IPCC Climate Change Data: CSIRO B2a 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). Like B1, the B2 world is one of increased concern for
environmental and social sustainability, but the character of
this world differs substantially. Education and welfare
programs are widely pursued leading to reductions in mortality
and, to a lesser extent, fertility. The population reaches about
10 billion people by 2100, consistent with both the United
Nations and IIASA median projections. Income per capita grows at
an intermediary rate to reach about US$12,000 by 2050. By 2100
the global economy might expand to reach some US$250 trillion.
International income differences decrease, although not as
rapidly as in scenarios of higher global convergence (A1, B1).
Local inequity is reduced considerably through the development
of stronger community support networks. Generally high
educational levels promote both development and environmental
protection. Indeed, environmental protection is one of the few
remaining truly international priorities. However, strategies to
address global environmental challenges are less successful than
in B1, as governments have difficulty designing and implementing
agreements that combine environmental protection with mutual
economic benefits. The B2 storyline presents a particularly
favorable climate for community initiative and social
innovation, especially in view of high educational levels.
Technological frontiers are pushed less than in A1 and B1 and
innovations are also regionally more heterogeneous. Globally,
investment in R and D continues its current declining trend, and
mechanisms for international diffusion of technology and
know-how remain weaker than in scenarios A1 and B1 (but higher
than in scenario A2). Some regions with rapid economic
development and limited natural resources place particular
emphasis on technology development and bilateral co-operation.
Technical change is therefore uneven. The energy intensity of
GDP declines at about one percent per year, in line with the
average historical experience of the last two centuries.
Land-use management becomes better integrated at the local level
in the B2 world. Urban and transport infrastructure is a
particular focus of community innovation, contributing to a low
level of car dependence and less urban sprawl. An emphasis on
food self-reliance contributes to a shift in dietary patterns
towards local products, with reduced meat consumption in
countries with high population densities. Energy systems differ
from region to region, depending on the availability of natural
resources. The need to use energy and other resources more
efficiently spurs the development of less carbon-intensive
technology in some regions. Environment policy cooperation at
the regional level leads to success in the management of some
transboundary environmental problems, such as acidification due
to SO2, especially to sustain regional self-reliance in
agricultural production. Regional cooperation also results in
lower emissions of NOx and VOCs, reducing the incidence of
elevated tropospheric ozone levels. Although globally the energy
system remains predominantly hydrocarbon-based to 2100, there is
a gradual transition away from the current share of fossil
resources in world energy supply, with a corresponding reduction
in carbon intensity.