Geoscience Reference
In-Depth Information
middle latitudes, is of special interest here, as is a similar lack of agreement about
the changing frequency of occurrence of tropical cyclones under global warming.
An important future task is to improve climate models, aimed at reaching eventually
a level of reliability that would enable the prediction of climatic changes.
Allen (2002) has discussed the basic conclusions contained in the
“
Summary for
policy-makers
”
(SPM) of the Third IPCC Report and especially of its main con-
clusion that
There is new and stronger evidence that most of the warming observed
during the last 50 years should be attributed to human activity
“
”
. This conclusion
supplements the statement according to which
as follows from the present climate
models, it is very unlikely that the warming taking place during the last 100 years
was determined only by the internal variability
“
means that there is
less than one chance of ten for an opposite statement to be well-founded).
Clearly, the reality of such a statement depends on an adequate modeling of the
observed climatic variability. Analysis of the results of the relevant calculations using
six different models has shown that three of six models reproduce climate variability
on time scales from 10 to 50 years which agrees with the observational data.
Another conclusion in SPM (TAR) is that
”
(
“
very unlikely
”
reconstruction of data on climate for
the last 1,000 years shows that the present warming is unusual and it is unlikely that
it can be only of natural origin
“
”
(
“
unlikely
”
means that there is less than one chance
of three for an opposite conclusion).
This conclusion is supplemented with the following:
Numerical modeling of the
response to only natural disturbing forces does not explain the warming that took
place in the second half of the 20th century
”
. This view is based on the analysis of
the results from the numerical modeling of changes in the average global SAT during
the last 50 years. It follows from this that a consideration of natural forcings (solar
activity, volcanic eruptions) has demonstrated a climatic cooling (mainly due to
large-scale eruptions in 1982 and 1991) which has allowed the conclusion that the
impact of only natural climatic factors is unlikely. However, there is only one chance
in three that it was so: such carefulness is due to insuf
“
cient reliability based on
indirect information concerning natural forcings in the past.
Results of numerical modeling cannot explain the pre-1940 climate warming
with only anthropogenic factors taken into account, but are quite adequate con-
sidering both natural and anthropogenic impacts (GHGs and sulphate aerosol). As it
was mentioned in SPM of TAR,
“
these results
…
do not exclude possibilities of
contributions of other forcings
. It is possible therefore that good agreement of the
calculated and observed secular trends of SAT may in part be determined by a
random mutual compensation of uncertainties. Another important illustration of the
inadequacy of the numerical modeling results is their difference with observations
concerning temperature changes near the Earth
”
s surface and in the free tropo-
sphere. If, as according to models, the tropospheric temperature increases more
rapidly than near the surface, then the analysis of observational data between 1979
and 2000 reveals that the temperature increase in the free troposphere is slower and
probably is absent at all (Chou et al. 2002; Collins et al. 1998; Conant et al. 2002).
When assessing the content of the IPCC-2001 Report, Griggs and Noguer (2002)
argued that this report:
'
Search WWH ::
Custom Search