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

In response to the previous speaker, the member for Canning, it is important to put a price on carbon. Despite the scaremongering by him and his colleagues, the Leader of the Opposition and his fellow deniers on the science that warns of the disastrous consequences of global warming, the latest reports of the rapid decline in Arctic sea ice further reinforces the concerns of climate scientists and responsible governments around the world about the destructive effects of carbon dioxide emissions and why it is so important to put a price on carbon.

For some time, climate scientists have warned that, unless carbon dioxide emissions are reduced, the world risks passing through irreversible climate tipping points that will push the world's climate from the current stable state to another less desirable state—for instance, from present conditions where the world has polar ice caps to one where there are no polar ice caps and where, according to the United States Geological Service, sea levels would be 80 metres higher. By definition, once a climatic tipping point is passed, returning to current conditions will be impossible because tipping points are self-reinforced by positive feedback, the well-understood process familiar as the howl that emanates from a public address system when the microphone is brought too close to the loudspeakers.

Positive feedback in climate change is of great concern because, like a screeching PA system set off by moving the microphone, what may seem to be inconsequential changes are rapidly amplified and fed back into the climate system, driving it to another less desirable stable state. For instance, positive feedback has been shown to drive the climate from ice ages to conditions similar to those that prevail at the present time, when cyclic changes in the earth's orbit initiate the switch from glacial episodes to interglacials every hundred years or so.

In 1941, the Serbian geophysicist and astronomer Milutin Milankovic published a paper entitled Canon of Insolation of the Earth and Its Application to the Problem of the Ice Agesin which he showed that the driving force behind the cycles of ice ages and interglacials were regular variations in the intensity of solar radiation received at higher latitudes. Such was Milankovic's prestige that, despite the fact that his country had been invaded and was then occupied by Germany, German scientists assisted in the publication of this important document. According to Milankovic's theory, the earth should now be cooling and beginning to enter the next glacial period. Yet what we see, as the CSIRO said in its 2012 report on climate, is that average global warming temperatures are increasing—

A division having been called in the House of Representatives—

Sitting suspended from 12 : 00 to 12 : 11

Each decade since the 1950s has been warmer than the previous decade. Ice-core evidence, which shows that carbon dioxide levels follow average global temperatures from ice-age frigidity to warm interglacial conditions, is frequently used by deniers to argue against the fact that carbon dioxide is driving global warming. In fact, this process is actually a clear demonstration of the operation of a positive feedback in the climate, wherein an initial warming caused by orbital changes is amplified by the build up of atmospheric carbon dioxide, driven from the oceans by increasing temperatures.

To digress, it is a well-known principle of chemistry that warmer water will dissolve less gas than colder water. In the regular switch from glacial to interglacial periods, the initial warming at high altitudes, identified by Milankovic, is reinforced by accumulating atmospheric carbon dioxide that further drives up temperatures by positive feedback, until an equilibrium similar to present day conditions is reached. Positive feedback initiated by global warming is now evident in the Arctic Ocean, where the decline in sea ice initially caused by increased local temperatures has been reinforced by darker seawater absorbing more solar heat, thus accelerating a further decline in the ice cover. As temperatures increase, more ice melts, more sea water is exposed to the sun, and since 2007, the difference between summer and winter ice cover is now more than one million square kilometres and growing.

New evidence presented by Professor Tim Lenton of the University of Exeter at the Planet Under Pressure Conference in London at the end of March this year, suggested that we are close to or may even have crossed the tipping point in the Arctic, with the area of summer sea-ice cover having reached a record low that may be the prelude to ice-free summers across most of the Arctic ocean. Drastic changes in the northern hemisphere weather systems are expected to follow the development of an ice-free Arctic ocean. Some palaeontologists believe that the Neanderthals were driven to extinction by climate change and despite the population imagine of Neanderthals, recent discoveries suggest that these close relatives had a complex culture, comparable to modern humans. Yet they are, as we well know, extinct., the well-known NASA scientist and climate change adviser to US presidents, seriously warns that unless we drastically curtail carbon dioxide emissions, the same fate may await us, the last surviving human species. (Time expired)

See this speech in context