I enclose a copy of the Society's lecture programme for the 2001/2002 session.
The first lecture will be on Thursday 20th September at 8.15 pm in the Crypt Room at St John's Church, Church Row, NW3. It will be on Railway Signalling by R S Wyatt.
There has been much debate on the subject of "global warming" and how the activities of industrialised countries are affecting the weather. But as more research is carried out into the complex events which drive our weather systems and control our climate, we are beginning to discover hitherto unknown cyclic events. These events have the potential for far more dramatic climate changes than anything mankind can do to alter the climate.
Recent research by scientists from the University of Copenhagen has uncovered what appears to be a very worrying cyclic event. An event which could, if it proves to be correct, have a devastating effect on the climate of western Europe. If one looks at a globe of the Earth and compares the latitude of, say, London with that of Moscow and parts of Siberia, and then we compare the average Winter temperatures of these locations, we can see at once something strange. Whereas the Winters in Siberia are viciously cold, western Europe enjoys a far more temperate climate. This is due to the warming effect of the Gulf Stream, a vast ocean current which conveys warm sea water up from the tropics along the eastern sea-board of the United States across the north Atlantic and thence to our shores. This current of warm water has the effect of warming the air above it by an average of 15 degrees C. during the Winter months. It is the reason why it is still possible to grow palm trees, which are tropical plants, in some Devon and Cornish seaside resorts. Without the heating effect of this benign current our Winters would resemble those of Siberia!
Fortunately for us, the Gulf Stream has been comforting our shores for about 16,000 years but, according to the research by the University of Copenhagen, the Gulf Stream has in the past ceased to circulate and, on these occasions, it has stopped flowing quite suddenly.
This discovery was made by examining ice cores drilled in Greenland. Core samples of the Greenland ice contain sample of frozen atmosphere laid down thousands of years ago; by analysing these samples it is possible to discover the temperatures endured by northern Europe in the distant past. These temperatures are ascertained by calculating the ratio of two isotopes of oxygen: oxygen 16 and oxygen 18. In very cold conditions the percentage of oxygen 18 is greater. The Copenhagen team have discovered that prior to about 16,000 years, the oxygen 18 content was far greater and for a considerable period prior to this the ratio of 0-16 to 0-18 was subject to wild fluctuations, suggesting chaotic climate variation. It is believed that the reason for this is that the Gulf Stream stopped flowing.
The Gulf Stream conveys warm water from the tropics and flows northwards. Warm water is less dense and forms the surface layers. As it warms the air above it, this mass of water gradually loses heat and by the time it reaches the north polar ice cap, it has cooled. The fresh water freezes out and the heavier salt water sinks. It is this convective process which drives the current. In order to maintain this current it is necessary for the Earth to have a northern polar ice cap.
The Earth's northern ice cap has no land mass beneath it. It is composed wholly of floating ice with an average thickness of 3-4 metres. For many years now the thickness and extent of the polar ice has been monitored by Earth-orbiting satellites and by the sonar of nuclear-powered submarines, which regularly patrol beneath it. There is now no doubt that our northern polar ice cap is shrinking, both in thickness and extent. Computer predictions indicate that it may disappear entirely in a matter of decades. When it does, the Gulf Stream will cease to flow, with dire consequences for the climate of western Europe.
As the Copenhagen team have shown, this has occurred before in the distant past, so we cannot blame it on man-made global warming. This discovery is another example of the cyclic nature of the Earth's dynamic systems, systems which are still not fully understood.
Another example of mechanisms which can affect our climate but are not fully understood is the greenhouse effect caused by methane. Molecule for molecule, methane is 25 times more potent than the carbon dioxide of which we now hear so much. Moreover there are 10 trillion tons of it buried in the ocean floor, twice the amount of all known coal, oil and other fossil fuels. This could play havoc with the world's climate if it were to escape into the atmosphere! William Reeburgh of the University of California and other geochemists demonstrated in the 1970s that methane-producing microbes were continually producing the gas deep below the sea bed, but found that it had all but disappeared in the mud near the ocean floor. They suggested that other microbes might be eating it up as soon as it arrived. It would also explain why carbonates found there were low in the ratio of carbon-13 to carbon-12, just as methane is. Methane-eating bacteria were well-known in fresh water, but seemed to need oxygen; there is none however in the ocean sediments.
Evidence is now mounting that the microbes responsible are archaea; these superficially resemble bacteria but are a separate domain of life. Proof of this has now been reported by a team (V J Orphan, C H House, K-U Hinrichs, K D McKeegan and E F DeLong) in Science of 20th July this year using secondary ion mass spectrometry and other techniques. They showed that the archaea cells were highly depleted in C-13 and must have lived on methane; they also formed a symbiotic relationship with sulphate-reducing bacteria.
These methane-eating microbes now look profoundly important to the planet's carbon cycle. Hinrichs and Boetius estimate that they devour 300 million tons of methane each year, about equal to the amount we inject into the atmosphere by agriculture, landfill and fuel burning. It may be speculated that the evolution of these microbes may have saved the planet from a run-away greenhouse catastrophe in its earlier days with a reducing atmosphere, as happened to Venus.
Peter R Wallis
Last updated by Julie Atkinson 11-Sep-2001