Friday, February 26, 2010

The February Storm

On the weekend of the 13 and 14 February, Canberra enjoyed heavy rainfall, with 107.4 mm falling in the space of 50 hours or so.

Since then, I have been tracking inflows into Canberra dams to see how it compares with past inflows.

Today, I believe we have gained the vast majority of that inflow - we might get another 50 megalitres or so over the next couple of days, but probably not that even that much.

From this 107.4 mm of rainfall, Canberra dams received 8,756.6 megalitres of water. By comparison, from the 442.4 mm of rainfall in 2009, Canberra dams recieved 43,240 megalitres of water. This was a terrible year for inflows: 23 per cent of the long-term average.

However, if we recieve the same amount of rain this year as we did last year, and the inflow from that rainfall matches in a megalitre per millimetre sense what went into Canberra dams from the February storm, the percentage would drop below 20 per cent to 19.2 per cent.

Now, this storm was at the tail end of summer, so it can be assumed that the ground was thirsty for water. It may also be the case that big storms provide a lower level of inflow than smaller yet more frequent bursts. However, at this point, the storm has not provided much reason to be hopeful about the future of inflows in Canberra.

It of course remains to be seen whether we will get more rain this year than last year - the odds favour it, as currently (because of the storm) we are about 30 mm above average for the year so far. I will continue to track rainfall versus runoff for the course of this year to see if I can work out any patterns (unlikely from a year of data, but if they are strong they might show up.)

Monday, February 22, 2010

Why we lost

Those of us on the side of the debate who believe:

1.) the earth is warming;
2.) this warming is caused by increasing CO2;
3.) this increase in CO2 is being caused by human activity; and
4.) this warming will be bad for us and for many species;

have lost the debate, at least in the short term, and that may well mean that we have lost it for the long term - at least for the sake of the suffering of many people and many animals.

Why did we lose?

People often talk about people like Carl Sagan and Richard Dawkins, and wonder why we cannot come up with climate science communicators of their calibre. The problem here is not really to do with the calibre of the people - there are some excellent communicators of climate science; you do not have to look far to find them. The problem is to do with the comparative difficulty of explaining and selling - yes, it is about selling -cosmology, evolution and climate science.

Cosmology and evolution can both in their own ways be inspiring. They are answers to deep questions at the core of what it means to be human. They are able to be built as powerful and, more importantly, positive myths - even more powerful because they are true. Who has not looked up at the stars in wonder? Who has not thought about the diversity of life on this planet of ours and wondered where it came from? With these powerful stories as a base, a skilled communicator can move the world.

But climate science does not connect with humanity in the same fashion. We are not the end point in the story - we are star stuff and we are an endpoint of billions of years of the evolutionary process, but we are not 'climate stuff'. There is no place in the climate story for humans ... except as the villains of the piece. And there is the nub. Humans do not want to be the villains. We want to identify with the good guys; we want to be inspired.

Thursday, February 18, 2010

Submission to the ACT Legislative Assembly

A submission that I made to the ACT Legislative Assembly has now been made publicly available. It is here:

There are two mistakes in it, annoyingly. I forgot to alter 'one per cent' to 'five per cent' in the section on global warming and Canberra daytime temperatures. And in the references section, there is a typo, with 'factormation' instead of 'information' - maybe it will become a new word, though. ;)

I also did not explain something that I should have done. This was that, while changes in global temperatures cause changes in local temperatures and while changes in local temperatures cause changes in local rainfall, it is difficult to link changes in global temperatures with change in local rainfall *directly*. This is because there are many other factors. Given R^2 values of around 40 per cent for the two known relationships, there will be at best a 16% value for the correlation between the two more distant numbers - and it is likely to be much lower than that.

More to be added.

Tuesday, February 9, 2010

"2030 climate change may have already occurred in the Canberra region" ...

This is a submission to the ACT legislative assembly by the managing director of ACTEW Corporation, Mark Sullivan. It contains much of what I have already posted on. However, there is one key paragraph:

"It would be prudent in a risk management framework for Government to identify policies and implement programs based on the assumption that 2030 climate change may have already occurred in the Canberra region."

I wonder if the public of the ACT understands this; I wonder if the federal government understands this. We know that the federal opposition sure doesn't ...

The step change in WA

The above article demonstrates that climate change has already affected precipitation in Australia. Whether Canberra has been similarly affected is not known. But as I have previously reported the CSIRO believes, based on the statistics, that it is possible that Canberra has undergone a step change in precipitation.

They are understandably cautious: scientists usually are, and scientists working for government agencies even more so. But I think that the statistical evidence is very clear indeed. While I am unable to detect the mechanism by simply using statistical data, it is possible that a mechanism similar to that discussed in the article above is operating here.

Climate change is not some distant threat. Climate change is here.

Monday, February 8, 2010

Assumptions regarding Canberra rainfall predictions

I have made the prediction on this blog that Canberra inflow - the water that ends up in dams - will effectively drop to zero by around 2017. It should be noted that this is not a solid number - there is a considerable statistical range over which this could happen. But 2017 is the mean.

There are a number of assumptions underpinning this prediction. Any one of those assumptions might be wrong.

The basic argument is that rainfall is declining due to climate change and that declines in rainfall cause declines in runoff. This decline has been observed.

There are three sets of arguments running here.

Argument 1

Premise 1: Climate change will continue.
Premise 2: If climate change continues, daytime temperatures in Canberra will continue to increase.
Conclusion 1: Therefore, daytime temperatures in Canberra will continue to increase.

Argument 2

Premise 3: Increases in daytime temperatures reduce rainfall.
Premise 4: Reductions in rainfall lead to reductions in runoff.
Conclusion 2: Increases in daytime temperatures reduce runoff.

Argument 3:

Premise 5: Daytime temperatures in Canberra will continue to increase.
Premise 6: Increases in day time temperatures reduce runoff.
Conclusion 3: Runoff will reduce.

(Note how conclusions 1 and 2 became premises 5 and 6.)

There are other assumptions here - the premises have not been spelt out completely. The main assumptions involve the rate at which day time temperatures will increase and the rate at which those temperature increases will cause rainfall, and hence runoff, to decline. The rates predicted are based on empirical observation.

The problem with this is that the future may well differ from the past in this respect. Just as it is possible that we have undergone a step change in climate here in Canberra, so it is also possible that we will undergo another one soon.

Further, it is possible that there is a limit at which daytime temperature ceases to become the dominant driver of rainfall. Thus, a one degree rise in temperature in the future may not have the same effect as a one degree rise in the past.

So, my prediction could well be wrong. But that is how science advances: by linking empirical observation to a theoretical model and then testing that theoretical model against further empirical observation. At the moment, my theoretical model - based in empirical observation - is predicting an end to Canberra runoff by 2017.

Friday, February 5, 2010

The graphs

The first graph is for rainfall versus inflow for the last 14 years (23 years worth of data). As you can see, the R^2 value is .93, which is a very good fit.

The second graph is for rainfall decline over time for the same period. Again, there is a very good fit.

I have extended the graphs forward so that the conclusions of the previous post can be seen. By 2017, rainfall will drop below 450 mm. By that point, runoff will effectively be zero.

Worse than I thought

This report from ACTEW (Australian Capital Territory Electricity and Water) is essential reading for anyone interested in the future of Canberra's water supply.

Of particular note is this:

"Whilst global warming progresses proportionally to the build up of greenhouse gases in the atmosphere, it can result in rapid ‘step’ climate changes in a particular region. It is possible that the recent drought represents a shift in climate for Canberra. The past 5 to 10 years are clearly the most severe long-term dry period in the 1871 to present extended historic record inflow sequence."

I have looked at the data on inflows in this report at page 23 (PDF page 25) and tried to estimate the figures from the graph. While I may be out somewhat, it will not be by all that much (although I wish that they had included the data or at least a reference to it). When graphing the values for the last little while (14 years of 10-year averages, which includes 23 years of data) against the rolling 10-year rainfall figures for Canberra, I found that every 1 mm decline in the rainfall average means around a 70 megalitre decline in inflows. This means that when the 10-year average rainfall drops to around  450 mm, inflows drop to zero. Zero.

If the current trend in declining rainfall continues, this point will be reached by 2017, eight years from now. You heard it here first.

Again, the error margins here are reasonably large because of the autocorrelation in the 10-year averages. However, this is significantly sooner than my previous estimate of 2030 for zero inflow into Canberra dams.

Thursday, February 4, 2010

An image showing the last two years of Australian rainfall

Note the low rainfall in the south-east of Australia and the high rainfall in the north - this is the pattern of rainfall that climate change models predicted would occur as the world warmed. We are experiencing climate change now... 

Wednesday, February 3, 2010

Richard B. Alley: The biggest Control Knob: Carbon Dioxide in Earth’s Climate History (written summary) (video) (I now cannot get the video to work - I will keep the link here, though, and check back in a few days)

A fantastic summary of why we know CO2 causes warming, why we know the climate sensitivity is high and why we know that this century is going to be hot unless we do something ... fast.

Tuesday, February 2, 2010

Testing hypotheses

I have presented the hypothesis on this blog that Canberra will become a desert by mid century if greenhouse gas emissions are not dramatically reduced.

A test of whether a claim is scientific or not is whether there are empirical observations that would demonstrate that the claim is unlikely to be true. In the case of my hypothesis, there are indeed empirical observations that would demonstrate this, and I will list some of them here.

1.) Obviously, if the five-year average rainfall has not fallen to 250 mm or lower by 2050, my hypothesis would be 'unlikely to be true'. I would suggest that there is some wiggle-room here - if five-year average rainfall has fallen to 253 mm, then I would still claim that my hypothesis is likely to be correct. However, if we set 265 mm as the cut-off, that makes things very clear.

2.) The above empirical observation cannot be made until 2050, which is a fair way off. There are, however, observations that can be made sooner that would demonstrate that the claim is unlikely to be true. A year with rainfall of 850 mm or above would be just such an empirical observation. Further, I would suggest that for every five years that passes, we can reduce this by 30 mm. In other words, for the years 2010-2014, if any one of those has 850 mm of rainfall or above, my hypothesis is unlikely to be true; for the years 2015-2019, if any one of those has 820 mm rainfall or above, my hypothesis is unlikely to be true.

Five years out of 70 have had rainfall over 850 mm, so on average one year in 14 should meet that criteria.

It should be noted that these are the current numbers - they will not increase, but they may decrease as more data comes in that shows definitely that the variance in annual rainfall has declined - at the moment, these figures rely on the current observed variance. By way of an explanation, currently, the standard deviation is about 170 mm, meaning that 95 per cent of the time the rainfall will be within the range of the average plus or minus 340 mm.

3.) If any five-year average is 670 mm or greater. This figure will again decline by 30 mm for every five years that passes.

21 five-year periods out of 66 have had an average of 670 mm or greater, so one in three.

4.) If any 10-year average is 600 mm or greater. This figure will again decline by 30 mm for every five years that passes.

44 10-year periods out of 61 have had an average of 600 mm or greater, so more than two in three.

This should be sufficient for now. There are other possible criteria, such as rainfall in multiple five-year periods in a row, but they are mostly covered by the 10-year average situation.

Monday, February 1, 2010

Local short-term drought or long-term regional climate shift?

One question is thrown up by my analysis of Canberra rainfall over the last little while: isn't this simply a local drought that will pass at some point? If it is a local drought that will pass, as droughts do, then my analysis for the long term is flawed and we are likely to be having more rain in 2050 than we have had over the last few years.

However, there are two major lines of evidence that point to our recent weather ('recent' being weather over the last 15 years or so) being a long-term climate shift rather than short-term drought.

The first is the relationship between Canberra day-time temperature and rainfall. As temperature rises, rainfall decreases. This relationship has held for the entire period of record. We know that the global climate is warming and that locally we will continue to experience rising temperatures - indeed, we know that Canberra is warming and will continue to warm at two or more times the global average. So, if the relationship between temperature and rainfall holds - and the evidence is that it will - rainfall will continue to decline.

The second line of evidence is the unprecedented nature of the current rainfall deficit. There has never been a drought of this magnitude or of this length of time in the 70-year record. Indeed, prior to this drought, only eight five-year periods had qualified as drought periods. This drought has covered 6 consecutive five-year periods (which is, for clarification, 10 years in total). The drought during WWII covered 4 consecutive five-year periods, or eight years in total. And there is no sign that our current drought is going to end this year.

To compare further, the average yearly rainfall during the WWII drought was 530 mm. For the current period, the average yearly rainfall has been 519 mm. The current period has also had a much lower variability in yearly rainfall - all years in the decade have had below average rainfall except one, while in the eight years of the WWII drought, two years had above average rainfall.

The evidence is that this is not simply a local short-term drought. Rather, what we are experiencing is a long-term climate shift that is affecting not just Canberra but Victoria and the whole of southern NSW. Climate change is here.