Sir Peter Medawar won the Nobel Prize for Medicine in 1960. His field was immunology and his work on the mechanisms by which the human body rejects foreign tissue revolutionised techniques for skin grafting and made possible the later developments in organ transplant. But Medawar was also much admired for his thoughtful reflections on the whole philosophy of science and he summed up his views in a book in 1967: "Among scientists there are collectors, classifiers and compulsive tidiers-up; many are detectives by temperament and many are explorers; some are artists and others artisans; there are poet-scientists and even a few mystics."
Paleoclimatologists, on first consideration, might seem to fall into the "classifiers and collectors" category, but you will find that they must be detectives and explorers, too. They look underneath the most unlikely stones in search of the climatic past and rummage endlessly in nature's oldest rubbish bins for bits and scraps of information to complete their theories. Their times are ancient times, the early days of civilisation and prehistory, long before there were any written records of the weather.
Luckily for them, the weather leaves its footprints on the sands of time. Layers of sedimentary rock, for example, contain hidden information about the climate which prevailed around the time they settled. Pollen samples, too, show the range of vegetation at the time, and buried fossils indicate the insect life; both are related to the climate. And tree-rings are another fruitful source of information, varying in width depending on the rainfall and the temperature in the year in which they formed.
If you have an interest in such matters, you will wish to hear the tale that Dr Overpeck will tell. Jonathan Overpeck of the University of Colorado is head of the paleoclimatology programme of the National Oceanic and Atmospheric Administration in the US. At 6 p.m. on Monday he will deliver the 1999 John Joly Memorial Lecture in the Walton Lecture Theatre, TCD.
He promises to tell us, inter alia, how newly-available data clearly show that the Arctic, and the northern hemisphere in general, have experienced warming during the last century that is without precedent in the last millennium. He also has evidence in his portmanteau to prove that the so-called "Medieval Warm Period", a long spell of genial conditions in the Middle Ages, was not a phenomenon of the global happening but a local happening confined to Europe.
His lecture is entitled "A Paleoclimatic Perspective on Global Warming". My informant tells me helpfully that "the level of presentation will be suitable for a general, educated audience, i.e. pretty well all the readers of The Irish Times".