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serve the basis for such assessments. The key fact is that it is necessary to distin-
guish between something that can be considered real and which remains uncertain.
As for the future climate forecasts, many uncertainties still remain. This approach
has determined the con
dence in scienti
c community when making concrete
decisions and should be preserved in future
.
Bolin (1999) emphasized that though the IPCC-1995 assessment report contains
the statement that global climate change taking place in the 20th century is partially
determined by humans
”
activity, this conclusion was formulated very carefully. An
evaluation of the probable contribution of random climate variations independent of
humans
'
impact in this context was of principal importance. Results of recent
studies have clari
'
ed this question, showing that random variations of global mean
SAT on time scales from decades to centuries for the last 600 years were within
±
C or less (this conclusion, as has been mentioned above, disagrees with data
of observations from which it follows that SAT changed in the past in wider limits).
In this connection (as Bolin (1999) believes), the skeptics about estimates of the
contribution of anthropogenic warming for the last 50
0.2
°
75 years should be asked
how one can explain a much stronger global warming observed during the last
decades.
In reports of of
-
cial representatives of several countries at Conferences in Kyoto
and Buenos Aires and in mass media, weather and climate anomalies like tropical
hurricanes and unusual El Ni
of were ascribed to the impacts of global warming.
These opinions should, however, be thoroughly tested scienti
ñ
cally, though a
possibility of more frequent anomalous events under conditions of global warming
is not excluded. Therefore, especially urgent becomes the development of methods
of climate forecasts on regional scales, bearing in mind,
first of all, the period of
2008
2012.
In Bolin
-
s (1999) opinion, to assess the socio-economic consequences of the
accomplishment of measures foreseen by the Kyoto Protocol on GHGs emissions
reduction,
'
a combination of
models of climate, carbon cycle, as well as power engineering and socio-economic
development, which will require much more time and much effort. In this respect, a
dif
it
is very important
to develop integral models
—
cult problem is to validate such models in order to analyze their reliability. The
absence of an adequate validation means that the results of numerical modeling
with the use of integral models can be considered only as possible scenarios but not
forecasts.
Characterizing the climatic forcings, Hansen et al. (1998, 1999) pointed out that
they are still not determined with an accuracy that is suf
cient for reliable climate
forecasts. There is reliable information about the GHGs content in the atmosphere,
which determines a positive RF, but serious dif
culties are connected with
assessments of the impacts caused by such factors as atmospheric aerosol, clouds,
land use change, causing a negative RF, which determines a partial compensation of
the
climate warming. One of the consequences of this compensation
consists in a much more signi
“
greenhouse
”
cant role of changes of extra-atmospheric insolation
—
(solar constant
SC) as a climate-forming factor than it was supposed earlier, based
on numerical modeling with only GHGs contribution taken into account (the
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