IPCC Climate Change Data: HADCM3 A2b Model: 2080 Precipitation

The recent experiments performed at the Hadley Centre have
used the new Unified Model (Cullen, 1993). These experiments
represent a large step forward in the way climate change is
modelled by GCMs and raises new possibilities for scenario
construction. This experiment has overcome some of the major
difficulties that were associated with the previous generations
of equilibrium (circa IPCC 1990) and cold-start transient (circa
IPCC 1992) climate change experiments. HadCM2 has a spatial
resolution of 2.5 degrees x 3.75 degrees (latitude by longitude)
and the representation produces a grid box resolution of 96 x 73
grid cells. This produces a surface spatial resolution of about
417km x 278 km reducing to 295 x 278km at 45 degrees North and
South (comparable to a spectral resolution of T42). The
equilibrium climate sensitivity (DT2x) of HadCM2, that is the
global-mean temperature response to a doubling of effective CO2
concentration, is approximately 2.5 degrees C, although, this
quantity varies with the time-scale considered. This is somewhat
lower than most other GCMs (IPCC, 1992). In order to undertake a
'warm-start' experiment it is necessary to perturb the model
with a forcing from an early historical era, when the radiative
forcing was relatively small compared to the present. The Hadley
Centre started their experiments performed with HadCM2 with
forcing from the middle industrial era, about 1860 Mitchell et
al., 1995 and Johns et al., 1995. The greenhouse gas only
integrations, HadCM2GG, used the combined forcing of all the
greenhouse gases as an equivalent CO2 concentration. A further
series of integrations, HadCM2GS, used the combined equivalent
CO2 concentration plus the negative forcing from sulphate
aerosols. The HadCM2GG integrations simulated the change in
forcing of the climate system by greenhouse gases since the
early industrial period (taken by HadCM2 to be 1860). The
addition of the negative forcing effects of sulphate aerosols
represents the direct radiative forcing due to anthropogenic
sulphate aerosols by means of an increase in clear-sky surface
albedo proportional to the local sulphate loading (refer to
Mitchell et al., 1995 for details of this method). The indirect
effects of aerosols were not simulated. The modelled control
climate shows a negligible long term trend in surface air
temperature over the first 400 years. The trend is about +0.04
degrees C per century, which is comparable to other such
experiments. HadCM2CON represents an improvement over previous
generations of GCMs that have been used at the Hadley Centre
(Johns et al., 1995 and Airey et al., 1995). The experiments
performed have simulated the observed climate system using
estimated forcing perturbations since 1860. Johns et al., (1995)
and Mitchell et al., (1995) have established that HadCM2's
sensitivity is consistent with the real climate system. The
agreement between the observed global-mean temperature record
and that produced in these experiments is better for HadCM2GS
than for HadCM2GG. This implies that HadCM2Gs has captured the
observed signal of global-mean temperature changes better than
HadCM2GG for the recent 100-year record. The climate
sensitivity of HadCM2 is about 2.5 degrees C 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. Data are available for the following
periods: 1961-1990, 2010-2039; 2040-2069; and 2090-2099 Mean
monthly and change fields.

哈德利中心（Hadley Centre）近期开展的实验采用了新型统一模式（Unified Model，Cullen, 1993）。此类实验在全球气候模式（General Circulation Models, GCMs）模拟气候变化的范式上迈出了重要一步，为情景构建带来了全新可能。本实验解决了前几代平衡态（约对应政府间气候变化专门委员会1990年报告，IPCC 1990）与冷启动瞬态（约对应IPCC 1992年报告）气候变化实验中存在的多项核心难题。

HadCM2的空间分辨率为2.5°×3.75°（纬度×经度），对应的网格单元分辨率为96×73个网格盒。其地表空间分辨率约为417km×278km，在南北纬45°处缩减为295km×278km，等效于T42谱分辨率。HadCM2的平衡气候敏感度（DT2x）——即有效CO₂浓度翻倍后的全球平均温度响应——约为2.5℃，不过该数值会随所考虑的时间尺度发生变化。这一数值略低于多数其他全球气候模式（IPCC, 1992）。

若要开展“暖启动”实验，需以早期历史时期的辐射强迫作为模型扰动项，彼时的辐射强迫相较于当前水平相对较低。哈德利中心使用HadCM2开展的实验以1860年左右的工业革命中期作为强迫起始点（Mitchell et al., 1995; Johns et al., 1995）。其中仅考虑温室气体的积分实验（HadCM2GG）以等效CO₂浓度下所有温室气体的综合强迫作为驱动条件；另一组系列积分实验（HadCM2GS）则在等效CO₂浓度综合强迫的基础上，叠加了硫酸盐气溶胶的负强迫。HadCM2GG模拟了自1860年（本实验设定的工业革命早期起点）以来，温室气体对气候系统强迫的变化。硫酸盐气溶胶负强迫的加入，代表了人为源硫酸盐气溶胶通过晴空地表反照率随局地硫酸盐载荷比例升高而产生的直接辐射强迫（相关方法细节参见Mitchell et al., 1995），气溶胶的间接效应未被纳入模拟。

模拟的对照气候在前400年的地表气温长期趋势可忽略不计，其趋势约为每百年+0.04℃，与其他同类实验的结果相当。HadCM2CON相较于哈德利中心此前使用的前几代全球气候模式（Johns et al., 1995; Airey et al., 1995）实现了改进。

本次实验利用1860年以来估算的强迫扰动，对观测到的气候系统进行了模拟。Johns等人（1995）与Mitchell等人（1995）已证实，HadCM2的气候敏感度与真实气候系统相符。相较于HadCM2GG，HadCM2GS的模拟结果与观测到的全球平均温度记录的吻合度更高，这意味着在近百年的温度记录中，HadCM2GS对全球平均温度变化的观测信号捕捉效果优于HadCM2GG。HadCM2的气候敏感度约为2.5℃。

A2排放情景的核心导向为强化区域与本土文化，多数区域回归家庭价值观念。A2情景下的世界将整合为若干大致以大陆为界的经济区域，强调本土文化根源。部分区域中，宗教参与度的提升促使许多人摒弃物质主义路径，转而专注于为本地社区做贡献；而其他区域则呈现出加大教育与科研投入、经济生产率提升的趋势。社会与政治结构呈现多元化特征：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“精简型”政府。环境问题相对不受重视，仅部分区域关注控制本地污染与维护本地环境宜居性。

相较于A1与B1情景，A2情景下的国际紧张局势更多，国际合作更少。人员、思想与资本的流动性降低，技术扩散速度缓慢。区域间生产率乃至人均收入的差距持续存在甚至扩大。由于情景侧重家庭与社区生活，生育率仅缓慢下降（不同区域存在差异），因此该情景族的人口增长较快，到2100年将达到150亿；相较于A1与B1情景，其人均收入水平较低，2050年约为7200美元，2100年约为16000美元。

部分区域的技术变革速度较快，部分区域则较慢，这是因为工业部门需要适配本地的资源禀赋、文化与教育水平。能源与矿产资源丰富的区域将发展资源密集型经济，而资源匮乏的区域则将通过技术创新提升资源利用效率、开发替代投入品，将降低进口依赖度作为核心优先级。不同区域的燃料结构主要由资源可得性决定。区域间的技术结构分化持续存在：高收入但资源匮乏的区域将转向先进的后化石能源技术（土地充裕区域发展可再生能源，人口稠密且资源匮乏区域发展核电），而低收入且资源丰富的区域则普遍依赖老旧的化石能源技术。

由于存在大量粮食需求，农业生产率成为该未来情景下创新与研发（Research and Development, R&D）工作的核心聚焦领域之一。初期严重的土壤侵蚀与水污染问题，最终将通过本地发展可持续高产农业得到缓解。尽管关注潜在的本地与区域环境破坏，但该问题在不同区域的重视程度并不均衡。例如，亚洲地区由于健康与农业生产受影响，会减少硫与颗粒物排放；而非洲地区则因加大煤炭与其他矿产资源开发力度，此类排放有所增加。

A2情景下的能源与碳强度较高，相应的温室气体（Greenhouse Gas, GHG）排放量也较高，其CO₂排放量在四类情景族中位居首位。

本数据集涵盖以下时段：1961-1990年、2010-2039年、2040-2069年及2090-2099年，包含月平均场与变化场数据。