The poor art of modelling climate change

What was Rob Vertessy, the Bureau of Meteorology’s Acting Head, thinking during his recent chat with ABC Radio Nation’s Fran Kelly about BOM-CSIRO’s State of the Climate Report 2012? He used race-track rhetoric to stress that the Bureau know everything they need to know about what drives climate change, and can make confident predictions. Did he have a flutter while studying for his doctorate in fluvial geomorphology at ANU, or during two decades researching catchment and forest hydrology at BOM?

RN: “Two consecutive La Niña weather events have caused a heat wave in Perth while the rest of the nation had a cool, wet summer. But lower temperatures and record rains do not signal a generally cooler or wetter climate. Global warming continues, according” to your report.

FK: “What is your finding on man-made input into these recent changes (unpredicted downpours) and how much are greenhouse gases contributing?”

RV: “We know (anthropogenic) carbon dioxide is the culprit. It’s a lay-down misere. There’s nothing to debate here.”

A misere is a trick-avoidance bid in card games where a player agrees to win no or a few tricks, usually indicating an extremely poor hand. A lay-down misere is a bid where a player is so sure of losing every trick that the player places his hand face-up on the table. In Australian gambling slang this might be referred to as a ‘dead cert’.

Yet there are some big questions that are not a ‘dead cert’. Where are the established laws of climate change? Will stabilising atmospheric CO2 concentration at 450 parts per million really limit global temperature increases to 2C? What evidence supports the ex cathedra claims of government agencies, such as “there is nothing to debate here” and “climate change is continuing…multiple lines of evidence show that global warming continues and that human activities are mainly responsible”.

Are they putting the confirmation bias cart before the scientific horse?

That the planet’s climate is changing is hardly news. Perhaps what punters need is a form guide on the climate’s causal linkages and the hard evidence supporting them?

In a speech at a U.K. House of Commons seminar last month, distinguished U.S. atmospheric physicist Richard Lindzen summarised the current state of knowledge:

“I will simply try to clarify what the debate over climate change is really about. It most certainly is not about whether climate is changing: it always is. It is not about whether CO2 is increasing: it clearly is. It is not about whether the increase in CO2, by itself, will lead to some warming: it should. The debate is simply over the matter of how much warming the increase in CO2 can lead to, and the connection of such warming to the innumerable claimed catastrophes. The evidence is that the increase in CO2 will lead to very little warming, and that the connection of this minimal warming (or even significant warming) to the purported catastrophes is also minimal. The arguments on which the catastrophic claims are made are extremely weak and commonly acknowledged as such. They are sometimes overtly dishonest.”

The jury seems to be still out on crucial aspects of climate attribution (causation), especially at the regional level, despite emphatic claims about settled and consensus science from the decarbonising crowd.

Another BOM-CSIRO partnership, the Centre for Australian Weather and Climate Research, admitted as much in its 2011 Technical Report 036: “the degree to which global warming may have enhanced heavy rainfall in some parts of eastern Australia remains uncertain”. The much promoted “current generation of climate models” gave “no clear guidance” as to whether the El Nino-Southern Oscillation (ENSO), one of the most important drivers of the continent’s weather and climate, “will change in response to global warming. Some models have strengthened ENSOs, some weaker, and others exhibit little if any change”.

A Swiss modeller has advised that while he is confident the currently non-existent forecasting ability of climate general circulation models (GCMs) “will improve” over time, it will “do so more slowly than some people are hoping”. It could “easily take another 20 years or more to get close to that goal”. Yes, another two decades or more to “predict” future mean climatological states (MCSs).

As for the ENSO frequency, “it’s an initial condition problem much like the weather forecast. There are inherent limits of predictability on those timescales.” So why are we being served this dish that Australia’s future MCSs, and ENSOs, are already predictable?

Little wonder punters are confused, when some agencies seem determined to give them the impression that the determinants of global atmospheric circulation are known with high certainty; while other groups construct tricky each-way-bets and promote them as genuine “predictions”, in a manner reminiscent of the medieval astrologer. When they get it wrong, too much “natural variability” is a favourite default position and all-too- convenient culprit.

Fortunately, no one will be around to do an audit on this “on-the-other-hand, could, perhaps, more-likely-than-not” ninety-year gem from the BOM-CSIRO report (page 5):

“On the other hand, it is more likely than not that heavy rainfall events will also become more frequent across much of Australia. This means that when long dry periods are interrupted by welcome periods of wet weather, the rain is more likely to fall as heavy downpours than as extended drizzle. For southern Australia, a heavy rainfall event that currently occurs once every 20 years could become more frequent by mid-century, perhapsoccurring once every 15 years, and more frequent again by the end of the 21^st century – about once in every 10 to 15 years.”

Consider this one too: “Climate models suggest long-term drying over southern areas during winter and over southern and eastern areas during spring. This will be superimposed on large natural variability; so wet years are likely to become less frequent and dry years more frequent. Droughts are expected to become more frequent in southern Australia; however, periods of heavy rainfall are still likely to occur.”

BOM-CSIRO concluded “an increase in the number of dry days” is expected for Australia, “but it is also likely that rainfall will be heavier during wet periods.” So if it’s wet, they will be right and if it’s dry they will be right too. But can they tell the punters what they really want to know, precisely when, where and why it will be wet or dry?

Whatever happenstoday, the alleged cause is not witches or their familiar but a modern demon, “climate change” - code for anthropogenic global warming; code for “dangerous” levels of carbon dioxide; code for developing world “climate reparations” and the U.N. recasting itself as an Orwellian global carbon cop, and so on. Climate change seems to be driving virtually everything – real and imagined - from the behaviour of clown fish to the proliferation of an international class of alarmist social scientists, economists, politicians and anxious citizens.

As H.L. Menchen observed last century: “The whole aim of practical politics is to keep the populace alarmed (and hence clamorous to be led to safety) by menacing it with an endless series of hobgoblins, all of them imaginary.” Climate change, and carbonorexia nervosa, is the bighobgoblin for our times.

No surprise, then, that scepticism is growing. After all, how persuasive are agency predictions (aka “projections”) that are so distant, ambiguous or absurd they are essentially meaningless?

Punters are being asked, or told, to accept that, on a planet where daily temperatures vary around a -40C to +40C range and where dataset quality and coverage over time and space varies from less than ideal to inadequate, it is possible to detect a decadal “anomaly” of around two tenths of a degree Centigrade and determine a meaningful “average” global temperature, and so on.

BOM researchers used to be more cautious about the black art of prediction, unlike their apocalyptical colleagues over at the Canberra Carbon Cargo Cult Club. Probability outlooks, they warned punters not so long ago, should not be used as if they were ‘categorical forecasts’. They were merely “statements of chance or risk. For example, if you were told there was a 50:50 chance of a horse winning a race but it ran second, the original assessment of a 50:50 chance could still have been correct.”  Heads we win. Tails you lose.