John Murphy (Lowe, Australian Labor Party, Parliamentary Secretary to the Minister for Trade) Share this | Hansard source

I note the interjection by the shadow parliamentary secretary for infrastructure, roads and transport, who is at the table, but he should listen to what I am going to say. Although there was a decline in average global atmospheric temperatures between January 2007 and January 2008—and I hope he is listening—the long-term average, taken between 1850 and 2007, shows an inexorable increase punctuated by minor excursions of higher and lower average temperatures. This a fact. Further, the temperature difference between 1998, which was an exceptionally warm year characterised by an intense El Nino, and 2007, a year of cooler than average temperatures affected by a strong La Nina that brought up cold waters from the bottom of the Pacific Ocean, is also put forward as evidence for global cooling. Unfortunately for the sceptics, and I presume the shadow parliamentary secretary fits into that category, these kinds of fluctuations are the product of complex weather cycles and have occurred frequently in the past and do not represent anything more than a random departure from the steady escalation in average global temperatures, which is not in dispute.

The flux of energy emitted by the sun that is received by the earth, termed the solar constant, has been monitored for many years and has been found to be stable at 1,360 watts per square metre with a variation of plus or minus 1.3 watts over a regular 11-year cycle. If a reduction in the sun’s radiated output was responsible for the recent 0.6 degrees of cooling, the solar constant would have to have fallen by 13 watts per square metre—a decline of a magnitude that has never been observed. Similarly, if an increase in the flux of solar energy were to be the cause of global warming then the required change in the solar constant would have been very significant and obvious. The solar constant has not changed sufficiently to affect global temperatures since highly accurate satellite based measurements began in the 1970s, yet global temperatures have continued to rise in line with the growing concentration of carbon dioxide in the atmosphere.

Cosmic rays—or high energy subatomic particles—that bombard the earth from the distant reaches of space have been suggested as an extraterrestrial agent responsible for global warming. The proposed mechanism by which cosmic rays influence earth’s climate is somewhat tenuous and depends upon the unproven promotion of cloud formation by cosmic rays. The number of cosmic rays striking the earth is reduced by a more intense solar magnetic field, which occurs at times of higher solar activity. Theoretically, the earth could be warmed by this process because a lower number of cosmic rays would mean that there could be fewer clouds to reflect solar radiation. Yet, to date, there is no convincing evidence that this effect has any significant influence upon the earth’s climate.

The last claim that I wish to discredit is the proposition that the carbon dioxide that is accumulating in the atmosphere has arisen from natural sources. Extensive and long-term measurements show that, although the exchanges of carbon dioxide between the atmosphere, the oceans and the biosphere are very large, the emissions from natural sources have, in the past, been in equilibrium with natural sinks. Ancient atmospheric samples trapped in Antarctic and Greenland ice cores show that carbon dioxide levels have fluctuated slowly between 180 and 300 parts per million for the past half-million years and have only seen a rapid climb to the present level exceeding 380 parts per million since the beginning of the Industrial Revolution. The combination of these and many other strands of evidence demonstrate conclusively that fossil fuels have been the largest single source of increasing atmospheric carbon dioxide levels over the past 150 years. Sceptics like those who sit opposite can now resort only to falsehoods or extremely remote or, at best, tenuous speculation to account for a process that is best understood by the simplest explanation: that is, that human activities have reached such a scale that we—yes, humans—have now become the primary agent of change on the earth’s surface and that some of these activities, in particular the annual release of around 30 billion tonnes of carbon dioxide into the atmosphere, have started to change the climate. That is why the National Greenhouse and Energy Reporting Amendment Bill 2008 is an important instrument in our fight against climate change. Climate change is real. Action is required and the Rudd government is committed to addressing the problem.

See this speech in context