IPCC Climate Change Data: HADCM3 A2a 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）近期开展的试验采用了新型统一模式（Unified Model，Cullen, 1993）。此类试验在全球气候模式（General Circulation Models, GCM）模拟气候变化的范式上迈出了重要一步，为情景构建带来了新的可能。该试验攻克了前几代平衡态试验（equilibrium，约对应政府间气候变化专门委员会<Intergovernmental Panel on Climate Change, IPCC>1990年报告中的相关试验）与冷启动瞬态试验（cold-start transient，约对应IPCC 1992年报告中的相关试验）气候变化试验所面临的若干核心难题。

HadCM2的空间分辨率为2.5°×3.75°（纬度×经度），对应的网格格点总数为96×73个。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℃，但该数值会随考量的时间尺度发生变化。这一数值略低于多数其他GCM（IPCC, 1992）。

开展暖启动实验（warm-start experiment）需采用早期历史时期的辐射强迫（radiative forcing）对模式进行扰动，彼时的辐射强迫远低于当前水平。哈德利中心利用HadCM2开展的试验以1860年左右的工业革命中期为强迫起点（Mitchell et al., 1995; Johns et al., 1995）。

仅考虑温室气体的积分模拟试验（HadCM2GG）采用所有温室气体的综合强迫，以等效CO₂浓度（equivalent CO₂ concentration）表征。另一组积分模拟试验（HadCM2GS）则在等效CO₂浓度的基础上，叠加了硫酸盐气溶胶（sulphate aerosols）的负强迫。HadCM2GG模拟了自1860年（该研究将其定义为工业早期）以来温室气体对气候系统的强迫变化。硫酸盐气溶胶负强迫的加入，代表了人为硫酸盐气溶胶通过晴空地表反照率随局地硫酸盐负载量增加而提升所产生的直接辐射强迫（具体方法详见Mitchell et al., 1995），未模拟气溶胶的间接效应。

模式的控制气候在前400年的地表气温长期趋势可忽略，仅约+0.04℃/百年，与同类试验结果相当。HadCM2CON相较于哈德利中心此前使用的几代GCM（Johns et al., 1995; Airey et al., 1995）有所改进。

本系列试验利用1860年以来的估算强迫扰动，模拟了观测到的气候系统变化。Johns等（1995）与Mitchell等（1995）已证实，HadCM2的气候敏感度与真实气候系统一致。相较HadCM2GG，HadCM2GS的试验结果与观测全球平均气温记录的吻合度更高，表明在近百年观测记录中，HadCM2GS对全球平均气温变化的信号捕捉更优。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，诸多地区回归家庭价值观。A2世界逐步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。部分地区宗教参与度提升，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。其他地区则倾向于加大教育与科研投入，推动经济生产率增长。社会与政治结构呈现多元化：部分地区建立更完善的福利体系，缩小收入不平等差距，而另一些地区则推行“精简型”政府。环境议题受关注度相对较低，仅部分地区着力管控本地污染、维护本地环境宜居性。相较于A1或B1情景，A2世界的国际紧张局势更多，合作更少。人员、思想与资本流动性较弱，技术扩散速度缓慢。区域间生产率乃至人均收入的国际差距持续存在甚至扩大。由于聚焦家庭与社区生活，生育率仅缓慢下降（区域间存在差异），因此该情景家族的人口增长较快，到2100年将达150亿，人均收入相对A1与B1世界较低：2050年为7200美元，2100年为16000美元。

部分地区技术变革迅速，部分地区则较为缓慢，工业部门根据本地资源禀赋、文化与教育水平调整适配。能源与矿产资源丰富的地区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首要任务，以最大限度减少对进口的依赖。不同地区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地区转向先进的后化石燃料技术（土地充裕地区发展可再生能源，人口稠密、资源匮乏地区发展核电），而低收入且资源丰富的地区通常依赖较为陈旧的化石燃料技术。

由于存在大量粮食需求，农业生产率成为该未来场景下创新与研发（Research and Development, RD）工作的核心领域之一。最初较为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，但这种关注在各地区并不均衡。例如，亚洲地区由于健康与农业生产影响的考量，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，导致此类排放增加。A2世界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排放量在四类情景家族中位居最高。

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