Friday, August 13, 2010

Weather vs climate

There is an important and often misunderstood distinction between weather and climate.

Weather is what is happening when you go outside. It is what meteorologists study and consists of dynamical systems that are highly sensitive to initial conditions driven by the movements of blocks of hot and cold air. It is measured hour by hour (or even minute by minute) and predicted a few days in advance, beyond which the complexities and sensitivities of the system make computational estimation almost impossible.

Climate refers to long term patterns of weather. It is what climatologists study and consists of dynamical systems driven by long term fluctuations in solar activity, oceanic currents, surface albedo and atmospheric chemistry (and, over the very long term, by geological forces and plate tectonics). It is measured in decades, centuries and millennia and predicted in decades.

Predicting the climate
Yet this raises a common question: if we can't predict next weekend's weather, how can we predict the climate in 2050? Remember that climate prediction doesn't mean a prediction of weather, on which day it might rain or be a certain temperature at a given location. It means predicting the overall pattern, which, while chaotic from week to week, fluctuates within a certain range over the long term. Climate prediction means predicting changes in that range within which weather might fluctuate.

Imagine a pot of water being brought to the boil. Although predicting exactly where and when a bubble will appear is almost impossible, it is still quite possible (given knowledge of the original temperature and volume of the water and the amount of heat energy being applied) to predict when it boil with some degree of accuracy. Or consider tossing a coin one thousand times. It is almost impossible to know whether any given toss will be heads or tails, but we can all predict that there will be about five hundred of each. Or think of sitting on a packed train. You mightn't be able to guess how the person next to you is likely to vote in an election, but with knowledge of quality polling data (if that is not an oxymoron), you can make a pretty good estimate of the likely distribution of votes on the train as a whole.

So climate and weather are closely related, but it is important to keep their distinction in mind. One way of putting it I heard recently is that climate trains the boxer, the weather throws the punches.

This distinction means that it is not possible to directly attribute any particular example of weather either to anthropogenic climate change or to natural variation. A cold day doesn't disprove the theory any more than a hot day proves it. Each are a tiny piece of evidence in a much, much larger pattern. And when an extreme weather event comes along (such as the current Russian heat wave and Asian floods), this too doesn't by itself prove anything. What does count, however, is the well-recorded pattern of increasing frequency and intensity of such events. Put simply, climate change doesn't cause extreme weather, but it increases the chances of it happening, and increases the extremity of what is possible. This is because warmer air can hold more water, bringing more intense precipitation. By the way, this includes more intense snowfall if the temperature happens to be below freezing, as was seen in the northeastern US earlier in the year. Or as NASA says, this is what global warming looks like.

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Weather vs climate in the media
Given this crucial and often misunderstood distinction between climate and weather, why then would the SMH devote most of the space in an article on climate attribution (and one that is currently "most viewed") to a meteorologist? I'm sure John Fisher is probably a nice guy but he has basically zero qualifications in climate attribution (which is a sub-specialty within climatology). He doesn't even have a PhD in meteorology. It is a little like asking an ambulance driver to offer an attribution of the cause of a cancer. Yes, he's involved in the medical field, but has no relevant qualification in answering the question. He may know some pretty handy first-aid, but he's not even a physician, let alone an oncologist.

On a second reading of the article, I found my answer: " meteorologist [Mr] Josh Fisher" may have no relevant qualifications, but as it says at the bottom of the article: " is a Fairfax Digital company."

This is not uncommon and illustrates an endemic problem with much of the mainstream media. The story is structured around the drama of an implied debate between two experts. This is called he-said/she-said genre that constitutes a quick and easy path to a story for journalists without the time or inclination to dig any deeper and it means that the journalist can claim to be "balanced" since they are giving "both sides" of the story. However, this pretense requires us to assume some equality between both "sides". Yet one "expert" (without relevant qualifications, but who works for a partner company to the journalist's own publication) says it is due to the solar inactivity and another expert (the IPCC, i.e. the peak body on climate and climate attribution whose conclusions are recognised and endorsed by the published stance of almost every major scientific body of national and international standing on the planet) says anthropogenic climate change has loaded the dice to make such events more likely (a little like putting more bullets in the pistol for a round of Russian roulette; not the direct cause of death, but stil...). Faced with these two experts, some artificial ideal of "balance" is not the goal. Honesty and journalistic integrity requires at least a basic assessment of the relevance and reliability of the sources being quoted.

Compare this SMH story to the same issue being covered in the Guardian, which managed to get a real expert to write the piece, the head of climate monitoring and attribution at the UK Met Office, one of the most respected centres of both meteorology and climate in the world.

However, as my next post will argue, even the Guardian continues to make a mistake in how this story has been framed and filed (a fact pointed out in an interesting Guardian opinion piece).


Jonathan said...

Byron, I think you're reading a little bit too much into this. Most of the article is given to Mr Fisher because most of the article isn't about whether it has anything to do with climate change. The business link probably does explain some of the reason for this focus, rather than the arguably more newsworthy focus of the Guardian article, but I don't think it's about providing an artificial "balanced" debate.

I'm a little bit wary of drawing such a big line between meteorology and (especially this sort of) climate attribution, even though I think you have explained weather v climate quite nicely. Surely at worst this is not driver (or even paramedic) v oncologist, but asking your diagnosing oncologist whether your cancer was caused by an environmental factor, where you might get more help from a cancer epidemiologist?

In any case, Mr Fisher doesn't seem to be saying much drastically different from the climate attribuation experts at the US NOAA. They go into the same details of the meteorological phenomenon, and even conclude that "[t]he indications are that the current blocking event is intrinsic to the natural variability of summer climate in this region", while stressing that there is plenty of evidence for an unrelatedly warming planet. I doubt the book is closed on this, but generally the fact that extreme events are made more common by the greenhouse effect doesn't mean that there won't still be extreme events with fairly separate causes, nor that there isn't reason to understand this.

byron smith said...

Jonathan - Thanks for your very thoughtful comment. You're (largely) right. I think I probably overreacted a little to that particular article. I'd just seen too many mainstream articles that simply play off genuine experts against deniers with little or no qualifications (I could cite dozens of examples) and so jumped a little too quickly on this one. For that reason, I've moved the second half of the post below the fold.

I hadn't seen that NOAA page, and it is quite informative. I was basing my comments on the piece by Peter Stott and on a few other articles and comments from climate scientists. As I note, none of them directly attribute the current extreme weather to climate change; they simply make the oft repeated point that ACC makes such events more likely and more severe. The NOAA page is also only discussing the Russian heat wave. The flooding in Pakistan, while also linked to the blocked jet stream, may well have more direct links to global warming as the higher average temperate means a greater capacity of the atmosphere to hold water vapour and so an increase in the intensity of precipitation events.

Even so, with regard to the part of the article that is directly about the possible link between ACC and the current extreme weather events, I stand by my comments about placing Mr Fisher's opinions simply in parallel with the IPCC quotes. I'm also not convinced that your counter-example of the oncologist and the epidemiologist is more illuminating, not least because Mr Fisher doesn't even have a PhD in meteorology. Maybe it might be helpful for comparing the fields of meteorology and climatology more generally, but I suspect that most people know as little about epidemiology as they do about climatology, so its usefulness may be limited.

Jonathan said...

Byron, I know the sort of article you're talking about. I think this article looks worse than it originally was because the last three paragraphs (with IPCC quotes) were simply dumped in from an AFP report, without any integration with the original point. Even the original was not so well written when it comes to the part which mentions climate change, although I did get the impression that Fisher, rather than claiming excessive expertise or even giving a firm answer, was simply saying we don't know much about this. (He refutes the usual denier reference to solar activity, doesn't he?)

As you say, there isn't a real conflict with what Stott says, which focussed mainly on the broad-brush prediction and avoided saying much at all about how this phenomenon fits in. He said that they were working on better understanding the details, and the NOAA CSI team report is part of just that. You're right that my alternative analogy was really about the general comparison of the fields - my point is that climate attribution involves a lot of meteorology and meteorologists (look at the makeup of the NOAA team!) Apart from anything else, whether "such events" are more likely depends on how sensibly you classify events.

It is also true that ACC could be expected to have an effect on the intensity of the resulting precipitation. I don't think the CSI team are even saying that all the factors in the Russian heatwave are unaffected by ACC - just that the most important one was an unusual event which doesn't appear to be linked to global warming.

Anyway, I've rambled enough, but thanks as always, for very thought-provoking discussions.

byron smith said...

Yes, that's a good summary of where things seem to be at. Thanks again for picking me up.

byron smith said...

NYT piece on extreme weather has some good quotes about the links to ACC.

byron smith said...

Good article on attribution from climate central:
"The point is that while it is a perfectly reasonable question to ask: “Was this event due to climate change?” it would more useful to ask a related question: “are we putting ourselves at greater risk of experiencing this kind of event?” And to that scientists can answer with high confidence: yes!

"Now, you might think this question is less interesting or useful, and perhaps not as worth asking than the first one. But we would argue that, in fact, it is very important to pose this question, and to carefully consider its answers.

"Think of smoking, sun bathing without sunscreen, eating lots of junk food and so on. You may not be able – ever – to unequivocally attribute one person’s problem to the effects of these activities: people develop lung cancer without smoking, for example, but as a population we know we are better off wearing sunscreen, watching our cholesterol, and not smoking, since all of these actions have been shown to make the chances of harm to our health lower."

byron smith said...

Another good piece on why we can predict climate on a longer scale than weather.

byron smith said...

Rolling dice on the weather.

byron smith said...

More excellent reporting from Almost every line mentions cold records, until it is acknowledged that September was still 1 degree above the long term average.

byron smith said...

A good analogy for weather vs climate: imagine a swimming pool being slowly filled with water, into which a swimmer dives. The waves caused the swimmer are the weather. The average water level is the climate. From Skeptical Science.

byron smith said...

Two more analogies.

1. Weather is what you dress for; climate is how you buy your wardrobe.

2. "A helpful analogy in this regard is that population averages of human mortality are predictable while life spans of individuals are not."
This second one is from an excellent new official statement from the American Meteorological Society.