John Murphy (Reid, Australian Labor Party) Share this | Link to this | Hansard source

I join with you, Mr Deputy Speaker Slipper, and applaud the member for Aston for his contribution. Despite the relentless campaign of climate change denial orchestrated by the Leader of the Opposition, evidence for the baleful effects of unabated carbon dioxide emissions continues to accumulate along with the greenhouse gases produced by the burning of fossil fuels. Most recently Professor Julian Sachs from the University of Washington in Seattle and his colleagues from Princeton University have shown that the intertropical convergence zone, the band of rain that produces the annual wet season in Australia's north, is moving northwards in response to rising global temperatures that are, as is beyond reasonable doubt, being driven upwards by carbon dioxide pollution.

Present-day climate patterns such as El Nino and La Nina are well recognised; however, less well known is the band of heavy rainfall that circles the globe in the tropics and that moves to the north or to the south according to the seasonal angle of the sun. The area in which this rain band moves is called the intertropical convergence zone and the band's present average latitude varies across the globe from roughly 10 degrees north in the northern summer to three degrees north during the southern summer. The annual migration of the intertropical convergence zone greatly affects rainfall in North Australia and merging with the monsoonal circulation results in the tropical wet season that occurs at the same time as a the corresponding summer season of higher latitudes.

Professor Sachs and his colleagues have extensively mapped changing rainfall patterns in the tropical Pacific that have occurred over the past 1,200 years and have shown that small changes in greenhouse gas concentrations can greatly affect tropical rainfall. The evidence is taken from repeatable and independently verifiable measurements that have been made in many places across the Pacific that have in the past or that presently fall within the intertropical convergence zone. While it is obviously not possible to obtain records from the Pacific Ocean that cover the past 1,200 years there are sediments found underneath lakes on tropical islands that record the ratio of precipitation relative to the evaporation of lake water.

With the advice provided to me by a very respected scientist I will explain the method of obtaining measurements that can be used to infer past rainfall from tropical lake sediments. As has been understood since Berzelius's determination in 1826, water molecules are composed of the elements hydrogen and oxygen in the ratio of two atoms of hydrogen to one atom of oxygen, hence H2O. A proportion of hydrogen atoms approximately 0.03 per cent by mass is deuterium or heavy hydrogen that is almost twice the atomic weight of the more common lighter isotope. The means of inferring rainfall from earlier times depends upon this mass difference since the ratio of deuterium to the light isotope of hydrogen found in the lipids of algae that are preserved in lake sediments on islands has a linear relationship with the ratio of deuterium to the normal lighter isotope of hydrogen that was present in the lake water in which the algae grew. That ratio in turn reflects the ratio of precipitation to evaporation so that in areas of high rainfall within the tropical rainband the ratio of deuterium to the lighter isotope of hydrogen is low because water molecules containing the heavier deuterium tend to remain in the sea when water evaporates to form rainclouds.

Field measurements from the intertropical convergence zone have tracked the movement of the rainband over the past 1,200 years and show that a large shift to the north of about five degrees of latitude, or around 550 kilometres, has already occurred over the last 400 years. These measurements also show that during what is called the little ice age, between 1440 and 1850, the rainband's mid-line remained south of five degrees north, while under the present warmer conditions it varies between three and 10 degrees north and is moving north. Increasing temperatures resulting from greenhouse gas pollution threaten to move the mid-line of the rainband north by another five degrees by 2100, a shift that would have very serious consequences for the north of this country as the annual wet season could be greatly diminished in intensity. The evidence is before us and shows that unless we rapidly arrest the increase in atmospheric carbon dioxide by putting a price on emissions, these irreversible changes will seriously damage this country and the wider world. Doing nothing will never be an option. (Time expired)