IPCC Climate Change Data: GFDL99 A2a Model: 2020 Mean Temperature

The experiments with the GFDL model used here were performed
using the coupled ocean-atmosphere model described in Manabe et
al. (1991) and Stouffer et al., (1994) and references therein.
The model has interactive clouds and seasonally varying solar
insolation. The atmospheric component has nine finite difference
(sigma) levels in the vertical. This version of the model was
run at a rhomboidal resolution of 15 waves (R15) yielding an
equivalent resolution of about 4.5 degrees latitude by 7.5
degrees longitude. The model has global geography consistent
with its computational resolution and seasonal (but not diurnal)
variation of insolation. The ocean model is based on that of
Byan and Lewis (1979) with a spacing between gridpoints of 4.5
degrees latitude and 3.7 degrees longitude. It has 12 unevenly
spaced levels in the vertical dimension. To reduce model drift,
the fluxes of heat and water are adjusted by amounts which vary
seasonally and geographically, but do not change from one year
to another. The model also includes a dynamic sea-ice model
(Bryan, 1969) which allows the system additional degrees of
freedom. The 1000-year unforced simulation used here is
described in Manabe and Stouffer (1996). The drift in
global-mean temperature during this unforced simulation is very
small at about -0.023 degrees C per century. The two GFDL-R15
climate change experiments used here use the IS92a scenario of
estimated past and future greenhouse gas (GGa1) and combined
greenhouse gas and sulphate aerosol (GSa1) forcing for the
period 1765-2065 (Haywood et al., 1997). For the GGa1 experiment
only the 100-year segment from 1958-2057 are available through
the IPCC DDC. The radiative effects of all greenhouse gases is
represented in terms of an equivalent CO2 concentration, and the
direct radiative sulphate aerosol forcing is parameterised in
terms of specified spatially dependent surface albedo changes
(following Mitchell et al., 1995). Results from these climate
change experiments are discussed in Haywood et al. (1997). The
model's climate sensitivity is about 3.7 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. 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.

本研究采用的GFDL模型实验，基于Manabe等人（1991）与Stouffer等人（1994）及其参考文献中所述的海气耦合模式开展。该模式包含交互式云参数化方案与随季节变化的太阳辐射强迫。大气分量在垂直方向采用9层有限差分（σ）坐标格式。本版本模式采用15波菱形谱分辨率（R15），等效分辨率约为纬度4.5°、经度7.5°。模式采用与计算分辨率匹配的全球地理格点，且包含太阳辐射的季节（而非日循环）变化。

海洋模式基于Bryan与Lewis（1979）的方案，格点间距为纬度4.5°、经度3.7°，垂直方向设12层非均匀分布的分层。为抑制模式漂移，热通量与淡水通量将按季节与区域差异进行调整，且各年份的调整量保持恒定。模式还集成了Bryan（1969）提出的动态海冰模式，为系统引入额外的自由度。

本研究采用的1000年无强迫试验细节见Manabe与Stouffer（1996）。该无强迫试验中全球平均温度的漂移极小，仅约为每百年-0.023℃。

本研究使用的两项GFDL-R15气候变化试验，采用IS92a情景，该情景针对1765-2065年时段，分别估算了仅温室气体（GGa1）以及温室气体与硫酸盐气溶胶协同（GSa1）的辐射强迫，相关细节见Haywood等人（1997）。仅GGa1试验中1958-2057年的百年时段数据可通过IPCC数据分发中心（IPCC DDC）获取。所有温室气体的辐射效应以等效CO₂浓度形式表征，硫酸盐气溶胶的直接辐射强迫则通过指定的空间分布地表反照率变化进行参数化（参考Mitchell等人，1995）。上述气候变化试验的结果已由Haywood等人（1997）详细论述。该模式的气候敏感度约为3.7℃。

A2情景下，全球将整合为若干大致以大陆为单元的经济区域，凸显本土文化根源。部分区域内，宗教参与度提升促使许多民众摒弃物质主义路径，转而聚焦于为本地社区作贡献；其他区域则呈现出加大教育与科研投入、提升经济生产力的发展趋势。社会与政治结构呈现多元化特征：部分区域逐步建立更完善的福利体系并缩小收入差距，而另一些区域则倾向于小政府治理模式。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人居环境维护。

A2情景下的国际紧张局势多于A1与B1情景，国际合作则相对匮乏。人员、思想与资本的流动性较低，导致技术传播速度缓慢。各国间的生产力差距进而人均收入差距将持续存在甚至进一步扩大。由于强调家庭与社区生活，尽管各区域生育率存在差异，但整体下降速度缓慢。因此，该情景家族的人口增长较快，至2100年全球人口将达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。

技术变革的区域差异显著：部分区域技术进步迅速，部分则较为缓慢，这是由于各地区产业需适配本地的资源禀赋、文化传统与教育水平。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，以此作为降低进口依赖的核心目标。不同区域的能源消费结构主要由本地资源禀赋决定。区域间的技术结构差异将持续存在：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，人口密集、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传统化石能源技术。

由于粮食需求庞大，农业生产力是该未来情景下创新与研发工作的核心方向之一。尽管初期土壤侵蚀与水污染问题较为严重，但通过本地发展可持续高产农业，这些问题最终将得到缓解。尽管部分区域会关注本地及区域层面的潜在环境损害，但这种关注度在全球并不均衡。例如，亚洲地区由于考虑到污染物对人类健康与农业生产的影响，会减少硫氧化物与颗粒物排放；而非洲地区则因加大煤炭与其他矿产资源开发力度，导致此类污染物排放增加。

A2情景下的能源与碳强度较高，相应的温室气体（GHG）排放量也较大，其CO₂排放量在四类情景家族中位居首位。本数据集包含以下时段的数据：1961-1990年、2010-2039年、2040-2069年以及2090-2099年的逐月场与变化量场数据。