China is a leading emitter of SO2, with heavy use of low grade, high-sulfur content coal.

Common sources of SO2 have risen in the last decades, from sources such as combustion of dirty pyritic coal and smelting of sulphide mine ores.

By sources rising, do you mean SO2 emissions have increased? I’m not very familiar with coal industries but many sulphide smelting operations are currently undergoing SO2 abatement projects (especially in Canada). Also, with the implementation of more efficient acid plants, I would expect SO2 emissions to have decreased in last decades. I’m not sure we’re on topic here…

One of the plant nutrients between the major N, P, K tio and the traces like Mo and B and Se are the intermediate nutrients. One of these is sulphur, taken up in fair quantity. We have the inverted U probability again. No sulphur and the tree dies. Too much sulphur (commonly derived from atmosphereic SO2) and you get acid rain and growth reduction. The sweet spot interacts in complex ways with other nutrients and growing conditions. I have little doubt that S deficiency or excess would affect growth ring dendrothermometry.

Common sources of SO2 have risen in the last decades, from sources such as combustion of dirty pyritic coal and smelting of sulphide mine ores. I cannot see the logic of assuming that CO2 and methane are the main culprits when SO2 has a similar ability to disturb. It might be the case that SO2 has been studied, but in casual reading I gave not seen it mentioned apart from the context of aerosols, Richard Lindzen style.

“[Mann’s] decentered methodology is simply incorrect mathematics.”

[sarcasm on]But just because it is “simply incorrect” doesn’t mean you can’t do it that way, right? [\sarcasm off]

What a surprise, none publish with him. Or at least not activly collborate on research papers.

You should not stick your hand into the lion’s cage.
You should not stick your finger into the fan.
You should not pour gasoline on the fire.
You should not leave a loaded gun where little children can get at it.
You should not jump out of an airplane without a parachute.
You should not make jokes about bombs while in line at airport security.
AND
You should not use “strip bark” samples for temperature reconstructions.