IPCC Climate Change Data: CSIRO B2a Model: 2050 Maximum Temperature

The CSIRO Atmospheric Research Mark 2b climate model (Hirst
et al., 1996, 1999) has recently been used for a number of more
sophisticated climate change simulations. These start from 1880
to avoid the "cold start problem". This version of
the CSIRO model includes the Gent-McWilliams mixing scheme in
the ocean and shows greatly reduced climate drift relative to
earlier versions (e.g. Dix and Hunt, 1998). The drift in global
mean surface temperature in the new control run is about -0.02
degrees C/century. Note that the model uses flux correction.
The model atmosphere has 9 levels in the vertical and horizontal
resolution of spectral R21 (approximately 5.6 by 3.2 degrees).
The ocean model has the same horizontal resolution with 21
levels. The equilibrium sensitivity to doubled CO2 of a mixed
layer ocean version of the model is 4.3 degrees. This is at the
high end of the range of model sensitivities (e.g. IPCC 1995,
Table 6.3). In the basic greenhouse gas experiment the model
combines the effect of all radiatively active trace gases into
an "equivalent" CO2 concentration. Observed
concentrations are used from 1880 to 1990 and the IS92a
projections into the future. This gives close to a 1%/year
compounding increase of equivalent CO2. Another model
experiment includes the negative radiative forcing from
atmospheric sulphate aerosol. The direct aerosol forcing is
included via a perturbation of the surface albedo, similarly to
the Hadley Centre experiments described by Mitchell et al (1995)
and Mitchell and Johns (1997) . The sulphate concentrations are
the same as used in the Hadley Centre experiments. However the
chosen aerosol optical properties are different, giving a
present day forcing due to anthropogenic sulphate of about -0.4
W/m^2. This can be compared to the 1880-1990 greenhouse gas
forcing of about 2 W/m^2. The magnitude of the 20th century
warming in the model including aerosol matches the observed
reasonably well. However there are a number of forcings missing
from the model, including solar variability, sulphate indirect
effect and the effect of soot. The climate sensitivity of
CSIRO-Mk2 is about 4.3 degrees C (Watterson et al.,1997). Like B1, the B2 world is one of increased concern for
environmental and social sustainability, but the character of
this world differs substantially. Education and welfare
programs are widely pursued leading to reductions in mortality
and, to a lesser extent, fertility. The population reaches about
10 billion people by 2100, consistent with both the United
Nations and IIASA median projections. Income per capita grows at
an intermediary rate to reach about US$12,000 by 2050. By 2100
the global economy might expand to reach some US$250 trillion.
International income differences decrease, although not as
rapidly as in scenarios of higher global convergence (A1, B1).
Local inequity is reduced considerably through the development
of stronger community support networks. Generally high
educational levels promote both development and environmental
protection. Indeed, environmental protection is one of the few
remaining truly international priorities. However, strategies to
address global environmental challenges are less successful than
in B1, as governments have difficulty designing and implementing
agreements that combine environmental protection with mutual
economic benefits. The B2 storyline presents a particularly
favorable climate for community initiative and social
innovation, especially in view of high educational levels.
Technological frontiers are pushed less than in A1 and B1 and
innovations are also regionally more heterogeneous. Globally,
investment in R and D continues its current declining trend, and
mechanisms for international diffusion of technology and
know-how remain weaker than in scenarios A1 and B1 (but higher
than in scenario A2). Some regions with rapid economic
development and limited natural resources place particular
emphasis on technology development and bilateral co-operation.
Technical change is therefore uneven. The energy intensity of
GDP declines at about one percent per year, in line with the
average historical experience of the last two centuries.
Land-use management becomes better integrated at the local level
in the B2 world. Urban and transport infrastructure is a
particular focus of community innovation, contributing to a low
level of car dependence and less urban sprawl. An emphasis on
food self-reliance contributes to a shift in dietary patterns
towards local products, with reduced meat consumption in
countries with high population densities. Energy systems differ
from region to region, depending on the availability of natural
resources. The need to use energy and other resources more
efficiently spurs the development of less carbon-intensive
technology in some regions. Environment policy cooperation at
the regional level leads to success in the management of some
transboundary environmental problems, such as acidification due
to SO2, especially to sustain regional self-reliance in
agricultural production. Regional cooperation also results in
lower emissions of NOx and VOCs, reducing the incidence of
elevated tropospheric ozone levels. Although globally the energy
system remains predominantly hydrocarbon-based to 2100, there is
a gradual transition away from the current share of fossil
resources in world energy supply, with a corresponding reduction
in carbon intensity.

澳大利亚联邦科学与工业研究组织（Commonwealth Scientific and Industrial Research Organisation, CSIRO）大气研究部Mark 2b型气候模式（Hirst等，1996、1999）近期被应用于多项更为复杂的气候变化模拟试验。该类试验始于1880年，以规避冷启动问题（cold start problem）。此版本的CSIRO气候模式在海洋模块中引入了Gent-McWilliams混合方案（Gent-McWilliams mixing scheme），相较于早期版本（如Dix与Hunt，1998），其气候漂移现象已大幅缓解。新控制试验中，全球平均地表温度的漂移速率约为-0.02℃/世纪。需注意，该模式采用了通量校正（flux correction）方案。模式大气的垂直层数为9层，谱截断水平分辨率为R21（约5.6×3.2个经度/纬度度）。海洋模块与大气模块具有相同的水平分辨率，垂直层数为21层。该模式混合层海洋版本对CO₂倍增（doubled CO₂）的平衡敏感度为4.3℃，处于气候模式敏感度区间的上限（如政府间气候变化专门委员会（Intergovernmental Panel on Climate Change, IPCC）1995年报告表6.3）。
在基础温室气体试验中，模式将所有辐射活性痕量气体（radiatively active trace gases）的效应整合为等效CO₂浓度（equivalent CO₂ concentration）。1880年至1990年采用观测浓度，未来时段则采用IS92a情景预测值，由此实现等效CO₂浓度以约1%/年的速率复合增长。另一项模式试验纳入了大气硫酸盐气溶胶（atmospheric sulphate aerosol）产生的负辐射强迫（negative radiative forcing）。直接气溶胶强迫通过地表反照率（surface albedo）扰动实现，其原理与Mitchell等（1995）及Mitchell与Johns（1997）描述的哈德利中心（Hadley Centre）试验一致。硫酸盐气溶胶浓度的设置与哈德利中心试验完全相同，但所选气溶胶光学特性存在差异，由此得到当前人为硫酸盐气溶胶产生的辐射强迫约为-0.4 W/m²，可与1880年至1990年温室气体产生的约2 W/m²辐射强迫进行对比。纳入气溶胶强迫的模式对20世纪变暖的模拟结果与观测值较为吻合，但该模式仍缺失多项强迫因子，包括太阳活动变化（solar variability）、硫酸盐间接效应（sulphate indirect effect）以及黑碳（soot）的影响。CSIRO-Mk2型模式的气候敏感度约为4.3℃（Watterson等，1997）。
与B1情景类似，B2情景同样将提升环境与社会可持续性作为核心关切，但二者的情景特征存在显著差异。该情景下，教育与福利项目得到广泛推行，推动了死亡率下降，并在一定程度上降低了生育率。到2100年，全球人口将达到约100亿，与联合国及国际应用系统分析研究所（International Institute for Applied Systems Analysis, IIASA）的中位数预测结果一致。人均收入以中等速率增长，到2050年将达到约12000美元；到2100年，全球经济总量有望达到约250万亿美元。国际收入差距有所缩小，但缩小速度慢于全球趋同程度更高的A1、B1情景。通过构建更完善的社区支持网络，本地不平等程度得到显著缓解。
普遍较高的教育水平同时促进了经济发展与环境保护，事实上，环境保护已是少数几项真正具有全球意义的优先议题之一。然而，应对全球环境挑战的战略成效不及B1情景，原因在于各国政府难以设计并推行兼顾环境保护与共同经济收益的国际协定。B2情景尤其有利于社区自主行动与社会创新，尤其是在教育水平较高的背景下。技术前沿的推进速度慢于A1与B1情景，且创新在区域间分布更为不均。全球范围内，研发（Research and Development, R&D）投入持续维持当前的下降趋势，技术与专业知识的国际扩散机制仍弱于A1、B1情景（但强于A2情景）。部分经济快速发展但自然资源匮乏的地区尤为重视技术研发与双边合作，因此技术进步存在显著的区域不均衡性。GDP（国内生产总值，Gross Domestic Product）能源强度以约1%/年的速率下降，与过去两个世纪的平均历史经验相符。
在B2情景的世界中，土地利用管理在地方层面得到更有效的整合。城市与交通基础设施建设是社区创新的重点领域，有助于降低对私家车的依赖并缓解城市蔓延。强调粮食自给自足推动了饮食结构向本地产品转型，在人口密度较高的国家，肉类消费有所减少。能源系统因自然资源禀赋的差异而存在区域差异。提高能源与其他资源利用效率的需求，推动部分地区开发低碳排放技术。区域层面的环境政策合作在部分跨边界环境问题治理中取得了成效，例如二氧化硫导致的酸化问题，这尤其有助于维持区域农业生产的自给能力。区域合作还降低了氮氧化物（NOₓ）与挥发性有机化合物（VOCs）的排放，减少了对流层臭氧浓度超标事件的发生。尽管到2100年全球能源系统仍将以碳氢化合物为主体，但世界能源供应中化石资源的占比正逐步降低，碳强度也随之下降。