I learned from medicine that it is much harder, sometimes in practice impossible, to test therapeutic claims for drugs and treatments which are supposed to affect long-term and unpredictable processes.
For example, it was easy to show that lithium had a calming effect in mania, but very difficult to show that when lithium is taken long-term ('prophylactically') it can (probably, potentially, and with severe disadvantages and side effects) reduce the frequency of manic episodes.
But the 'mood stabilizing drugs' which have been marketed so successfully to replace lithium were adopted within a timescale of years, not decades, and therefore before there had been any possibility of testing their effectiveness in the treatment of such a long-term and variable condition as mania.
Therefore we know for sure these drugs were in fact (not as a matter of opinion) adopted without evidence, on the basis of hype.
Another medical example was the supposed effects of diet changes on the incidence of coronary heart disease.
These dietary changes (low cholesterol, high polyunsaturates, low fat overall etc) were recommended and implemented at a population level long before there had been any possibility of testing whether they a.) worked or b.) were overall beneficial - since this would have taken decades to establish.
Therefore we know for sure that these dietary changes (and others such as the eating of 'five a day' fruits and vegetables) were in fact adopted without evidence and on the basis of hype.
The necessary and sufficient ground for rejecting the claims of the advocates of 'man-made climate change' is that there is no way they could possibly know whether their claims are true.
(Or to put it the other way about: it is im-possible - i.e. not-possible, i.e. literally beyond possibility - for the climate change activists to know what they claim to know.)
In other words, these people are claiming to possess knowledge truly vast in its scope: they claim to be able to understand, predict and influence the climate of the earth. It is not a matter of whether they are right or wrong in their claims - but that their claims are pre-evidential; they have not even reached the level of being able to discuss whether they are right or wrong.
They are just ideas, notions, suggestions - not even formulated sufficiently to count as formal-hypotheses.
Because of the very large temporal (year-by-year) variation in climate/ temperatures, the timescale over which one can be confident of measuring a climate trend is of the order of many years - in fact, a few decades.
In other words, because temperature varies so widely according to time and place, we could not know whether we really understood the causes, really could predict the future, and really could engineer global climate without many decades of measurement and testing of hypotheses.
It follows that the timescale of 'a few decades' would also be the absolute minimum time over which it could be tested whether hypotheses/ models of climate change were valid.
Thus it is necessary to: 1. put forward a specific hypothetical model of climate change, 2. use the model make precise predictions of future climate, and 3. measure future climate over a period of decades to compare the predictions of the model with what is observed.
Only if future observations matched with predictions would it be reasonable to assert that the model of climate change was accurate; and only if the model was accurate in these predictions would it be reasonable to believe that understanding of the causes of global climate had been achieved; and only if changes (against trend) had been mapped against outcomes would it be possible legitimately to claim that by changing the magnitude of these causes there was any genuine possibility of really controlling the earth's climate.
But this necessary process, lasting a few decades, was not followed. There never was a decades-long period between the construction of hypothetical climate models and their testing.
Therefore, we know for sure that the theories of anthropogenic climate change, the focus on carbon dioxide, the vast multi-trillion dollar government programs to change the world economy to prevent global warming - all of these and the rest of it was in fact (and not as a matter of opinion) adopted without evidence, on the basis of hype.
Without this necessary period of testing; claims to be able to understand the causes of climate, predict future climate changes, and influence the future global climate have zero validity.
As the TV astronomer Patrick Moore used to say when he had reached the limits of solid knowledge: We just don't know.
Whether there has been global warming in recent decades (in the past, from here backwards) is a matter of evidence and interpretation.
But, whether there will be (in the future, from now onwards) global warming - and whether future climate change is controllable by human action - is unknown, a matter of sheer assertion, purely conjectural.
And this is not just a matter of opinion. To disagree is proof of either scientific incompetence or personal dishonesty (or both).