IPCC Climate Change Data: ECHAM4 A2a Model: 2080 Radiation

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. 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 andB1 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 and monthly change fields.