Models fail

Professor Ian Chubb, writing in The Australian, responds to Maurice Newman’s recent articles on climate change. But in my view, he fails to make a case for urgent action. The following two sentences encapsulate Chubb’s approach:

I start in a different place and ask a simple question. We have so far pumped two trillion tonnes of a greenhouse gas, CO2, into our atmosphere since the Industrial Revolution, at a rate faster than ever before. Why would we presume that it would have no effect?

If the answer were simple, we would know it. So we have to use the evidence we have to assess the impact now; and we have to use the data to build models to estimate what the impact might be in the future.

Firstly, the reference to “two trillion tonnes” is classic misdirection, of which any magician would be proud, since to the lay reader, it sounds like a truly gargantuan amount – and in absolute terms, it is. However, it isn’t until one realises the entire atmosphere has a mass of five quadrillion tonnes (2,500 times Chubb’s figure), that the sleight of hand is exposed.

But rather embarrassingly for a Chief Scientist, even the figure of two trillion tonnes he cites is wrong. The mass of CO2 in the atmosphere today is approximately 3.16 trillion tonnes (591ppm by mass, 400 ppm by volume). Prior to the Industrial Revolution, CO2 accounted for approximately 290ppm by volume in the atmosphere (equivalent to 428ppm by mass), so pre-industrial mass of CO2 would have been 2.3 trillion tonnes – the difference being about 0.9 trillion tonnes. “We” have “pumped” less than half the amount of CO2 into the atmosphere that Chubb claims.

Furthermore, nobody “presumes that it would have no effect”. We acknowledge that CO2 is a greenhouse gas which will cause some degree of warming. Chubb’s rhetorical question sets up a straw man. The question is not if, but how much?

The models that have been built to estimate the impact of this warming in the future have been shown to be significantly overestimating the contribution of CO2. The IPCC’s blinkered approach has ensured that the majority of natural climate drivers (including the Sun) have been ignored, discounted or dismissed. As a result, the sensitivity of CO2 had to be cranked up (by invoking large positive water vapour feedbacks) to enable to models to match the past. Because CO2 continued to increase, the models predicted continually increasing temperature, but real-world measurements are diverging from model predictions and there is no ‘consensus’ on the reason why (see The Cause has seven excuses for The Pause).

None of this is entirely surprising, given the UN’s scapegoating of CO2 as the culprit at least thirty-odd years ago, and IPCC’s remit to investigate ‘human-caused’ warming.

Similar “why would we presume” arguments are put forward in relation to ocean ‘acidification’ (which he correctly labels as ‘less alkaline’) and ocean heat content. The former is not disputed (although the magnitude of its effects might be), but the latter has been dredged up as one of the convenient excuses for the models failing to match observations (see Rapid increase in ocean heat?).

Chubb quotes a Nature article on models:

“Some have argued, in part on the basis of current temperature trends, that climate models tend to overestimate warming … (but) the evidence cuts both ways.” Some seem always to presume the errors only occur in the direction favourable to their argument. Notwithstanding the range, current models point out a direction, and the direction is up.

Looking at the plot above, can you see the evidence ‘cutting both ways’? How many models have underestimated warming? Since 2005, none. And errors at the IPCC are always in the ‘it’s worse than we thought’ direction – despite the fact that statistically, one would expect a fairly even balance both better and worse.

Chubb concludes:

I am sure Maurice Newman and I would agree that much of what should be a debate has turned into “low-grade” and often personalised argument. What it should be is a healthy and constructive discussion based on all the empirical evidence, not bits of it, and with an eye to the implications for our health, wellbeing and prosperity in the longer term.

With ‘denier’ smear-sites like Skeptical Science, RealClimate and Think Progress still around, I won’t be holding my breath.

Full article here:

Surely CO2 is a climate culprit

AFTER his three recent articles on climate change, most recently on Wednesday, in The Australian, it is clear that Maurice Newman and I can agree on a number of things.

We can now agree, for example, that climate change is real, not a myth or a delusion. We can agree that he is not a climate scientist; and we would agree that I am not one either. We would, I think, agree that a “climate” is the result of complex interactions of multiple variables, many of them natural, but I would say not all.

We diverge when it comes to the impact of greenhouse gases. While we agree that carbon dioxide is a greenhouse gas, Newman wrote of “the myth of anthropological climate change” (The Australian Financial Review, September 13, 2013) and suggested that it is one in a list of popular delusions.

Others will doubtless address some of the details he has raised. I start in a different place and ask a simple question. We have so far pumped two trillion tonnes of a greenhouse gas, CO2, into our atmosphere since the Industrial Revolution, at a rate faster than ever before. Why would we presume that it would have no effect?

If the answer were simple, we would know it. So we have to use the evidence we have to assess the impact now; and we have to use the data to build models to estimate what the impact might be in the future.

Right now we know that as CO2 levels in the atmosphere increase, so too does the amount of CO2 absorbed by the ocean, with the effect of making the water less alkaline (or more acid). Why would we presume that would have no effect on marine life? We also know that the heat content of the oceans has increased consistently although the rise in atmospheric temperature recently is flatter. Why would we presume no effect on the currents, winds and evaporation, and a subsequent impact on climate? We know the planet is warmer than pre-industrial times. While some might dismiss this as just a few tenths (0.9C) of a degree, I wonder if they’d be as sanguine if their core body temperature increased by the same few tenths of a degree.

There will be regional variations. There are differences even within Australia: temperatures in some regions have increased by 2C over 50 years while others have experienced little or no change. Our average change is 0.7C.

We know that greenhouse gases in the atmosphere are important. If there were none, it has been estimated that the global temperature would be around -18C rather than the average near 15C we currently enjoy.

We also know that the relationship between CO2 and temperature is not linear. Uncertainty about the sensitivity of the climate to changing CO2 means models yield different projections. As an editorial in this week’s Nature says: “Some have argued, in part on the basis of current temperature trends, that climate models tend to overestimate warming … (but) the evidence cuts both ways.” Some seem always to presume the errors only occur in the direction favourable to their argument. Notwithstanding the range, current models point out a direction, and the direction is up.

So we know that climate is a complex, complicated matter and that there are multiple variables. Does that mean we don’t use all the information that we have to estimate what might be ahead? Does it mean that we do nothing about one variable over which we have some control – the emission of greenhouse gases? Does it mean that because there are uncertainties, we do nothing?

I am sure Maurice Newman and I would agree that much of what should be a debate has turned into “low-grade” and often personalised argument. What it should be is a healthy and constructive discussion based on all the empirical evidence, not bits of it, and with an eye to the implications for our health, wellbeing and prosperity in the longer term.

Professor Ian Chubb is Australia’s Chief Scientist. (source)