Suppose that during the Medieval Warm Period, Earth was 1°C warmer than today. That would imply that the tipping point is more than 1°C higher than today’s temperature. For Earth’s temperature to increase 1°C might take roughly a century (at the rate of increase believed to be currently underway). So we would not have to be concerned about an imminent disruption of the climate system.
Finding out how warm the Medieval Warm Period is thus of enormous importance for the study of global warming.
It turns out that global (or at least hemispheric) temperatures are reflected by the climate in western Ireland (for a short explanation of that, see my site). Trees grow in western Ireland, of course, and each year those trees grow a ring. Thick rings indicate climate conditions that were good for the trees; thin rings indicate the opposite. If many trees in western Ireland had thick rings in some particular years, then climatic conditions in those years were presumably good. Tree rings have been used in this way to learn about the climate centuries ago.
Queen’s University Belfast has data on tree rings that goes back millennia — and in particular, to the Medieval Warm Period. QUB researchers have not analyzed the data, because they lack the expertise to do so.
They also refuse to release the data. The story is scandalous.
I have been trying to obtain the data via the UK Freedom of Information Act since April 2007.
(Nature.com had a brief piece about my FOIA request. The piece has statements from QUB that are dishonest: see my comment posted there. Statements from QUB therefore should be checked. My site has source documents for its claims.)