得到缓解。

尽管部分地区关注本地与区域潜在环境损害，但环境政策的实施并不均衡。例如，亚洲地区因考虑到对人类健康与农业生产的影响，减少了硫与颗粒物排放；而非洲地区则因加大煤炭与其他矿产资源开发力度，相关排放有所增加。A2情景世界的能源与碳强度较高，对应温室气体排放量也较高，其二氧化碳排放量为四类情景家族中最高。