Institute of Advanced Studies

Grand Swings in Climate Change: Greenhouse Gas Trends across Time

Climate is an integral element of Earth’s history. For more than a million years it has been alternating between long glacial periods, with massive ice sheets covering much of North America and Europe, and shorter warm interglacial periods with ice sheets restricted to Greenland and Antarctica. We are living in an interglacial – a warm phase that started more than 10,000 years ago, and should, by now, be trending once again toward cooling and beginning glaciation. But this interglacial appears to be different. Why?

One idea is that increasing greenhouse gas concentrations may have begun with the early agricultural revolution. Around 7,000 to 5,000 years ago there was widespread burning and clearing of forests for cultivation of wheat and other cereals, and a rapid growth of rice cultivation. The combined effects of the early agricultural and the recent industrial revolution have produced concentrations of greenhouse gases that far exceed levels found during comparable stages of previous interglacials.

This lecture reviewed the evidence for greenhouse gas trends in this interglacial, compared to earlier interglacials, and then describe experiments with climate models that address three questions:

1. what would the climate be now without the combination of the proposed effects of early agriculture and the well-documented effects of modern industry and agriculture?
2. what is the relative importance of the two revolutions in influencing our climate? and
3. what natural processes and feedbacks may have amplified these trends ?

What lessons can we learn? If early agriculture practiced by several million people disturbed the natural rhythm of climate, how much greater and more certain is the modern impact of several billion people? Are we finally beginning to understand the magnitude of our actions - literally altering, for the first time, the grand swings of climate that have governed our natural history for more than a million years and throughout the period of hominid evolution?

About the Gentilli Memorial Lecture

The University of Western Australia established this memorial lecture in 2005 to honour the memory and intellectual legacy of an influential and long serving scholar who devoted 60 years of his life to this institution. Joseph Gentilli (1912-2000) commenced teaching at the University soon after arriving in Fremantle from Italy in 1939, and continued to be actively involved with the Geography Department until 2000.

During his long and distinguished career at the University of Western Australia, Joseph Gentilli helped to bring about a comprehensive understanding of the climates of Australia.  In addition to his many other contributions, he wrote about “the selective or “greenhouse” effect of the atmosphere” more than 50 years ago (A Geography of Climate, The University of Western Australia, 1952), and more than 30 years ago was calling for a “synchronoptic dynoclimatography” to illustrate how climate patterns were changing (Australian Climate Patterns, Nelson, 1972).

Tuesday, 10 March 2009