jim - // It's possible to evaluate how much someone does or does not understand science, or a particular aspect of it, based on what they say. //
Not really - there is neither the time or the inclination to offer everything I know about science, and for the purposes of this debate, climate change is a secondary issue - we are debating Ms Thunberg and her re-emergence, not climate change itself.
// In this case, parroting the line that "the planet is warming up because it always has" betrays a basic misunderstanding: firstly, because it's simply wrong: the planet's temperature is indeed variable but can warm up as well as cool down. //
That statement does not make sense. On the one hand you agree with my point that the planet is warming up, and on the other hand you point out that the temperature is variable and can warm up as well as cool down - which does not contradict my point, or make it 'wrong'.
I am unsure how old you are, but I am old enough to remember scientists in the 1970's advising us that a 'New Ice Age' was on the way - that didn't happen, science is fallible.
// Secondly, because the natural variation of the planet's climate has not escaped the attention of climate scientists -- indeed, it is to those same scientists that we owe this discovery; and thirdly because it ignores the very clear signal in recent decades on top of that background, which can be attributed overwhelmingly to human activity. //
Well, firstly to call yourself a 'climate scientist' is simply to decide to follow an aspect of science, it does not make you right in your analysis and predictions, either in terms of cause and effect, or the long-term prospects of the planet.
Some have jumped on a fashionable bandwagon and made some fame and money out of it. Some, like scientists have a claim to know of what they speak, which is fine, but does not make them right by any means.
Some, like Ms Thunberg, the subject of the thread lest we forget - has been put forward as some sort of visionary by doing nothing more than spouting information she is fed in a way that is designed to make people of her age think that she has something new and important to say.