chapter - Atmospheric and Oceanic Science

12.6.1. Baseline scenarios
It is convenient to define a baseline scenario or observed climate with regard
to which the changes in the different climate scenarios can be referred. The election
of this baseline or reference period is frequently determined by the availability of
climatic information. Most of the impact assessment studies aim to determine the
effects of the change with respect to current conditions, and so they used recent
base periods such as 1961-90. It is important to have in mind that no matter whatever
the baseline period is, there are differences between climatic averages based
on long periods of time (for instance, 100 years) and those considering shorter subperiods.
Moreover, different 30-years periods show differences in regional annual
mean temperatures of ±0.5°C and of ±15% in annual precipitation (Hulme and New
1997; Visser et. al. 2000). Thus small regional changes in future climate scenarios
cannot be consider significant.
12.6.2. Global scenarios
Climate scenarios
Scenario A2 proposed by the IPCC implies that in less than a century, carbon
dioxide concentrations will reach more than three times pre-industrial levels,
methane concentration will be more than 5 times and those of nitrous oxide will
almost double. It is important to highlight that these values have never been reached
at least in the last 20 millions years.
For year 2060, GCM project an increase of the global surface temperature of
1.3 to 2.5°C depending on the socio-economic scenario, with higher warming at
high latitudes and in winter. This warming would not be uniform; in the continental
areas of the northern hemisphere there would be regions where temperature
would raise more than 8ºC. Table 12.2 shows mean projections of temperature rise
for different decades up to 2100 with respect to the period 1961-90 for different scenarios.
Beyond that date the increase of the temperatures could be much higher,
critically depending on the future evolution of the GHG emissions.
Table 12.2. Increase in the surface mean global temperature (ºC) for different
socio-economic scenarios.
SCENARIOS
A1 A2 B1 B2
2000 0,15 0,15 0,15 0,15
2020 0,50 0,50 0,50 0,60
2040 1,20 1,00 0,90 1,10
2060 2,50 1,80 1,30 1,60
2100 4,50 3,80 2,00 2,70
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