## Townsville’s record-breaking 2015 rainfall

I have been grumbling for months about how dry Townsville has been in the last year, and the annual figures are now in: 2015 was the driest year on record, with just under 400mm compared to our average of 1135mm and our highest-ever of 2400mm. We have just continued the pattern by completing a dry January, 77mm compared to an average of 270.

My figures are from the BoM’s Climate Data Online for Townsville airport, here (I have rounded them off to the nearest whole millimetre). Looking at the annual rainfall totals in that table, a pattern pops out: four-digit and three-digit totals don’t alternate randomly but come in clusters, 3-5 of each at a time. For instance, 2001-06 were all below 1000mm, while 2007-12 were all above it. Extracting the first and last columns and colouring the totals blue for wet years and brown for dry years (see table at left; click on it for a larger version) makes the pattern more obvious, and highlights one other quirk: a run of dry years is sometimes interrupted by a single wet year (e.g. 1968 and 1981) but the converse isn’t true.

I also divided the range of annual totals into three: close to average (1000 – 1300 mm), wet years (more than 1300) and dry years (less than 1000). Colouring them appropriately brings out another feature, showing just how rare an “average” year is: only one year in five is within that zone.

Monthly rainfalls also vary wildly. I could repeat the same exercise for  (e.g.) January rainfalls, where the average is 270mm but the actual figures vary from a mere 9mm to 1142. We can’t even say that a wet January is particularly likely to be followed by a wet February and March. Sequences like 85 – 549 – 53mm (2002) and 19 – 316 – 73mm (2003) are not uncommon.

In fact, we have to realise that an average month or year is not at all normal.

### Climate is what we expect, weather is what we get

So can the statistics tell us anything useful at all? Well, yes. They can obviously say things like, “Yes, 2015 was much drier than usual. It wasn’t your imagination.” They can also warn us not to expect an average month or year, something that long-term residents are vaguely aware of but many newcomers are not.

More subtly, they can warn us that we are getting a run of extremes and should be concerned by them. As Hansen warned us some time ago, every broken record carries the fingerprint of climate change – not necessarily caused by climate change, but made more likely by climate change.

They can show us, too, how our climate is changing over the long term – and those trends are likely to continue into the future, over at least a similar time-frame. “Climate is what we expect, weather is what we get,” (the quote is well known but its origin is obscure) and in those terms it’s clear that we need to look at periods of more than ten years.

Fortunately, we have done that – well, the BoM has, and has made the data available to all of us online. In particular, their trend maps make long-term changes beautifully (scarily?) clear. Here, for instance are the national rainfall and average temperature trends since 1970.

Food for thought – especially the extreme drying trend down the East coast, where most Aussies live. For more detail, follow my link to look into different regions, seasons and data sets.

As for Townsville, all we know is that we don’t know what to expect. The BoM made some educated guesses for the Townsville Bulletin’s January 4 article about our meagre 2015 rainfall but most of the article was concerned with very short-term forecasts. The BoM’s Outlook page suggests that the North will be drier and hotter than average in the next few months, Feb-April, but we shall have to wait and see.

## Defining a rapidly changing climate

If the climate is changing, what is it that’s changing? Climate, they say, is what you expect, while weather is what you get. But if climate is changing, how do we know what to expect?

That may sound flippant but it has become quite a serious question in climate science circles of late, for two reasons: communicating climate science to the public, and dealing with the statistical problem of defining a moving target.

On the first question, for instance, we have a typical member of the public asking on the RealClimate open thread“One thing that has confused me is how long it takes for weather to become climate.”

One of the regulars replied: “WMO (World Meteorological Organization) states that climate is 30 or more years of weather data.” Another backed him up, saying, “The traditional answer is 30 years or thereabouts.” ‘SecularAnimist’, another regular, answered at greater length:

I think this question is increasingly irrelevant, and the “traditional” answer is becoming obsolete.

The question was relevant when we were asking whether the various atmospheric conditions, processes, events and patterns of events that comprise “climate” are in fact changing, and wanted to know over what length of time we’d need to observe those phenomena as ever-changing, short term “weather” to be able to conclude that the changes are sufficiently long-term to be considered “climate” change. But we already know that the climate is changing, and will continue to change, as a result of our CO2 emissions. We don’t need 30 more years of observations to tell us that, now.

And the “traditional” answer is obsolete because it presumes that the Earth’s climate is sufficiently stable, and changing so slowly, that it really does take 30 or more years of observations to detect any long-term, large-scale change. That’s no longer the case, because the climate system is being driven to change more rapidly and extremely than it has ever done in human history. It’s unlikely to take another 30 years for the American midwest to become desert. It’s unlikely to take another 30 years for the Arctic sea ice to disappear completely during summer — with all of the prodigious effects that implies.

There is every reason to expect that permanent, large-scale, dramatic changes, which cannot reasonably be called anything but “climate change”, may now occur on time scales of a few years, rather than a few decades, as would have been expected in the pre-AGW world.

The more technical problem with the definition of climate is that weather needs to be averaged over enough annual cycles to iron out the bumps caused by specific weather events (that’s where the ’30 years’ comes from) but if, for instance, the averages of the 1980s, 1990s, and 2000s are successively quite different from each other then a ‘climate’ defined by the 1980-2010 average becomes meaningless.

Should we just average over a shorter period, then? No, because known multi-year cycles such as El Nino will distort the result too much. As far as I know, the experts are still working out what to do about that. Meanwhile they tend to define our baseline climate by the period from 1951-1980. James Hansen, whom I have mentioned before, presents the reasons very sensibly in a very recent discussion of his recent ‘climate dice’ paper:

Studies of climate change generally use some base period to define an average climate and calculate “anomalies” relative to that average, i.e., climate anomalies are the deviations from that average climate. In our papers we used 1951-1980 as the base period.

Global temperature change over the past century (Fig. 1) helps us discuss possible effects of the choice of base period. Our choice of 1951-1980 as a base period has several merits:

1) The period 1951-1980 is prior to the large warming of the past few decades. If we wish to examine the effect of that global warming on climate, we must compare with the climate that existed prior to that warming.

2) The 1951-1980 period has the best global data coverage and can best characterize climate variability. Spatial coverage of data was poorer at earlier times.

3) 1951-1980 was the base period used by the National Weather Service and other researchers when we made our first analyses of observations and climate simulations. For comparison with these early analyses and climate simulations we should use the same base period.

4) Many of today’s adults, baby-boomers, grew up during 1951-1980, so it is recent enough for many people to remember what the climate was like.

The whole discussion is well worth reading, since it presents the key findings of the longer and more technical paper in a very approachable way. Download it (pdf) from here.

## Extreme weather around the world

For a while now the climate scientists have been warning that global warming isn’t simply a matter of the weather getting a little warmer everywhere. Rather, the warming will vary from place to place and be accompanied by changes of weather patterns, especially rainfall. That is already happening. I have mentioned extreme weather events here before over the last year or so, and in fact the last few months have seen a cluster of extreme events which are causing great suffering across the Northern hemisphere.

We know that none of these can be ascribed to climate change with any certainty but there is a growing body of knowledge (e.g. IPCC, Climate Communication) which shows that we can confidently give the odds that a particular event would have happened without global warming, and the experts are quoting high odds against any of these happening under our old weather patterns. The combined odds against all of them happening by chance are infinitesimal.

The silver lining to this litany of disaster is that ordinary people are beginning to see for themselves that weird things are happening to their weather and are more willing to acknowledge that climate change is indeed here already, that it is looking scarier every year, and that we really should try harder to avert it.

Smile: In what seems like poetic environmental justice, a brown coal mine in Victoria’s Latrobe Valley has also been flooded after unusually heavy rain.

Don’t smile too broadly: James Hansen, one of the world’s pre-eminent climatologists, has warned that the future he predicted is here here already and it is worse than he expected, sooner than he expected – almost entirely because of extreme weather events:

In a new analysis of the past six decades of global temperatures, which will be published Monday, my colleagues and I have revealed a stunning increase in the frequency of extremely hot summers, with deeply troubling ramifications for not only our future but also for our present.

This is not a climate model or a prediction but actual observations of weather events and temperatures that have happened. Our analysis shows that it is no longer enough to say that global warming will increase the likelihood of extreme weather and to repeat the caveat that no individual weather event can be directly linked to climate change. To the contrary, our analysis shows that, for the extreme hot weather of the recent past, there is virtually no explanation other than climate change.

The rest of his Washington Post article is here and if you want the whole scientific  paper you can get it – free – here.

## Remembering the floods

I wrote about extreme weather events and their connection to global warming two and a half months ago and a small coincidence leads me to revisit the topic. Today has been chosen as the day of remembrance for the disastrous SE Queensland floods a year ago, and a link on RealClimate took me yesterday to a paper by eminent climate scientist James Hansen which touches on something I’ve been thinking about for some  time: the fact that climate change should already be apparent to ordinary people.

First, the floods. Wikipedia has a good overview here with plenty of links to further information and the ABC has put together a terrific gallery of flood photos here. There’s not much point in trying to add to that coverage here. The floods certainly qualify as an ‘extreme weather event’ and were recognised as such in the major global report State of the Climate in 2010 from NOAA and the Bulletin of the American Meteorological Society.

Hansen’s paper, Climate Variability and Climate Change: The New Climate Dice (November 2011) (pdf here) begins thus:

The “climate dice” describing the chance of an unusually warm or cool season, relative to the climatology of 1951-1980, have progressively become more “loaded” during the past 30 years, coincident with increased global warming. The most dramatic and important change of the climate dice is the appearance of a new category of extreme climate outliers. …

The greatest barrier to public recognition of human-made climate change is the natural variability of climate. How can a person discern long-term climate change, given the notorious variability of local weather and climate from day to day and year to year?

This question assumes great practical importance, because of the need for the public to appreciate the significance of human-made global warming. Actions to stem emissions of the gases that cause global warming, mainly CO2, are unlikely to approach what is needed until the public perceives that human-made climate change is underway and will have disastrous consequences if effective actions are not taken to short-circuit the climate change.

He goes on to show two kinds of systematic change in climate: the averages have shifted and, at the same time, the odds of extreme events occurring have increased dramatically. This, of course, is the significance of his title: the climate dice have been loaded (biased) by global warming. He presents details of the changes which have already occurred and notes that, “The climate dice are now loaded to a degree that the perceptive person (old enough to remember the climate of 1951-1980) should be able to recognize the existence of climate change.” In particular, people should be noticing that extreme weather is far more common than it ever used to be.

He doesn’t quite ask, “Why don’t they notice?” but the question hovers there, waiting for an answer.

I have been trying to answer it myself since a random conversation a year ago. I was chatting to a youngish, intelligent person with a degree in natural sciences and a job in  GBRMPA, which looks after the Great Barrier Reef. I was quite surprised to find that she had not actually observed the effects of climate change. Then I found that she had spent her first ten years on a Pacific island, her next eight in Sydney, and another eight or so here in Townsville, so she hadn’t actually been anywhere long enough to notice a change in that location.

As I thought about that, I realised that she has lots of company. There are far fewer people who might reasonably be expected to notice climate change than we might at first think. A quick estimate goes like this:

• Age group really has to be 40+, since anyone under ten in the early 1980s won’t remember the old norms. Change has occurred in the last thirty years, but it is the comparison with the pre-1980 baseline which makes it stand out strongly. That rules out more than 50% of the world’s population and perhaps even more than 50% of the world’s voters.
• But also, those people have to have been living in the same general area for 40+ years, or have returned to it after some time away, because no-one in California will say, “It wasn’t like this when I was a kid,” if they grew up in Normandy, Queensland or even Virginia. How many Westerners are that stable? 50%?
• Furthermore, the closer we live to nature, the more likely we are to notice its changes – but more and more of us are urbanised. Europe, Australia and the US are all more than 80% urbanised according to UN stats, while China, India and most of the developing nations are less than 40% urbanised. How many of the 50% of 50% are therefore likely to qualify as “perceptive”? Less than 50% in the West, certainly; perhaps more than 50% in less urbanised countries.
• That leaves less than 10% of the world’s population in a position to recognise climate change from personal observation. And (unfortunately for the debate) most of those 10% are the rural poor of developing nations, the most frequent victims of climate change not the opinion-makers of industrialised nations.

Of course, Hansen’s statistics show that extreme weather events are going to increase very rapidly in number and severity as global warming continues. More and more of us will notice the effects in our daily lives. But that is not really good news.