IPCC Climate Change Data: CSIRO A2a Model: 2020 Radiation

The CSIRO Atmospheric Research Mark 2b climate model (Hirst
et al., 1996, 1999) has recently been used for a number of more
sophisticated climate change simulations. These start from 1880
to avoid the "cold start problem". This version of
the CSIRO model includes the Gent-McWilliams mixing scheme in
the ocean and shows greatly reduced climate drift relative to
earlier versions (e.g. Dix and Hunt, 1998). The drift in global
mean surface temperature in the new control run is about -0.02
degrees C/century. Note that the model uses flux correction.
The model atmosphere has 9 levels in the vertical and horizontal
resolution of spectral R21 (approximately 5.6 by 3.2 degrees).
The ocean model has the same horizontal resolution with 21
levels. The equilibrium sensitivity to doubled CO2 of a mixed
layer ocean version of the model is 4.3 degrees. This is at the
high end of the range of model sensitivities (e.g. IPCC 1995,
Table 6.3). In the basic greenhouse gas experiment the model
combines the effect of all radiatively active trace gases into
an "equivalent" CO2 concentration. Observed
concentrations are used from 1880 to 1990 and the IS92a
projections into the future. This gives close to a 1%/year
compounding increase of equivalent CO2. Another model
experiment includes the negative radiative forcing from
atmospheric sulphate aerosol. The direct aerosol forcing is
included via a perturbation of the surface albedo, similarly to
the Hadley Centre experiments described by Mitchell et al (1995)
and Mitchell and Johns (1997) . The sulphate concentrations are
the same as used in the Hadley Centre experiments. However the
chosen aerosol optical properties are different, giving a
present day forcing due to anthropogenic sulphate of about -0.4
W/m^2. This can be compared to the 1880-1990 greenhouse gas
forcing of about 2 W/m^2. The magnitude of the 20th century
warming in the model including aerosol matches the observed
reasonably well. However there are a number of forcings missing
from the model, including solar variability, sulphate indirect
effect and the effect of soot. The climate sensitivity of
CSIRO-Mk2 is about 4.3 degrees C (Watterson et al.,1997). 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.