thanks, found it.
Abstract
A 538-yr tree-ring chronology and reconstruction of June temperatures were developed from living and dead Larix dahurica trees. The samples were obtained near the lower Lena River in northern Siberia. Dendrochronological techniques were used to estimate the ages of establishment and mortality of Larix dahurica on the presently treeless uplands and to determine the establishment dates of living trees in the lowlands. The 20th century may have experienced the greatest prolonged period of high June temperatures over the past 538 yr. In contrast the greatest prolonged period of cold appears to have occurred during the first half of the 19th century. It was during the 19th century that the uplands lost much of their tree and soil cover. Recruitment of trees occurred in the lowlands during the 20th century, but trees have not been able to recolonize the uplands, possibly due to the lack of suitable soil.
http://www.jstor.org/pss/1552005
Still, no one has overcome the problem of determining temperature in any given year, but we can, in fact, tell you what the Sunspot count was. That's because the ratio of carbon 14 to carbon 13 varies directly with the number of Sunspots.
That feature, in turn, could give you a general idea of overall climate since we have historic records of colder temperatures during long periods of Sunspot minimums, and vice versa ~ but Mann wouldn't want to prove that himself ~ 'cause it'd say "Hey, bro, it do be cold doncha' know and there's almost no Sunspots".
You can use tree ring data to demonstrate widespread climatic problems ~ e.g. the cold spell for a couple of years right at the beginning of the Dark Ages (circa 535 AD). Trees don't always grow better, faster, bigger and wider when it's warmer, but if it gets colder all at once, leaves don't form and bingo, tree rings don't grow very much at all.
Part of what's going on with these Siberian trees is that we don't know much about the environment of any particular tree.
“greatest period of prolonged cold during the first half of the 19th century.”
Don’t forget “the year with no summer” after Tambora in 1815. Temperatures were colder for several years after. Also Cosiguina in Central America was a big one in 1835. Might be others, no time to look now.