IPCC Climate Change Data: ECHAM4 B2a Model: 2080 Mean Temperature

The ECHAM climate model has been developed from the ECMWF
atmospheric model (therefore the first part of its name: EC) and
a comprehensive parameterisation package developed at Hamburg
therefore the abbreviation HAM) which allows the model to be
used for climate simulations. The model is a spectral transform
model with 19 atmospheric layers and the results used here
derive from experiments performed with spatial resolution T42
(which approximates to about 2.8 degrees longitude/latitude
resolution). The model has also been used at resolutions in the
range T21 to T106. ECHAM4 is the current generation in the line
of ECHAM models (Roeckner, et al., 1992). A summary of
developments regarding model physics in ECHAM4 and a description
of the simulated climate obtained with the uncoupled ECHAM4
model is given in Roeckner et al. (1996). The initial sea
surface temperature and sea-ice data is the COLA/CAC AMIP SST
and sea-ice data set. The mean terrain heights are computed from
high resolution US Navy data set. The fraction of grid area
covered by vegetation based on the Wilson and Henderson-Sellers
(1985) data set. The ocean albedo is a function of solar zenith
angle and the land albedo from the satellite data of Geleyn and
Preuss (1983). A diurnal cycle and gravity wave-drag is
included. The time-step of the model is 24 minutes, except for
radiation which uses two hours. The ocean model is an updated
version of the isopycnal model (OPYC3) developed by Josef
Oberhuber (Oberhuber, 1993) at the Max-Planck-Institute for
Meteorology, Hamburg, Germany. The name OPYC is derived from
Ocean and isoPYCnal co-ordinates. The concept to use isopycnals
as the vertical co-ordinate system for an OGCM is based on the
observation that the interior ocean behaves as a rather
conservative fluid. Even over long distances the origin of water
masses can be traced back by considering the distribution of
active or passive tracers. Treating the ocean as a conservative
fluid fails in areas of significant turbulence activity such as
the surface boundary layer. A surface mixed-layer is therefore
coupled to the interior ocean in order to represent near-surface
vertical mixing and to improve the response time-scales to
atmospheric forcing which is controlled by the mixed-layer
thickness. Since the model is designed for studies on large
scales, a sea ice model with rheology is included and serves the
purpose of de-coupling the ocean from extreme high-latitude
winter conditions and promotes a realistic treatment of the
salinity forcing due to melting or freezing sea ice. The
experiments from which results are used here are the 1000-year
unforced control simulation using the coupled ECHAM4/OPYC3 model
and then two climate change simulations. The greenhouse gas only
forced experiment (referred to as GGa1) used historical
greenhouse gas forcing from 1860 to 1990 followed by a 1 per
cent annum increase in radiative forcing from 1990 to 2099. The
greenhouse gas and sulphate aerosol forced experiment (referred
to as GSa1) used the GGa1 forcing, plus the negative forcing due
to sulphate aerosols. This was represented by means of an
increase in clear-sky surface albedo proportional to the local
sulphate loading. The indirect effects of aerosols were not
simulated. For 1860 to 1990 the historic sulphate aerosol
forcing estimate was used and for 1990 to 2049 the aerosol
forcing estimated for the IS92a emissions scenario. The GSa1
experiment did not extend beyond 2049. Fuller details of the
ECHAM4/OPYC3 coupled model can befound at the DDC Yellow Pages.Several papers describe results using this version of the model
- see Bacher et al. (1998), Oberhuber et al. (1998), Zhang et
al. (1998). The climate sensitivity of ECHAM4 is about 2.6
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. 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.