Monday, February 12, 2007

Australia's climate is changing: it always has

Tim Flannery has done it again. Recently given the status of Australian of the year for his scare mongering climate doomsday talk, he wrote this piece for the Age.

He suggests that current rainfall trends in Australia support the idea that farmers in the drought stricken south should move further north where the rain is plentiful.

“On the face of it, current rainfall trends would support this idea because southern Australia is receiving ever less rain, while larger and larger amounts are falling over the north, particularly the north-west.”

“During the past 50 years, the shift in rainfall has been substantial, with some areas of southern and eastern Australia receiving 250 millimeters less rainfall than they did back then, while parts of the north-west are receiving 250 millimeters more.”

He continues on saying:

“But before making large investments in the transfer of agriculture north, we would be wise to ask what is causing these changes in rainfall, and to try to determine whether the trends will continue.”

Obviously a great idea. Neville Nicholls as commissioned by the Australian Greenhouse office conducted a study and concluded that

“there is strong scientific evidence that rising temperatures are being caused by an increase in greenhouse gas concentrations.”

So a study funded by the greenhouse office concluded that greenhouse gases were the cause. Amazing!

But in the same paragraph suggests that

“These gases are also thought to be causing at least part of the rainfall decline across southern Australia, though land clearance and natural variability of rainfall may also be having an impact”

So in other words, we have no hard proof of why the rainfall has changed, if of course it has. It could be a number of different things. But let’s jump to conclusions as Flannery does and suggest that

“it is our human pollution — from sources as diverse as power plants, motor vehicles, and farms — that is contributing to the drying of our country and causing immense hardship”

Astonishingly, Flannery goes on to say that

“Astonishingly, given the huge impact that the loss of rainfall in the east is having on Australia, there have been no detailed Australian studies of the cause of this rainfall loss.”

What? So we have no significant research done in this area. But didn’t Flannery just conclude that power plants, cars and other evils are the cause? All based on “no detailed Australian studies”? Talk about jumping to conclusions.

Ok, so let’s do a simple analysis of the weather then. Once again as shown on the graph below, rainfall has been low in south eastern Australia the last 5 years, but not as low as it has been in the past. Last year south eastern Australia didn’t have a lot of rain, but in 1982 we had a lot less. And despite the last 5 years having limited drizzle, the period of 1940 to 1944 had less rain than what we are experiencing now. To me, that just means natural variability, and our statistical analysis proves it so (t = 1.29 p = 0.20).

But what of southern Australia? The graph below shows rainfall for all of southern Australia since 1900. Last year we didn’t have a lot of rain, but we still had 70 more millimeters than we did in 1940 and 64 more millimeters than we did in 1944. Looks like a case again for natural variability, although if you look hard enough you can see a slight increase in rainfall over the years. What does our statistical analysis say? Yes! Amazing. Our analysis suggests a statistically significant increase in rainfall in southern Australia (t = 2.06, p = 0.04) at the rate of an extra 0.44 millimeters per year.

So the south is getting more rain, despite not so in the last 5 years. Excellent news indeed.

Now let’s head to the north, and we can see from the graph below we get a lot more variation in the year to year differences. We had a whole stack of rain from 1997 to 2001 as well as from 1973 to 1976. There looks to be an increase in rainfall from about this period onwards, but let’s let the statistical analysis do the talking. And yes, we find a significant increase in rainfall across Northern Australia (t = 3.08, p = 0.003).

So what can we conclude from this? Well Flannery suggests the possibility that farmers spend millions relocating further up north to get more rain. And it seems that Northern Australia is getting more rainfall then previously, at a rate of an extra 1 millimeter per year. But what about the big dry down south? Well we proved that south-eastern Australia is not significantly drying up, and that southern Australia shows a significant increase in rainfall over the past 107 years.

Sure it’s been a bit dry in the last 5 years, but not as dry as it has been previously. But Tim Flannery is correct, our climate is changing. In fact, it always has done.


Alan Woods said...

Good ol' Flannery. He loves that line about 250 mm less rain in some parts of SE Australia. I had this letter published in The Age on the 31st of January in response to it:

Doctor, heal thyself

TIM Flannery writes that we must underpin our decisions regarding our future with good science. It would be helpful if he would do the same.
Flannery claims that parts of south-east Australia are receiving 250 millimetres less rain than 50 years ago, but analysis of the Bureau of Meteorology's records shows that the long-term trends for rainfall have changed only marginally and are much the same as they were for the early part of the 20th century.
Flannery also cautions that "some models show that global warming would cause northern Australia to become even drier and sunnier than it was in 1950", if Asia reduces its aerosol output. This implies that other models don't show this. Flannery would better serve the science by telling us what proportion of models predict drying and whether it is statistically significant.
Alan Woods, Kingsville

Enjoying your blog, Jonathan. Keep up the good work!

Agmates said...

G'day Jonathan,
Mate it's good to find your blog. I'm doing a series of articles on my blog agmates about "Climate Change" In tonights article I'll put a link to your post today.
It is scary how the spin doctors of climate change have got it into the Australian psychie that we humans beyond a shadow of doubt are causing climate change.
We need to keep blogging "the facts" to try and turn this sham around. My Blog address is
I'll link to your site could you please link to mine and we'll keep working on giving readers the facts to dispell the likes of climate change spin doctors like Tim Flannery.
Cheers - Steve

Dazza said...

Hi Jonathan,

I keep hearing about the so called 90% probability of climate change being man made as stated in the IPCC report summary. Can you explain in a statistical manner what is the true meaning of this and how they would come to this conclusion?

Hope this makes sense.


Jonathan Lowe said...

hi dazza, I would imagine that there is no statistical analysis that is made to come to the defining probability of "90% probability of climate change being man made". One could prove what percentage of temperature increase related to CO2 levels, but causation is a problem. I think it is basically made up based on the evidence at hand.

And if so, the null hypothesis has to be accepted as one normally needs less than 5% probability to prove the case. Hence if this 90% probability is true, we have to conclude that there is not enough evidence to prove that global warming is mad made.

Count Iblis said...

"One could prove what percentage of temperature increase related to CO2 levels, but causation is a problem."

Causation is no problem at all. It is just a matter of basic physics, see here

Jonathan Lowe said...

ahh climate modeling....hmm...need I reply? and the 90?

Dazza said...

Cheers Jonathan,
I glad I made sense to you with what I was trying to get at.