exact changes to 1995 IPCC report*:
the crucial chapter 8 for the "Summary for Policymakers"
*Material taken from SEPP: IPCC controversy here
Also see Singer's Letter
to IPCC Scientists which states his belief that
Chapter 8 was altered substantially in order to make it conform
to the Summary. "Three key clauses - expressing the
consensus of authors, contributors, and reviewers - should
have been placed into the Summary instead of being deleted
from the approved draft chapter; and the ambiguous phrase
"the balance of evidence suggests a discernible human
influence on global climate" has been (mis)interpreted
by policymakers to mean that a major global warming catastrophe
will soon be upon us."
Singer says: I have now learned that convening lead author
Ben Santer was instructed (prevailed upon?) by IPCC WG-I co-chairman
John Houghton to make changes to Chapter 8 following the Madrid
meeting. Santer should therefore not be accused of
having committed these actions independently, even
though he himself has always claimed personal responsibility
for the alterations. In reviewing all of my written statements,
whether public or private, I do not find any "attack"
on Santer; I will say, however, that he has not been forthcoming
with the necessary information.
NOTE: The original Working Group I report was approved
by the IPCC in December, 1995. Subsequent to that approval,
IPCC has apparently allowed additional edits to the document.
Some changes are editorial, serving to add clarification or
to correct sentence structure. However, other changes appear
to go beyond that and have the effect of changing the substance
and tone of this chapter. The most significant edits are identified
below. New material is italicized, deleted material
strike through it.
from the Intergovernmental Panel on
Climate Change, Second Assessment
Report, Working Group I, Chapter Eight
Many but not all The Majority
of these studies show that the observed changes in global-mean,
annually-averaged temperature over the last century
is unlikely to be due entirely to natural fluctuations
of the climate system."
deleted:"The evidence rests heavily
on the reliability of the (still uncertain) estimates
of natural variability noise levels."
new: "Furthermore, the probability
is very low that these correspondences could occur by
chance as a result of natural internal variability.
The vertical patterns of change are also inconsistent
with the response patterns expected for solar and volcanic
"Viewed as a whole, these results indicate that the
observed trend in
global warming mean
temperature over the past 100 years is larger than
our current best estimates of natural climate variations over
the last 600 years. unlikely to be entirely natural
"The attribution of a detected climate change to a particular
can be established only by testing
involves tests of competing hypotheses."
"The claimed statistical detection of an anthropogenic
signal in the observations must always be accompanied by the
caveat that other explanations for the detected climate-change
signal cannot be ruled out completely, unless a rigorous attempt
has been made to do so."
new: "There is, however, an important
distinction between achieving 'practically meaningful' and
'statistically unambiguous' attribution. This distinction
rests on the fact that scientists and policymakers have different
perceptions of risk. While a scientist might require decades
in order to reduce the risk of making an erroneous decision
on climate change attribution to an acceptably low level (say
1-5%), a policymaker must often make decisions without the
benefit of waiting decades for near-statistical certainty."
"We now have: * more relevant model simulations,
for the definition of an anthropogenic climate change signal
and for the estimation of natural internal variability.
* more relevant simulations for the estimation of natural
internal variability, and initial estimates from paleoclimatic
data of total natural variability on global or hemispheric
scales; * more powerful statistical methods for detection
of anthropogenic change, and a better understanding of
simpler statistical methods and increased application
of pattern-based studies with greater relevance for attribution."
Section 8.2.2 Inadequate Representation
new: "Deficiencies in the treatment
and incorporation of feedbacks are a source of signal uncertainty."
"Current pattern-based detection work
has not attempted
is now beginning to account for these forcing uncertainties."
"Initial attempts are now being made
these reasons and many others, scientists have been unable
to use paleoclimate data in order to reconstruct a satisfactory,
spatially-comprehensive picture of climate variability over
even the last 1,000 years. Nevertheless, The process
of quality-controlling paleoclimatic data, integrating information
from different proxies, and improving spatial coverage should
be encouraged. Without a Better paleoclimatic data
bases for at least the past millennium, it will be difficult
are essential to rule out natural variability as
an explanation for recent observed changes, or to and
validate coupled model noise estimates on century time scales
(Barnett et al., 1995)."
deleted: "While such studies help to
build confidence in the reliability of the model variability
on interannual to decadal time scales, there are still serious
concerns about the longer time scale variability, which is
more difficult to validate (Barnett et al., 1995). Unless
paleoclimatic data can help us to 'constrain' the century
time scale natural variability estimates obtained from CGCMs,
it will be difficult to make a convincing case for the detection
and attribution of an anthropogenic climate change signal."
deleted : "While none of these studies
has specifically considered the attribution issue, they often
draw some attribution-related conclusions, for which there
is little justification."
"The conclusion that can be drawn from this body of
work, and earlier studies reported in Wigley and Barnett (1990)
is that the warming trend to date is unlikely to have occurred
by chance due to internally-generated variability of the climate
, although this explanation cannot be ruled out.
This, however, does not preclude the possibility that a significant
part of the trend is due to natural forcing factors. Implicit
in such studies is a weak attribution statement--i.e., some
(unknown) fraction of the observed trend is being attributed
to human influences. Any such attribution-related conclusions,
however, rest heavily on the reliability of our estimates
of both century time-scale natural variability and the magnitude
of the observed global warming mean trend. At best, therefore,
Trend significance can only provide provides
circumstantial support for the existence of an anthropogenic
component to climate change , but does not directly address
the attribution issue."
"These empirical estimates of
such studies offer support of a DT2x are subject
to considerable uncertainty, as shown in a number of studies
(see, e.g., Wigley and Barnett, 1990; Wigley and Raper, 1991b;
Kheshgi and White; 1993b). In summary, such studies offer
support for a DT2x value similar to that obtained by GCMs,
and suggest that human activities have had a measurable
impact on global climate, but they cannot help
to establish a unique link between anthropogenic forcing
changes and climate change."
new: "Implicit in these global
mean results is a weak attribution statement--if the observed
global mean changes over the last 20 to 50 years cannot be
fully explained by natural climate variability, some (unknown)
fraction of the changes must be due to human influences".
deleted: "None of the studies cited
above has shown clear evidence that we can attribute the observed
changes to the specific cause of increases in greenhouse gases."
new: "To date, pattern-based studies have not been
able to quantify the magnitude of a greenhouse gas or aerosol
effect on climate. Our current inability to estimate reliably
the fraction of the observed temperature changes that are
due to human effects does not mean that this fraction is negligible.
The very fact that pattern-based studies have been able to
discern sub-global-scale features of a combined CO2 + aerosol
signal relative to the ambient noise of natural internal variability
implies that there may be a non-negligible human effect on
new: "Simultaneous model-observed
agreement in terms of changes in both global means and patterns,
as in the recent study by Mitchell et al. (1995a), is even
less likely to be a chance occurrence or the result of compensating
"Finally we come to the
most difficult question
of all: 'When will the detection and unambiguous attribution
of human-induced climate change occur ?' when the
detection and attribution of human-induced climate change
is likely to occur. The answer to this question must be subjective,
particularly In the light of the very large signal and
noise uncertainties discussed in this Chapter , it is not
surprising that the best answer to this question is 'We do
not know'. Some scientists maintain that these uncertainties
currently preclude any answer to the question posed above.
Other scientists would and have claimed, on the basis
of the statistical results presented in Section 8.4,
that confident detection of a significant climate
change has already occurred. As noted in Section 8.1,
attribution involves statistical testing of alternative explanations
for a detected observed change and Few if any
would be willing to argue that completely unambiguous
attribution of (all or part of) this change to
anthropogenic effects has already occurred, or was likely
to happen in the next several years."
new: "However, evidence from the
patterned-based studies reported on here suggests that an
initial step has now been taken in the direction of attribution,
since correspondences between observations and model predictions
in response to combined changes in greenhouse gases and anthropogenic
* have now been seen both at the surface and in the
vertical structure of the atmosphere;
* have been found in terms of complex spatial patterns
rather than changes in the global mean alone;
* show an overall increase over the last 20 to 50 years;
* are significantly different from out best model-based
estimates of the correspondence expected due to natural internal
Furthermore, although quantitative attribution studies
have not explicitly considered solar and volcanic effects,
our best information indicates that the observed patterns
of vertical temperature change are not consistent with the
responses expected for these forcings.
The body of statistical evidence in Chapter 8, when examined
in the context of our physical understanding of the climate
system, now points toward a discernible human influence on
global climate. Our ability to quantify the magnitude of this
effect is currently limited by uncertainties in key factors,
including the magnitude and pattern of longer-term natural
variability and the time-evolving patterns of forcing by (and
response to) greenhouse gases and aerosols."
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