Despite what you might hear in the media—and, indeed, what you heard in this chamber only a short while ago—climate change science has become less certain and gives us less reason to worry since the last major climate conference in Copenhagen six years ago.

Before I expand further on this, and because people are often asked to state their beliefs in this debate—I am not sure why in a policy debate that is necessary—I think it is pretty important that I state my beliefs up front, not that they count for all that much. Having read much of the science, I believe that carbon dioxide has a warming effect on the atmosphere. Taken alone, the best evidence suggests that a doubling of carbon dioxide in our atmosphere—what we are on track for—would lead to a one-degree-Celsius increase in temperature. Higher estimates are the results of second-round effects. The evidence for these is much more thin, and I will expand on that later, but the upshot is that we just do not know enough about these second-round impacts, because they are projections about a future world that cannot be measured.

I do not want to focus on my beliefs today. I want to focus on the facts and, given that those facts do not lead to conclusive judgements, what the appropriate policy responses are in the face of such uncertainty. What we can measure at the moment is how much temperature has risen for a given level of increase in carbon dioxide that we have witnessed. Over the past 18 years there has been an eight per cent increase in atmospheric carbon dioxide levels, yet there has not been a significant increase in observable temperatures.

There are five main datasets that measure global temperatures, two based on satellite observations and three based on surface or terrestrial observations. The RSS satellite series shows no warming for 18 years and eight months, and the UAH satellite data shows only a minimal amount of warming over that period. A linear regression trend of the mean of the surface based measures—the GISS, the HadCRUT4 and the NCDC measures—shows a warming rate of around one degree Celsius over the 18-year period. But this is far under, far below, the projections of climate models.

An eight per cent increase in carbon dioxide over the past 18 years might not sound like too much, but it represents a third—more than a third, actually—of the increase in carbon dioxide in the atmosphere since the industrial revolution. This is testament to the massive increase in economic growth in China, which has exceeded all expectations. Yet the fact that this strong economic growth and the consequent large increases in carbon dioxide emissions have not led to the kinds of temperature increases that were expected is a perplexing and troubling phenomenon for the conventional climate models.

That fact is not in contention. Indeed, because of that very fact, the recent IPCC report has revised down its assumptions about the sensitivity of the climate to concentrations of carbon dioxide. The fifth IPCC report, released last year, made many changes compared to the fourth assessment report, released in 2007 ahead of the Copenhagen conference. The most significant of these changes related to the equilibrium climate sensitivity, which is defined as a change in global mean surface temperature at equilibrium that is caused by a doubling of the atmospheric carbon dioxide concentration.

The IPCC fourth assessment report in 2007 concluded:

The equilibrium climate sensitivity … is likely to be in the range of 2 to 4.5°C with a best estimate of about 3°C, and is very unlikely to be less than 1.5°C. Values higher than 4.5°C cannot be excluded …

That was the story in 2007. Last year, the fifth assessment report concluded:

Equilibrium climate sensitivity is likely in the range of 1.5°C to 4.5°C (high confidence), extremely unlikely less than 1°C (high confidence), and very unlikely greater than 6°C (medium confidence).

The key points are that the IPCC has lowered the bottom of the likely range from two degrees Celsius to 1.5 degrees Celsius, and the latest report does not cite a best estimate, whereas the fourth report cited a best estimate of three degrees Celsius. The reason given by the IPCC for not estimating or citing a best estimate was that there was a large discrepancy between the observation based estimates of climate sensitivity and the estimates from climate models—the exact issue I was referring to earlier.

Those changes in the IPCC report were not unexpected. They were largely expected, given the evidence that was coming in. Indeed, the prominent science journal Nature, in 2013, before the IPCC report came out, said:
Unfortunately, one thing that has not changed is that scientists cannot say with any certainty what rate of warming might be expected, or what effects humanity might want to prepare for, hedge against or avoid at all costs.

A major reason for this uncertainty is that climate models make assumptions about the amount of increasing carbon dioxide levels that leads to increases in concentrations of other greenhouse gases, primarily water vapour. But this positive feedback, as it is known, from increasing water vapour is highly uncertain, as it is assumption based, and it ultimately drives the temperature estimates the models generate.

They are not observed results. They are projections based on a set of hypotheses, hypotheses that are legitimately made but must be tested. That is the ultimate way we do science. We test hypotheses. However, if, as seems increasingly likely, the sensitivity is at the lower end of the spectrum to carbon dioxide concentrations then large increases in carbon dioxide will result in much lower temperatures than expected.

It is the same story with extreme weather events and unreliable, circumstantial evidence. There has been much made in the media about these extreme weather events—cyclones, heatwaves, bushfires et cetera—and purported links to climate change, but, again, the evidence is highly uncertain.

By definition such events are hard to test, because they are so rare, which makes statistical testing difficult due to a small sample size.

Perhaps the world's foremost authority on these issues is Dr Roger Pielke Jr. He is a professor in the Environmental Studies Program at the University of Colorado. Using data from the IPCC, as well as his own and others' peer-reviewed scientific publications, he demonstrated quite conclusively in his book The Rightful Place of Science: Disasters & Climate Change that extreme weather events have not increased due to climate change. His analysis is actually backed up by the latest IPCC report on extreme weather, which states:

Long-term trends in economic disaster losses adjusted for wealth and population increases have not been attributed to climate change, but a role for climate has not been excluded …

Again, evidence is very uncertain in this field.

I only have a limited time available, so I want to just briefly comment on some of the other issues in climate change science. Recent research shows that Arctic sea ice and polar ice caps are not melting at 'unnatural' rates and do not constitute evidence of a human impact on the climate. The link between warming and drought is weak, and by some measures drought actually decreased over the 20th century. The best available data show sea level rise is not accelerating. Local and regional sea levels continue to exhibit typical natural variability, in some places rising and in some places falling.

Senator Wong:  "You just make this stuff up. You know better than the CSIRO?"

Through you, Madam Acting Deputy President, Senator Wong should be quite familiar with the fact that, in the Murray-Darling area, there is no evidence that drought has increased over that period. We had large droughts both at Federation and at the turn of the century, but in between we had record rainfalls, as we have also had very recently.

We do face incredible uncertainty about how the climate might be changing and about how sensitive it might be to carbon dioxide levels. We face uncertainty in many parts of our lives and we often do not know what action to take to mitigate the risks. I do not know when I am going to die, but I do have life insurance to mitigate that risk, in case it unfortunately occurs. But, if I received information that I am healthier than I thought, that I do not have as much to worry about, of course I would change how much insurance I buy or make sure the costs of that insurance were not greater than the costs of the actual risk that I faced. The risk of dangerous climate change has reduced since Copenhagen. That is confirmed by the IPCC and by the actual evidence on temperature data, extreme weather events, drought and sea levels. Accordingly it holds that the policy action we should take in response should be less ambitious, less costly and less binding than what was envisaged at Copenhagen six years ago.

I support the moves to make aspects of any new international agreement non-binding and reviewable. There is no clear global solution to this issue. We should instead let nations make their own decisions about how to respond in a cooperative and flexible manner. The evidence that there is dangerous climate change is not as strong and we should therefore not impose large costs on the global economy, especially for developing countries. In addition, rigid policies that are hard to adjust as the evidence becomes more definitive, one way or another, are unwise.

So proposals to introduce economy-wide carbon taxes or emissions trading schemes are not the right solutions. Proposals by the Labor Party to slash our carbon dioxide emissions by almost half in less than 15 years are ridiculous and put at risk major industries and thousands of jobs. Worse, they will do nothing for the environment during this time but cost our economy a fortune. The right approach is to act in a no-regrets manner. We should adopt policies that will have other benefits independent of their impact on greenhouse gases, that are agile and do not impose large costs or transition costs on our economy.