Geoscience Reference
In-Depth Information
— sea levels will probably rise by 18 to 59 cm (7.08 to 23.22 in).
— there is a confidence level >90% that there will be more frequent warm
spells, heat waves and heavy rainfall.
— there is a confidence level >66% that there will be an increase in droughts,
tropical cyclones and extreme high tides.
Both past and future anthropogenic carbon dioxide emissions will continue
to contribute to warming and sea-level rise for more than a millennium.
●
Global atmospheric concentrations of carbon dioxide, methane, and nitrous
oxide have increased markedly as a result of human activities since 1750 and
now far exceed pre-industrial values over the past 650,000 years.
●
In IPCC statements 'most' means greater than 50%, 'likely' means at least a 66%
likelihood, and 'very likely' means at least a 90% likelihood.
Important points in this chapter
What are General Circulation Models (GCMs)?
Computer programs which
describe atmosphere circulation using equations that portray conservation
and movement of atmospheric constituents, incoming solar radiation and
outgoing longwave radiation, and transfers between the atmosphere and
oceans and continents. Currently GCMs describe changes in the atmosphere
every 20-30 minutes at points separated by 10s-100s of kilometers in the
horizontal and by 10s-1000s of meters in the vertical.
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How are GCMs used?
To give:
—
numerical weather prediction (NWP)
in which an observation-based
description of the current atmosphere is extrapolated forward for several
(typically 3-8) days to calculate the
actual weather
likely to occur over
this period.
—
globally-available atmospheric 'data'
provided by GCMs as a byproduct of
the process necessary to define the initial state of the atmosphere prior to
an NWP run, with four-dimensional data assimilation used to define a
weighted average description between that previously predicted by the
GCM and all relevant observations available at the time of initiation.
—
climate prediction
in which it is assumed that, although they are not able
to predict
actual weather
for more than a few days, GCMs are able to
predict the
statistics of weather
, i.e., climate, for periods up to many cen-
turies ahead.
●
How do GCMs Work?
Once an initial state of the atmosphere has been
defined, equations coded in the GCM are applied at each time step in two
groups sequentially;
—
the dynamics,
equations that control the model's state variables solved
assuming fixed values for variables (such as flux divergences) that deter-
mine changes in state variables; and
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