IPCC Climate Change Data: HADCM3 A2a Model: 2020 Mean Temperature

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.