IPCC Climate Change Data: ECHAM4 B2a Model: 2080 Wind Speed

The ECHAM climate model has been developed from the ECMWF
atmospheric model (therefore the first part of its name: EC) and
a comprehensive parameterisation package developed at Hamburg
therefore the abbreviation HAM) which allows the model to be
used for climate simulations. The model is a spectral transform
model with 19 atmospheric layers and the results used here
derive from experiments performed with spatial resolution T42
(which approximates to about 2.8 degrees longitude/latitude
resolution). The model has also been used at resolutions in the
range T21 to T106. ECHAM4 is the current generation in the line
of ECHAM models (Roeckner, et al., 1992). A summary of
developments regarding model physics in ECHAM4 and a description
of the simulated climate obtained with the uncoupled ECHAM4
model is given in Roeckner et al. (1996). The initial sea
surface temperature and sea-ice data is the COLA/CAC AMIP SST
and sea-ice data set. The mean terrain heights are computed from
high resolution US Navy data set. The fraction of grid area
covered by vegetation based on the Wilson and Henderson-Sellers
(1985) data set. The ocean albedo is a function of solar zenith
angle and the land albedo from the satellite data of Geleyn and
Preuss (1983). A diurnal cycle and gravity wave-drag is
included. The time-step of the model is 24 minutes, except for
radiation which uses two hours. The ocean model is an updated
version of the isopycnal model (OPYC3) developed by Josef
Oberhuber (Oberhuber, 1993) at the Max-Planck-Institute for
Meteorology, Hamburg, Germany. The name OPYC is derived from
Ocean and isoPYCnal co-ordinates. The concept to use isopycnals
as the vertical co-ordinate system for an OGCM is based on the
observation that the interior ocean behaves as a rather
conservative fluid. Even over long distances the origin of water
masses can be traced back by considering the distribution of
active or passive tracers. Treating the ocean as a conservative
fluid fails in areas of significant turbulence activity such as
the surface boundary layer. A surface mixed-layer is therefore
coupled to the interior ocean in order to represent near-surface
vertical mixing and to improve the response time-scales to
atmospheric forcing which is controlled by the mixed-layer
thickness. Since the model is designed for studies on large
scales, a sea ice model with rheology is included and serves the
purpose of de-coupling the ocean from extreme high-latitude
winter conditions and promotes a realistic treatment of the
salinity forcing due to melting or freezing sea ice. The
experiments from which results are used here are the 1000-year
unforced control simulation using the coupled ECHAM4/OPYC3 model
and then two climate change simulations. The greenhouse gas only
forced experiment (referred to as GGa1) used historical
greenhouse gas forcing from 1860 to 1990 followed by a 1 per
cent annum increase in radiative forcing from 1990 to 2099. The
greenhouse gas and sulphate aerosol forced experiment (referred
to as GSa1) used the GGa1 forcing, plus the negative forcing due
to sulphate aerosols. This was represented by means of an
increase in clear-sky surface albedo proportional to the local
sulphate loading. The indirect effects of aerosols were not
simulated. For 1860 to 1990 the historic sulphate aerosol
forcing estimate was used and for 1990 to 2049 the aerosol
forcing estimated for the IS92a emissions scenario. The GSa1
experiment did not extend beyond 2049. Fuller details of the
ECHAM4/OPYC3 coupled model can be found at the DDC Yellow Pages.
Several papers describe results using this version of the model
- see Bacher et al. (1998), Oberhuber et al. (1998), Zhang et
al. (1998). The climate sensitivity of ECHAM4 is about 2.6
degrees C.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 ncreased
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. 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.

ECHAM气候模式脱胎于欧洲中期天气预报中心（ECMWF）大气模式（因此其名称的前半部分为EC）以及汉堡研发的一套综合参数化方案包（因此缩写为HAM），该方案包使得该模式可用于气候模拟。
该模式为谱变换模式，共包含19个大气层，本文所用结果源自空间分辨率为T42的试验（其近似对应约2.8度的经纬度分辨率）。该模式还可在T21至T106的分辨率范围内运行。ECHAM4是ECHAM系列模式的当前正式版本（Roeckner等，1992年）。Roeckner等人1996年的研究总结了ECHAM4的模式物理过程进展，并描述了非耦合ECHAM4模式模拟得到的气候特征。

初始海表温度与海冰数据采用COLA/CAC AMIP海表温度与海冰数据集（Atmospheric Model Intercomparison Project，AMIP）。平均地形高度源自高分辨率美国海军数据集。植被覆盖的格点面积占比基于Wilson与Henderson-Sellers（1985年）的数据集。海洋反照率为太阳天顶角的函数，陆地反照率则取自Geleyn与Preuss（1983年）的卫星观测数据。模式包含日循环与重力波拖曳过程。模式的时间步长为24分钟，辐射过程的时间步长则为2小时。

海洋模式是由德国汉堡马克斯·普朗克气象研究所的Josef Oberhuber开发的等密度层模式（OPYC3）的更新版本（Oberhuber，1993年）。OPYC这一名称源自Ocean（海洋）与isoPYCnal（等密度层）坐标。将等密度层作为海洋环流模式（Ocean General Circulation Model，OGCM）垂直坐标系的理念，基于“海洋内部可被视为相当保守的流体”这一观测事实。即使在长距离范围内，也可通过追踪活性或惰性示踪剂的分布来追溯水团的起源。将海洋视为保守流体的假设在存在显著湍流活动的区域（如表面边界层）并不成立。因此，需将表面混合层与海洋内部耦合，以表征近表层垂直混合过程，并改善由混合层厚度控制的、对大气强迫的响应时间尺度。

由于该模式旨在用于大尺度研究，因此引入了具备流变学特性的海冰模式，其作用是将海洋与高纬度冬季极端条件解耦，并更真实地处理由海冰融化或冻结引起的盐度强迫。

本文所用结果来自两类试验：一是使用耦合ECHAM4/OPYC3模式开展的1000年非强迫控制模拟，二是两项气候变化模拟。仅考虑温室气体强迫的试验（记为“GGa1”）采用了1860年至1990年的历史温室气体强迫，随后自1990年至2099年以每年1%的速率增加辐射强迫。同时考虑温室气体与硫酸盐气溶胶强迫的试验（记为“GSa1”）在“GGa1”强迫的基础上，叠加了硫酸盐气溶胶产生的负强迫，其通过将晴空地表反照率增加至与局地硫酸盐载荷成正比的水平来实现。气溶胶的间接效应未被模拟。1860年至1990年采用历史硫酸盐气溶胶强迫估算值，1990年至2049年采用针对IS92a排放情景的气溶胶强迫估算值。“GSa1”试验的模拟时长未超过2049年。

关于ECHAM4/OPYC3耦合模式的更详细信息可查阅DDC黄页。已有多篇文献使用该版本模式开展研究并发表结果，详见Bacher等（1998年）、Oberhuber等（1998年）以及Zhang等（1998年）。ECHAM4的气候敏感性约为2.6摄氏度。

### A2情景
A2情景下的世界整合为一系列大致以大陆为界的经济区域，强调本地文化根源。部分区域内，宗教参与度的提升使得许多人摒弃物质主义路径，转而专注于为本地社区做贡献。在其他区域，趋势则转向增加教育与科研投入，以及提升经济生产力。社会与政治结构呈现多样化：部分区域建立起更完善的福利体系，收入不平等程度降低；而另一些区域则走向“小政府”模式。环境议题的受重视程度相对较低，尽管部分区域会关注本地污染治理与维护本地环境宜居性。

### B2情景
与B1情景类似，B2情景的世界同样愈发关注环境与社会可持续性，但其特征存在显著差异。教育与福利项目得到广泛推行，推动了死亡率下降，生育率也在一定程度上降低。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，全球经济规模或将达到约250万亿美元。国际间的收入差距有所缩小，但缩小速度慢于全球收敛程度更高的情景（如A1、B1）。通过构建更完善的社区支持网络，本地的不平等程度得到显著缓解。

总体而言，较高的教育水平同时推动了发展与环境保护。事实上，环境保护已是少数几项真正具有全球优先级的议题之一。然而，应对全球环境挑战的战略相较于B1情景成效更弱，因为各国政府难以设计并推行兼顾环境保护与共同经济利益的协议。

B2情景的叙事线尤其有利于社区倡议与社会创新，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，且创新在区域间的异质性更强。全球范围内，研发（Research and Development，R&D）投入延续了当前的下降趋势，国际技术与专业知识的传播机制也弱于A1与B1情景（但强于A2情景）。部分经济快速发展但自然资源有限的区域尤为重视技术研发与双边合作，因此技术变革的分布并不均衡。GDP的能源强度以每年约1%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的整合度更高。城市与交通基础设施是社区创新的重点领域，这有助于降低对私家车的依赖程度，减少城市无序扩张。强调粮食自给自足推动了饮食结构向本地产品转变，人口密度较高的国家肉类消费量有所下降。

能源系统因区域自然资源禀赋的差异而各不相同。提升能源与其他资源利用效率的需求，推动了部分区域开发低碳排放技术。区域层面的环境政策合作在治理部分跨界环境问题上取得了成效，例如由二氧化硫（SO₂）导致的酸雨，这尤其有助于维持农业生产的区域自给能力。区域合作还降低了氮氧化物（Nitrogen Oxides，NOₓ）与挥发性有机化合物（Volatile Organic Compounds，VOCs）的排放量，减少了对流层臭氧浓度升高的发生概率。尽管到2100年全球能源系统仍以烃类燃料为主导，但世界能源供应中化石资源的占比正逐步降低，碳强度也相应下降。