Australasian Science: Australia's authority on science since 1938

Climate Change or Natural Variability?

Image of barometer

The long-term trend in annual rainfall for Australia from 1900 to 2009 is upwards at a linear rate of 6.33 mm/decade.

By Robert E. White

Meteorological records since the 1950s reveal a decrease in rainfall that is consistent with anthropogenic climate change, but a different picture emerges when looking at records since 1900.

Robert E. White is Professor Emeritus of The University of Melbourne’s School of Land and Environment.

The full text of this article can be purchased from Informit.

The Fourth Assessment Report of the Intergovernmental Panel on Climate Change concluded that the increase in the Earth’s surface temperature during the second half of the 20th century can only be simulated by models that include anthropogenic forcing, and not just natural factors. However, the report acknowledges that there are difficulties in simulating and attributing observed temperature changes at smaller than continental scales, expecially when attempting to model the amount and distribution of rainfall.

As part of the Australian Climate Change Science Program, CSIRO and the Bureau of Meteorology (BOM) scientists have modelled a number of attributes of the Australian climate at subcontinental scales, and concluded in their State of the Climate statement that, relative to the period 1981–2000, “decreases in rainfall are likely in the decades to come in southern areas of Australia during winter (and) in southern and eastern areas during spring”.

The statement makes the point that “models make assumptions about future events such as CO2 emissions, and are designed to paint a picture of a series of possible future states based on known facts... as opposed to observations which are accurate measures of an event that has already occurred”. This latter statement should be examined more closely because records of events can be used selectively.

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The full text of this article can be purchased from Informit.