"No need to worry" was the consensus of the United Nations Climate Conference which closed in Berlin in early April. However, we do have cause for concern about carbon dioxide buildup and global warming and on Earth Day 1995 it is appropriate to explain why.
Commencing in the late 1950s, scientists at the Mauna Loa carbon dioxide observatory noted annual fluctuations in atmospheric gases coupled with a disturbing increase with time. Other observatories confirmed that rising carbon dioxide levels were global. The initial reading was 315 parts per million by volume By 1989 the carbon dioxide levels had risen to 355 ppm/v; today they are at 360 ppm/v.
To resolve whether this trend is not part of some short-term fluctuation we have to look at natural archives in the geological and biological records of our planet.
In polar regions and on high mountains hexagonal snow crystals gradually melt and recrystallise trapping atmospheric gases as minute bubbles in glacial ice. We have the ability to drill into ice, to pull cores thousands of metres in length, and to extract and analyse bubbles from different depths. The Antarctic Siple and Vostok ice-cores illustrate why alarm bells should be ringing.
The Siple ice-core records carbon dioxide levels over the past 400 years, when carbon dioxide remained about 280 ppm/v from the 1600s to the first half of the 1800s. After 1850 the line diverges, rising steeply to the present What happened in the mid-1800s to cause the change in slope? In simplistic terms it can be summed up in three words: the Industrial Revolution.
The steam engine was the principal culprit as it was used to create the material wealth seen in the mid-Victorian era. Steam machines were exported to all parts of the world Many used wood, a few used oil, but the vast majority used coal. Fossil fuel combustion produced carbon dioxide and the world's atmospheric change was registered as increased carbon dioxide levels in the global ice- record. Modern lifestyles in the First World have continued and accentuated the trend.
Is the Siple core a peculiar short-term aberration? Certainly not, and confirmation comes from the 2,083 metre ice core from the Vostok station, a record which goes back over 200,000 years. This covers the warm interval of the last 10,000 years (the Holocene); "the last ice-age" (the Wisconsinan); the warm period before this (the Sangamonian interglacial) and the glaciation before that (the Illinoian). Humans only reached an agrarian and limited urban stage of development in Holocene time, so for most of this period processes were in operation without undue human influence on natural systems.
The Vostok core shows low carbon dioxide levels (around 200 ppm/v) during the cold, glacial stages and higher carbon dioxide levels during the warm interglacial stages. How high during the warm periods? Interestingly, with the exception of a small "spike" which reached nearly 300 ppm/v the average is around 280 ppm/v, the same figure seen in the Siple ice-core prior to the Industrial Revolution.
The difference between global carbon dioxide levels during the glaciations and the interglacials was 80 ppm/v. Today levels are at 360 ppm/v - a rise of 80 ppm/v beyond the pre-Industrial Revolution levels and equal to the natural variation between glacial and interglacial conditions.
Increased carbon dioxide levels will mean an increased global greenhouse effect and atmospheric warming. The questions are by how much, when and how rapidly? This is the scientist's Achilles heel, where big business and the politicians take advantage of the uncertainty factor inherent in science.
However, we can take a further look at the geological record during the last interglacial and see how conditions differed from the present.
Evidence in ice cores, deep sea records, fossil animals and plants and stratigraphy illustrate disturbing events during the Sangamon. Hippopotamuses wandered in northern England and lions and hyaenas roamed Trafalgar Square in London. Giant sub- tropical tortoises inhabited central Illinois and plants such as Osage Orange grew in southern Ontario, Sea level was five metres above present level and global climate was 2 degrees Cels ius warmer than today. Remember that funny little "spike" in the Vostok core that went up to nearly 300 ppm/v? Remember that we are now at 360 ppm/v?
How rapidly can such a change take place? Fossil beetle research in Britain suggests that a 6 to 8 degrees Celsius mean annual temperature change could happen in less than a century. Recent work on Greenland ice cores suggests that such a change could take place in a decade.
The mixing of a warmed atmosphere with a warming ocean and the shutting down of ocean circulation will take a little while, but is it already underway? The last three months have produced satellite images of the East Antarctic Ice Shelf disintegrating, news of the death of thousands of penguins in Antarctica, dying seals on the coasts of Namibia and the demise of Pacific salmon. Are these all warning signs of some major change? Let's hope that we have not already pulled the trigger.
Alan V. Morgan
P.S. Just in case you were wondering. 1 ppm of CO2 is equivalent to 2 X 109 tonnes of carbon. 109 tonnes is 1,000 million tonnes; so 2 x 109 tonnes is equivalent to 2 billion tonnes of carbon).
(Alan Morgan of Waterloo is a professor of Earth Sciences at the University of Waterloo, He is one of the editors of WAT ON EARTH and was Global Change Coordinator at the Geological Survey of Canada from 1990 to 1992).