Extreme weather – Townsville

Weather is not climate (climate is what you expect, while weather is what you get) but bizarre weather can be a sign of a changing climate. In fact, Hansen showed a while ago (see my discussion here) that if the climate is warming, which no reasonable person seriously doubts any more, then we will get more extreme weather events – and you can read ‘more extreme weather events’ two ways, because they will individually be more extreme and there will also be more of them.

This is being borne out very close to home for me. I noted recently that Townsville had had the coldest May day in 22 years. Early this week we had the wettest July day in more than 70 years. The Townsville Bulletin reported that …

More than six times the total average July rainfall was dumped across Townsville in just 24 hours with an average of 89mm clocked from 9am Monday [July 9] to 9am [Tuesday]. More than 40 regions from Bowen to Cairns were drenched with over 100mm of rain …

Daily rainfall records were set along the northern coastline … With 145mm, Innisfail recorded their wettest July day in 125 years while Lucinda totalled 141mm, making it their heaviest rain in 118 years. Burdekin residents also saw record-breaking falls with Home Hill’s wettest July day in 87 years and Ayr’s heaviest falls in 59 years.

Just a little less locally, cane farmers fear another wet winter will reduce their yield and delay their harvest. But wet winters are part of the longer-term climate change on which our extreme weather is superimposed.

The BoM publishes interactive Climate Trend Maps and playing with them is simultaneously kind of fun, instructive and perturbing. Here are some maps to to think about, if you haven’t time to play:

  • Queensland annual rainfall, diminishing rapidly along the coast except up around Cooktown – but the *winter* rainfall is actually increasing, although not as much as the annual total is decreasing. Spring rain is not changing much, so the decreased annual rainfall is actually a large decrease in Summer-Autumn (our Wet), partially compensated by a small increase in Spring (on the North coast) and Winter.
  • At the same time our maximum temperatures are trending higher in all seasons (click here and toggle through the seasons).
  • So are sea surface temperatures, which is one reason coral reef scientists despair about the future of the Great Barrier Reef – e.g. the Statement from the 12th International Coral Reef Symposium in Cairns, 9-13 July 2012.

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.

Climate change and extreme weather events

For the last few years I, among others, have been looking at the news and wondering to what extent this, that or the other extreme weather event – the 2010 Russian heatwave, the Queensland floods, record flooding in Thailand, etc – was due to climate change. When I asked those who ought to know, the response was always, “There is probably some influence there but it is too hard to disentangle from natural variation, so you can’t just say that it was caused by global warming,” or words to that effect.

This week RealClimate reported on a scientific paper by Stefan Rahmstorf and Dim Coucou which puts statistically verifiable numbers on the feeling that, yes, global warming is making our weather more extreme. RealClimate’s report is a (relatively) non-technical introduction to the findings and it is linked to the paper itself if you want more.

My really short, really non-technical summary is that the number of record-breaking events increases in proportion to the rate at which the normal (average) conditions are changing. That matches my gut feeling very well, which naturally pleases me. But it simultaneously alarms me because it means that record-breaking events are going to get more and more frequent unless we can quickly and radically reduce our CO2 emissions.

Back to the science: the authors applied their technique to the Russian heatwave and found, “an approximate 80% probability that the 2010 July heat record would not have occurred without climate warming.” That quote is from  the abstract of the paper, meaning that it is in careful scientific language, i.e. there is an approximate 99.9% probability that they can back up every word of it.

The Comments on RealClimate posts are usually well worth reading. Two caught my eye this time:

(1) Comment 36: Ricky Rood looks at other ways in which the 2010 Russian heat wave was extreme:

The winter of 2010 and the spring of 2011 were characterized by very high food prices. An essay by Sarah Johnstone and Jeffrey Mazo entitled, Global Warming and Arab Spring, draws a convincing line that the pressure on food prices was a contributor to the start of the revolutions of the Arab Spring – the tumultuous uprising against many Arab governments. (also here) To diffuse the arguments that are sure to follow – this was a contributor, along with many other factors that came together to fuel a movement. This is the idea of climate extremes as a threat multiplier.

(2) Pete Dunkelberg says:

For a first approximation, an outlier [i.e. extreme event] in the direction of a trend tells you what’s coming. … Just from the shape of a bell curve (and this is far from original) one can see that you don’t have to move the mean very far in one direction for outliers on that side to become much more frequent. A one hundred year heat wave or flood readily becomes a ten or five year event. The new hundred year flood is going to drown people.

Now, how did that Chinese curse go? “May you live in interesting times” – was that it?