50 U3A members attended this excellent lecture at the Torch Theatre as guests of the Pembrokeshire Earth Science Schools Trust (PESST) on Monday 18th Nov. The speaker was Dr Carrie Lear, Reader in Geology at U.C.Cardiff. Her presentation on a perspective of Climate Change had a profound message for all of us.

50 million years ago in the Eocene Times the World was a much warmer place than today. Fossil evidence shows us that the ancestors of animals we now associate with the tropics roamed in the tropical forests covering southern Britain. Forests grew in northern Siberia and Antarctica where now it is covered by Tundra and Ice Sheets. Techniques involving the examination of the detailed chemistry of microscopic single cell organisms called Foraminifera, now entombed in ocean bottom deposits, have revealed to Geologists a full record of carbon dioxide levels and temperatures over the last 50 million years. This shows that the level of the greenhouse gas carbon dioxide has declined causing the average World temperatures to decline by about 10C.

This decline reveals three distinct chilling periods. The first was 34 million years ago when mountain glaciation occurred in Antartica. The second some 20 million years ago when an ice cap formed over the whole of Antarctica. The third when the Pleistocene Ice Age began 2 million years ago. We (homo sapiens) are just living in one of the warmer interglacial periods of this Ice Age.

The causes of these changes in carbon dioxide and World temperature are complex, but a major factor is the effect of Plate Tectonic Movements that have left Antarctica isolated over the South Pole, while the southern continents of South America and Australia moved north, leaving an open Southern Ocean surrounding Antarctica. This isolation enabled Antarctica to develop extreme cold conditions which have impacted on the climate of the rest of the World.

However, since the beginning of the Industrial Revolution two centuries ago the level of carbon dioxide in the Atmosphere has increased and now stands at approximately 400 parts per million. The highest it has ever been before in the last 800.000 years is 300ppm. Monitoring of this level of carbon dioxide in the Atmosphere reveals that the rate of increase is accelerating which in turn is increasing Global Warming. Warmer conditions, apart from changing our weather and climate conditions, mean that glaciers and ice sheets will melt.

The Greenland and West Antarctica Ice Sheets are now unstable and melting. The quantity of water locked in these ice sheets will mean significant rises of sea level. The melting of the Greenland Ice Sheet will produce a sea level rise of 6 metres and that of West Antarctica a further 8 metres. If the East Antarctica Ice Sheet melts a further 60 metre rise of sea level will occur. This would drown those parts of Pembrokeshire below 240 feet above sea level. As for the rest of the World, coastal lowlands, major river lowlands and their cities would all be flooded completely.

The major questions for all of us are how long will it take for this to occur and have we the power and will to reverse the process?

Graham Goodeve – 19th Nov 2013