In April, the UK Information Commissioner's Office ruled that Queen's University Belfast must hand over data obtained during 40 years of research into 7,000 years of Irish tree rings to a City banker and part-time climate analyst, Doug Keenan. Professor Mike Baillie, the man who collected most of that data, called the ruling a "staggering injustice". He explains his opinion below.

I regard myself as a chronologist and a dendro-catastrophist; in particular I wish to link the tree-ring and ice core chronologies so that we can view some historical events, such as those around AD540 or 44BC, in human records, in tree-ring records and in ice core records of atmospheric chemistry. My early work was as part of a team involved in constructing a 7,000-year oak chronology at Belfast to allow calibration of the radiocarbon timescale. Since then I have built further chronologies and have studied some extreme events initially indicated by the Irish trees.

To put the record straight, I am neither a climatologist nor a dendro-climatologist. I have no academic stance on human-caused global warming except that, as a scientist reviewing the issue from an evolutionary perspective, if humans are even partly the cause of the warming since 1990 then we are already doomed as a species. I agree with Doug Keenan (the man who placed FOI requests at Queen's University Belfast asking for my data) that the issue of the Medieval Warm Period (MWP) is of critical importance at the present time. In a nutshell, either the MWP was warmer than now and we are in with a chance of surviving long enough to do something about climate change, or the MWP was cooler than now and we are probably due for rapid extinction.

In the 1980s we supplied our modern oak data (available at www.noaa.gov) to the Climatic Research Unit at the University of East Anglia. Work by the dendro-climatologists there gave rise to two papers Dr Keith Briffa and colleagues that convinced us that British/Irish oak was not a good subject for the reconstruction of instrumental-style temperature and rainfall records. Thereafter, at Belfast, we gave up any hope of contributing to the issue of climate change using tree rings. Recently a paper by Dr Garcia-Suarez (I am a co-author) on Irish trees and climate records shows results compatible with that research. It confirms that it is very unlikely that past temperatures can be reconstructed from Irish oaks. I recently stated that our Irish oak data has never been used in climatic reconstructions. It turns out I was wrong on this point. I did not know that the US climate scientist Professor Michael Mann had used a few of our oak records in a 2008 publication. I was not aware of his paper, nor of the use of the data. While this seems to be regarded by some members of the public as criminal (not to have read every paper on climate reconstruction), my reply is, why should I have known about it? I am not a climatologist. I have little research interest in present climate, only in trying to understand aspects of the past (as my publication list for the last several decades shows).

I consider that our raw tree-ring measurements should not have been released following an FOI request. I know the Irish data better than anyone else; particularly the highly disparate nature of the samples before the year AD1700 (variously from historic buildings, archaeological sites, lake margins and peat bogs). It is unlikely that these ancient woodland, forest or bog trees would have the same response to climate factors (such as temperature or rainfall) as current living oak trees. Worse still, living parkland oaks in Ireland are much wider ringed than any of the ancient oak populations. This is almost certainly because modern oaks on walled estates are probably imported stock, brought in from the 17th century onwards by landowners who wished to beautify their estates with large oaks. Even worse than that, although ancient bog oaks occur across Northern Europe, there are no good examples of oaks currently growing on raised lowland bogs anywhere. So it is essentially impossible to find out exactly what such oaks were responding to.

These latter observations mean that even if a climate-calibration exercise had been successful (comparing oak growth with modern instrumental records), it is unlikely that any attempt at interpreting the climate response of the more ancient Irish oaks would be meaningful. That is my considered view, though doubtless few will accept it.

Finally, regarding intellectual property and the release of data under FOI, when a dendrochronologist measures the widths of the growth rings in a sample, he or she has to make multiple decisions with respect to the starts and ends of the rings, problem rings, and so on. Repeated measurement of the same sample, will not give exactly the same measurements. The number of rings must be the same, but the actual measured widths will not be. This means that the ring pattern of a tree-ring sample carries the "intellectual fingerprint" of the dendrochronologist who measured it, every bit as much as this text carries my intellectual fingerprint. In my opinion, tree-ring patterns are therefore intellectual property and should not be handed out as if they are instrumental climate data.

• Prof Michael Baillie retired as a paid academic in 2005 before the current FOI issue began. He now holds an Emeritus position at Queen's University Belfast where he pursues research on chronology and mythology with a particular interest in sorting out the likely effects of volcanoes from those of comets or other extraterrestrial vectors.

* Individual tree ring-width data is available from 12 modern oak sites in Ireland, namely Ardara, Baron's Court, Breen Wood, Caledon, Cappoquin, Enniscorthy, Garryland Wood, Glen of the Downs, Killarney, Loch Doon, Rostrevor and Shane's Castle. Individual tree data is also available for seven English and Scottish sites.