Mark Colvin reported this story on Tuesday, February 18, 2014 18:22:00

MARK COLVIN: "There have always been tough times and lush times", said the Prime Minister Tony Abbott yesterday when asked about drought and climate change.



But the Bureau of Meteorology says 2013 was Australia's hottest year on record. And few scientists now doubt that that is the result of man-made climate change.



That includes some former sceptics in the scientific community who formerly doubted whether climate modelling could be trusted to forecast warming.



Among them is one of Australia's most respected agricultural scientists, Melbourne University's Professor Snow Barlow.



I asked him if it was fair to call him a former climate change sceptic?



SNOW BARLOW: Just a sceptical scientist. I wasn't a sceptic about the amounts of CO2 that we were putting in the atmosphere.



MARK COLVIN: But you were sceptical about the effects or the projected effects?



SNOW BARLOW: Yes, yes.



MARK COLVIN: Over what period have you changed your mind? And how have you changed your mind?



SNOW BARLOW: Two things have occurred. One, with the passage of time - and you will recall that it's really in the late '80s through the '90s and into the '00s - that global temperatures have increased quite considerably. So the evidence in my mind has begun to accumulate.



And also, at the same time, these computer models have got better. Various queries that other naturally sceptical scientists have raised about clouds, about satellites, have been answered.



And so I now have, you know, much more confidence in those. But a large degree of that confidence is around just observing what I see and observing what the impact of these increase in temperatures is on biological systems.



MARK COLVIN: So I won't ask you to comment on one particular heatwave or one particular bushfire or one particular flood. But are you saying that, overall, the number of heatwaves, bushfires, floods has grown and will continue to grow?



SNOW BARLOW: Particularly heatwaves.



We know that when you look at the way you calculate temperatures, as you move it up a degree - and the climate in Australia has actually moved up by 0.85 of a degree centigrade in the last 50 years - you move the distribution of temperature. That means that you get more events, very hot days. In other words: heatwaves. And not only individual days that are over 35, or in some areas 40, but sequence of days.



So instead of having an isolated day, you may have three or you may have five. And individual occurrences of that is what we call weather, of course. But when you put them all together and you see what the model is projecting, they paint a very convincing picture.



MARK COLVIN: So the models predicted more extreme events and we're getting more extreme events?



SNOW BARLOW: Yes. I should clarify: the moisture events are perhaps more problematic in terms of the models. There is not a high confidence at present about what the changes in rainfall will be.



But what there is some confidence there about is that as you move to higher temperatures, actually the atmosphere holds more water. So that when it does rain, those rainfall events are more intense and you probably get a bit more. So those things that lead to floods, you know, there's a good scientific explanation of that.



MARK COLVIN: You work in agriculture. What would you be saying to Australian farmers now?



SNOW BARLOW: For example, the industry that I've worked the most in which relates to climate change is the wine industry, the growing of grapes. And we have shown quite convincingly and published these papers in Nature, showing that vintages in Australia have moved forward - in other words earlier - by something like a day a year over the last 25 years.



And so there are some places in Australia where vintages now are somewhere between 20 and 30 days earlier.



MARK COLVIN: But yesterday the Prime Minister was asked about climate change in Australia and he said, "If you look at the records going back 150 years, there have always been good times and bad times and farmers ought to be able to deal with the sort of things that are expected every few years."



You are saying that things are not going the way they were 150 years ago or even 50 years ago?



SNOW BARLOW: I think those broad comments deny the detail.



I think when you look at the impact of these heatwaves which, because the average temperature is higher, we can expect to get more of - and indeed we are if you look at the number of maximum temperature records that were broken in our hottest year on record, 2013 - and if you look at the rainfall patterns, what people forget in that is: there have been droughts before and there will be droughts in the future, but what we call the evaporative demand - in other words, the amount of water that the atmosphere requires from the plants in order for them to stay alive - increases as the temperature goes up. So that what it means is: these droughts can be more intense when the ambient temperature is higher.



So certainly there have been droughts but you've got to look into the detail, of which climate scientists do, to tease out what is actually natural variability, which none of us deny, and what is that extra variability and extra intensity that comes from global warming and climate change.



MARK COLVIN: Professor Snow Barlow from the University of Melbourne's School of Land and Environment.