IPPC did exactly what should be avoided in objective science!

Have you ever read the work by Intergovernmental Panel on Climate Change and felt disturbed by terms like “Medium agreement” or “Robust evidence”? Such terms origin in a document called: Guidance Note for Lead Authors of the IPCC Fifth Assessment Report on Consistent Treatment of Uncertainties “These guidance notes are intended to assist Lead Authors of the Fifth Assessment Report (AR5) in the consistent treatment of uncertainties across all three Working Groups.” In short it describes: “The following summary terms are used to describe the available evidence: limited, medium, or robust; and for the degree of agreement: low, medium, or high. ”

Please have a look at the Guidance Note linked above. It is well worth a read.

And if you get a feeling that the Guidance Note is not at all very scientific, you will probably find the following quotes by Karl Popper to be of interest:
Karl Popper; The logic of scientific discovery;
8 SCIENTIFIC OBJECTIVITY AND SUBJECTIVE CONVICTION
(Karl Popper was the master mind behind critical rationalism)

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“We may now return to a point made in the previous section: to my thesis that a subjective experience, or a feeling of conviction, can never justify a scientific statement, and that within science it can play no part… No matter how intense a feeling of conviction it may be, it can never justify a statement. Thus I may be utterly convinced of the truth of a statement; certain of the evidence of my perceptions; overwhelmed by the intensity of my experience: every doubt may seem to me absurd. But does this afford the slightest reason for science to accept my statement? Can any statement be justified by the fact that Karl R. Popper is utterly convinced of its truth? The answer is, ‘No’; and any other answer would be incompatible with the idea of scientific objectivity.”

 ….

“from the epistemological point of view, it is quite irrelevant whether my feeling of conviction was strong or weak; whether it came from a strong or even irresistible impression of indubitable certainty (or ‘self- evidence’), or merely from a doubtful surmise. None of this has any bearing on the question of how scientific statements can be justified. Considerations like these do not of course provide an answer to the problem of the empirical basis. But at least they help us to see its main difficulty. In demanding objectivity for basic statements as well as for other scientific statements, we deprive ourselves of any logical means by which we might have hoped to reduce the truth of scientific statements to our experiences. Moreover we debar ourselves from granting any favoured status to statements which describe experiences, such as those statements which describe our perceptions (and which are sometimes called ‘protocol sentences’).

Whatever may be our eventual answer to the question of the empirical basis, one thing must be clear: if we adhere to our demand that scientific statements must be objective, then those statements which belong to the empirical basis of science must also be objective, i.e. inter-subjectively testable. Yet inter-subjective testability always implies that, from the statements which are to be tested, other testable statements can be deduced. Thus if the basic statements in their turn are to be inter-subjectively testable, there can be no ultimate statements in science: there can be no statements in science which cannot be tested, and therefore none which cannot in principle be refuted, by falsifying some of the conclusions which can be deduced from them.”

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The intergovernmental Panel on Climate Change regard itself as a scientific body. About IPCC.

However – in summary:
Judging by the works of Karl Popper:

The “Guidance Note on Consistent Treatment of Uncertainties by IPCC”  is largely incompatible with the idea of scientific objectivity.

Revision history:
2015-11-22 Format changes + links + sentence on critical rationalism