Annual Dinner and Awards
Is Greenhouse all Hot Air? A Short History of Planet Earth
Professor Ian R. Plimer, Department of Earth and Planetary Sciences, University of Melbourne.
Date: Thursday, 28 February 2002
Time: 6:00 for 6:30 pm
Venue: Holme and Sutherland Room, Sydney University
In more recent times, there has been debate about greenhouse, a phenomenon of the atmosphere. Greenhouse gas emissions trap heat in the lower atmosphere and the resultant surface warming of the Earth is called the greenhouse effect. Greenhouse gases do not warm the surface directly, the atmosphere must heat up first. If there is no prior warning of warming in the lower atmosphere, then there can be no consequent greenhouse effect attributable to it.
For 80% of time, Earth has been a warm wet greenhouse planet. The history of Earth shows that climate, sea level, life and the atmosphere have always changed. They continue to change. If there was not sea level change, climate change, mass extinctions of life and changes to the atmosphere of Earth, then life on Earth would indeed be doomed. Earth is dynamic, the rates of change are variable and the lithosphere, hydrosphere, atmosphere and biosphere all interact. Maybe the global warming of the 20th century is just a measure of variability on a dynamic evolving planet or an actual measurement of an orbital change in 1976-1977.
Current public political concern about global warming and sea level change are blissfully unconstrained by an understanding of the history of planet Earth. We live in the last days of our normal ration of 10 000 years of benign climate in a 100 000 year cycle driven by orbital changes. The orbital driver of our current greenhouse/icehouse cycle is well past its zenith and summer reflection of solar energy at higher latitudes of the Northern Hemisphere is now waning. The Armageddon we humans face is not a pleasant greenhouse warming but a bitter and prolonged icehouse. The 14th century AD was our wake up call.
Report on the General Monthly Meeting
by Edmund Potter
This was the title of the address given to the Society by Professor Ian Plimer (Department of Earth and Planetary Sciences, University of Melbourne) at its Annual Dinner at the University of Sydney on February 28 last.
In the time available to him (ca 4.75 x 10-5 years), Professor Plimer, a distinguished geologist, covered the time since the first running water appeared on earth and sustainable life began (2.4 x 109 years ago). Our speaker deftly judged he had little time to fully justify the chronology, choosing instead to immerse his listeners in a deluge of past events and their dates, all in a lively style guaranteed to keep us alert (if not aghast at what we had missed).
For example, of the 13 pieces of Mars found on earth so far, one hit a dog in Egypt in 1908 (your reporter does not believe we were sold a pup on this one). However, the speaker went on playfully to suggest Martian DNA could be so widespread that some of us might be sitting next to one (if so, then your reporter married her - vive la différence!).
A fearsome emphasis in Professor Plimer's address was the terrestrial recurrence at intervals of 108 to 109 years of major extinctions of life forms. Such havoc happens mostly when massive lumps of big-bang debris coincidentally cross our orbit or catch us up, but extinctions can also follow after continents collide or split, or when countless cubic kilometres of earth’s magmatic interior burst out violently enough. Any tick of the clock could presage another dinosaur-type disaster, with minimal warning to begin scanning our neck of the woods (as it were) for iridium and start the countdown. At least, we were told, bacteria are the great survivors, and our bodies are 18% bacteria (if there is a non sequitur here, then our speaker was blameless).
Professor Plimer concluded with a quick-fire account of the recent past (say AD), prefacing our prospects with the dictum that changes in earth's orbit cause cyclic climatic changes. So, 1.8 × 104 years ago, glaciation reached its zenith, but icehouse gave way to greenhouse 3.3 × 103 years later, with sea-level raised 150m. Although icehouse then made a comeback, the last of the BC millennia have been warmer than now. We weathered an episode of volcanic gloom with matching refrigeration in 535 AD or so. Then we endured a so-called "little" ice age from 1280 to about 1920, then ice cap melting to 1940, followed by ice-cap growth in the 1960s. Then, some time in 1976-1977 we actually measured an orbital lurch (forgive the digression, but your reporter wonders if this is what he felt on the 17th storey of the San Francisco Hilton on the evening of July 3, 1976, the day before nationwide bicentennial celebrations).
Professor Plimer ended his address almost reassuringly, saying he doesn't worry about greenhouse, but fears that from about now for several myriad years to come we would be wise to make the most of our dying days of warmth.
The Society's President, Mr David Craddock, requested Dr. Edmund Potter to propose the vote of thanks to Professor Plimer, and the replete but attentive audience endorsed this proposal by acclamation.