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decreased
by
10%
since
the
1960s.
Precipitation has increased by about 0.2-
0.3% per decade in tropical continental
zones and decreased by 0.3% per decade in
continental regions between 10ºN-30ºN in
the
northern
hemisphere.
On
the
other
hand,
the
frequency
of
extreme
precipitation events occurrence increased
from 2 to 4%. The increase in CO2 had
already
reached
31%
since
1750,
the
highest in the last 450,000 years. There is
larger evidence that most of the observed
warming is attributable to human activity,
mainly during the second half of the 20th
century. The report emphasized that:
Without significant reductions in GHG
emissions,
global
warming
would
continue and have severe and potentially
irreversible
impacts
on
natural
and
human systems.
The
IPCC
report
released
worldwide
projections based on certain assumptions
of economic, demographic, technological
development, environmental policies, and
social equity. These projections indicated
that the global average temperature could
increase between 1.4 and 5.8 ºC towards
the end of the 21st century. Changes in
precipitation
regimes
would
occur
with
increases in polar latitudes and decreases in mid-latitudes. In addition, increases
in extreme weather events such as heat waves and heavy rainfall, drought
events, and tropical cyclones were projected through the present century.
The Fourth Report (IPCC, 2007) concluded that the warming of the climate
system is unequivocal, as revealed by the evidence and environmental data
analysis from the atmosphere and the ocean, by the significant shrinkage of the
cryosphere, and the rise in mean sea level, among others. Until 2006 (the last
year included in the Fourth Report), the total temperature increased by 0.76ºC
(0.57 -0.95ºC) from 1850-1899 to 2001-2005. The mean sea level rose about