Well I never! As I said “I suspect you could glean some idea of the weather of an individual year from our yields”, looks like someone tried something similar.

As to trees ring. Not sure anyone is trying to make out they are more than one of several available proxies? I also readily accept the MWP and LIA across Europe. I just doubt (i.e. I’m not certain – yeah, I know that heresy to some) they were global.

But, I’m not sure anyone uses barley yeilds to reconstruct past temperatures

Actually “grain” yields was one of the proxies Ruediger Glaser used in his book “Climate History of Central Europe”, published 2001.
He tried to “describe” the “weather” in Central Europe during the last 1.000 years using town chronicles, weather diaries, tree rings, grain and wine production, harvesting time, floodings…

He concluded that in the MWO we had “hot” summers and “cold” winters, with the “hot” summers primarily responsible for the overall “warm” climate.
While today we have generally “mild” summers and “mild” winters, with the “mild” winters adding a lot more to the average “warm” temperature.
With all in all roughly the same “average” temperature as during the MWO right now.
Although he cautions that this doesn´t mean that the issue of global warming should be dismissed.
(I should add that his data sets probably ended somewhere in the 1990s.)

Concerning tree rings.
He worked with the “Hohenheim Dendro research center” in Germany.
Quote from the book (my translation):
“Tree rings from “moderate” locations, which are typical for Central Europe except for the Alpes and some other hilly regions (Harz mountains, Black Forest region etc. in Germany) aren´t conclusive in “average” years. Because they don´t show a uniform growth of tree rings in those years. Only in years with extreme climate conditions is the tree ring growth “uniform” even in moderate locations. These “signatures” are called “Weiserintervalle” or “Weiserjahre”. Accordingly only these signatures were used in his research.”

Probably meaning that in “average” years other influences (location, soil, precipitation, human and animal actions, …) tend to “over-shadow” the temperature factor.

Wind speeds will affect the open field CO2 experiments most, as more wind will dilute the CO2 levels (that is the reason for planting hedges too!). That is less so for open top experiments, as CO2 is heavier than air and will be diluted only at higher wind speeds. And closed top experiments are of course not affected by wind.
On the other side, open field experiments are more natural for other constraints like rain, humidity of leafs and soils,…

The influence of CO2 from mulching obviously is for smaller plants, and specifically for plants where leaf forming is of importance (like salad, parsley, celery,…). The microclimate is important too: reduce wind speeds by planting hedges. I have done several experiments and it works…
For trees, the increasing CO2 levels probably play a role, if there are no other constraints. In many cases the lack of fertilisers may play a role too on poor soils. Together with more CO2, more nitrogen oxydes are emitted (and more ammonia from agriculture), which may give a boost in growth…

For the high North trees, the most important constraint probably is temperature (and humidity) in the growing season. The more intruiging it is that especially these type of tree series don’t show a post-1950/1980 warming. See e.g. the over 7,000 year series of North Finland at page 14/15 of Pages: No MWP, no LIA and a cooling after 1950…

No problem. It was just a small nitpick.\

The more general question is, do you accept that the rate of growth of plants has an inverted-U shape when measured against temperature?

Well, I could have worded it better I suppose. I had the ph measure in my mind.

Not to be picky, but isn’t the point of applying lime to reduce acidity, not increase it?

John writes: George Orwell was right. It is indeed possible to alter the present by rewriting the past. How nice that you put a spaghetti diagram of different studies in front of the Mann Hockey Stick in order to obscure it. You might not have noticed, but Mann (and mouthpiece David Appell) specifically deny that the Medieval Warm Period and the Little Ice Age were global climatic events. See my post Sci-Am: Mann and the Hockey Stick. So why the Mann Hockey Stick (obscured) is on a diagram marked with the MWP and LIA is beyond me.

In point of fact, if the accompanying text and conclusions still hold, please present any empirical evidence that rising carbon dioxide in the atmosphere causes rising temperatures. Note that I said empirical and not modelled.