Reply #16: thanks hatrack!

[Lisa]

I didn't know about the 1.1 million-year core -- just the 700-800 thousand year ones. That's great! I can hardly wait to see the temperature isotope info and the trace gas breakdown.

Re: the Medieval Warm Period -- here is the NOAA page. They question the concept of a "global or hemispheric" climate shift during that time (as you say, more of a regional thing).

http://www.ncdc.noaa.gov/paleo/globalwarming/medieval.html

I have heard that there are some authors who have proposed it was caused by a solar cycle, or ocean thermohaline circulation, but I don't have the latest info on that.

One of the things the paleoclimate guys who gave the talk last week were grumbling about, was how the records in North America and Europe don't match up exactly.

As far as how well the different proxy data sources match up within a region ... sometimes there are some issues with exactly which variable is being measured (start of growing season, amount of erosion, shortages of soil moisture, etc.), but often the matches are surprisingly good.

As hatrack said -- they've got a whole range of things to look at, including ice cores, sediments (both freshwater and marine) which contain the fossils of pollen and diatoms, and tree rings. There are also other neat sources, like buried packrat middens, which occur in some places. I'm always amazed by how creative people get, to find data sources. Medieval harvest records, church documents on births/deaths, and even illustrations in prayerbooks have been suggested (e.g. the amount of clear sky, snow cover, and types of crops being grown).


Re: the Year Without a Summer -- it's possible that Al Gore's book, coming out in April, might talk about this. He mentioned it several times in "Earth in the Balance", and I wouldn't be surprised if he decided to return to the topic, to incorporate new information.

AngryAmish -- Another book which you might enjoy is David Keys's "Catastrophe" (recommended to me by a classical archaeologist, so the Roman stuff at any rate seems to have withstood her critical eye). It looks at other historical climate shifts which may have been related to volcanic activity.