Environmental Engineering Reference
In-Depth Information
In spite of these considerations, the following facts can be evidenced, according
to data reported in [ 50 ]:
(1) warming of the climate system is unequivocal, as shown by increases of
average air and ocean temperatures, rising of average sea level and widespread
of ice. In the period 1995-2006, 11 years out of 12 have resulted the warmest
years since 1850. The linear warming trend over the 50 years in the period
1956-2005 (0.13C/decade) is nearly twice that of the period 1906-2005
(100 years). This increase is extremely significant, especially if compared with
the temperature rise which caused the end of the Glacial Period (about 1.5C
in more than 5000 years). Furthermore, since 1961, the temperature of average
global ocean has increased at depths of at least 3000 m, while average sea
level has risen of 1.8 mm/year in the period 1961-2003, and of 3.1 mm/year in
the period 1993-2003. Satellite data since 1978 show that annual average
Arctic sea ice has shrunk by 2.7%/decade.
(2) many natural systems of both continents and oceans are being affected by
regional temperature increases. Observations since 1980 evidence earlier
''greening'' of vegetation in the spring and several changes in marine and
freshwater biological systems.
(3) annual emissions of the most important anthropogenic greenhouse gas (CO 2 )
have grown by about 80% in the period 1970-2004, from 21 to 38 gigatons,
and represent 77% of the total anthropogenic greenhouse gases emissions in
2004, mostly due to energy supply, transport and industry (see Table 1.2 for
percentage data of CO 2 emissions). The global atmospheric concentration of
CO 2 has increased from a pre-industrial value of about 280 ppm to 379 ppm in
2005. The annual CO 2 concentration growth rate was larger during the period
1995-2005 (average of 1.9 ppm/year) with respect to the whole period of
observation available (1960-2005, with an average of 1.4 ppm/year).
(4) global atmospheric concentration of other most important greenhouse gases
(CH 4 and N 2 O) has increased as a result of human activities since 1750 and is
now much higher than pre-industrial values. Methane has increased from a
pre-industrial value of about 715-1732 ppb in the early 1990, and was
1774 ppb in 2005. Nitrogen oxide concentration increased from a pre-indus-
trial value of about 270-319 ppb in 2005. Many halocarbons, which were
practically absent in the atmosphere in pre-industrial era, has increased up to
values in the order of hundreds of ppt.
(5) anthropogenic contributions to aerosol emissions (sulfate, particulate carbon,
nitrate and dust) can produce an appreciable but not determinant cooling effect.
(6) feedback agents can amplify the response to a given climate forcing agent. The
role of water vapor as a positive feedback agent has already been examined
before, but another positive feedback can be produced by CO 2 , in fact
warming reduces both terrestrial and ocean CO 2 uptake, leaving higher con-
centration of this gas in the atmosphere for a given emission scenario.
The conclusions drawn by the experts of IPCC, based on the facts above
reported and on statistical analysis, is that the observed increase in global average
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