Projected Change
This map shows the global distribution of projected changes in
December to February (Northern Hemisphere winter, Southern Hemisphere
summer) precipitation from the reference period 1975 to 1995 to
the middle (2040 to 2060) of the current century. These changes
are the response simulated in the Canadian Centre for Climate Modelling
and Analysis (CCCma) global climate model to projected increases in atmospheric greenhouse
gas concentrations and sulfate aerosol loadings associated with
human activity. Precipitation changes are expressed as percentages
to indicate that a given change in precipitation amount is more
important in a region of low average precipitation than in a region
of high average precipitation.
On average, precipitation increases as the century progresses and
the climate warms. Projected precipitation changes are not evenly
distributed geographically or seasonally. Unlike the case for temperature
where warming predominates, there are marked regions of decreasing
as well as increasing precipitation over both land and ocean. Annual
average precipitation generally increases over northern continents,
with the increase concentrated in winter. Evapotranspiration also
increases in the warmer climate. The increase of evapotranspiration,
especially in summer, together with a less robust increase in summer
precipitation, or even a decrease in some areas, leads to projections
of reduced soil moisture over some continental regions. Other features
of the simulated hydrological cycle include more high latitude precipitation
in the form of rain rather than snow.
Explanations
The hydrological cycle speeds up at least partially because the
warmer surface temperatures cause increased evaporation into the
atmosphere which then becomes available for precipitation. The marked
regions of both increasing and decreasing precipitation are associated
with shifts in the broad patterns of atmospheric circulation under
climate warming. The pattern of precipitation change over the Pacific
and adjacent land areas is reminiscent of El Niño and arises
in conjunction with a El Niño -like warming pattern in the
tropical Pacific simulated in the CCCma and some other models.
Data Source
The results are based on climate change simulations made with the
Coupled Global Climate Model (CGCM1)
developed at the Canadian Centre for Climate Modelling and Analysis
of Environment Canada. The projected changes in greenhouse
gases concentrations and aerosol loadings are based on the IS92a
scenario developed in conjunction with the Intergovernmental Panel
on Climate Change to portray one of several possible futures.
The output of the model is produced on a grid of 3.75 degrees
in latitude and longitude. This represents a grid square of approximately
400 kilometres by 300 kilometres at Canadian latitudes.
The digital data for this map can be downloaded
here.
Caution in Interpreting the Map
The aim of global climate models is to simulate past, current,
and future large-scale climate based on the physical principles
governing the climate system. The Canadian Centre for Climate Modelling
and Analysis model is reasonably successful in reproducing
the current climate and the climate change observed over the past
century. Nevertheless, future climate scenario results must be treated
with caution and this is especially the case when results are viewed
at smaller local scales. Regional
climate models are one approach to "downscaling" the
large-scale results from global climate models to more local scales.
These models are under active development in Canada and elsewhere.
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