Question: how do we know what is a stable long term proxy and what is not?
Answer: we do a correlation analysis on part of the record and simple assume the correlation holds for all time.
setting aside your "for all time" hyperbole, within multi-proxy reconstructions, just what specific time frame/period are you challenging. Again, let me ask for the 3rd time: "
notwithstanding other reconstruction proxies like ice-cores, lake/ocean bottom sediment, corals, etc., aren't there any reliable (confirming) tree-ring proxy reconstructions - not any? Not any multi-proxy reconstructions you accept - even those that don't use tree-rings? None?"
Question: what happens when the correlation diverges for the modern record?
Answer: If the proxy tells us what we want hear we invent excuses for why the correlation breaks down for the modern period.
riddle me this Mr. Wizard: is your described 'modern period breakdown' applicable to all proxies... or even to all tree-ring locales... or even to the entirety of your described 'modern period breakdown'? Just answer the question - sure you can! Of course, those temperature reading 'thermometer' thingees are a real inconvenient truth for you, yes?
in any case, for certain trees in certain locales over a certain time period... yes you can whine/wail about the divergence effect. Of course you would prefer to call the work of scientists doing science in attempting to understand the effect, "inventing excuses". Much easier for your denial to ignore such things as global dimming, (likely anthropogenic) air pollution effects, warming induced drought, etc..
Physical science? ROTFL. It is nothing but repeated data mining/p-hacking to find things that tell the academics what they want to hear.
one can only wonder why you so object to having your denial pointed out... why you take such exception to being labeled the denier you are! You should embrace it - be loud and proud about your denial!