Understanding Climate Risk

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Time to stop hiding behind warming trends

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Time to stop hiding behind warming trends

By Roger Jones, Victoria University

Dr Rajendra Pachauri, head of the IPCC, has reportedly acknowledged to Graham Lloyd of The Australian, that there is a “17-year pause in global temperature rises”, a fact that apparently has been suppressed in Australia. Dr Pauchauri endorses debate, saying that people had a right to question the science, whatever their motivations.

But according to Lloyd, Pachauri’s views contrast with arguments in Australia that views outside the orthodox position of approved climate scientists should be left unreported.

Am I an “approved” climate scientist? because I don’t hold that view, nor do I know any who does. What we would like, though, is for science to be reported as science and for opinion to be reported as opinion. And for all reporting to be accurate.

Lloyd makes this claim: unlike in Britain, there has been little publicity in Australia given to recent acknowledgement by peak climate-science bodies in Britain and the US of what has been a 17-year pause in global warming. Britain’s Met Office has revised down its forecast for a global temperature rise, predicting no further increase to 2017, which would extend the pause to 21 years.

This is the Met Office’s latest five-year forecast shown below. Skeptical Science reports the Met Office saying: the latest decadal prediction suggests that global temperatures over the next five years are likely to be a little lower than predicted from the previous prediction issued in December 2011. We’re in the midst of a period of La Niñas, which have a slight cooling effect, as do rising sulphate emissions in Asia. But look at the blue line – do my eyes deceive me? Is it level with the previous black line? It’s warmer? Perhaps Lloyd’s computer has a tilt to the right that makes increases look level.

Observed (black, from Hadley Centre, GISS and NCDC) and predicted global average annual surface temperature difference relative to 1971-2000. Retrospective predictions starting from June 1960, 1965, …, 2005 are shown as white curves, with red shading representing their probable range, such that the observations are expected to lie within the shading 90% of the time. The most recent forecast (thick blue curve with thin blue curves showing range) starts from November 2012. All data are rolling annual mean values. The gap between the black and blue curves arises because the last observed value represents the period November 2011 to October 2012 whereas the first forecast period is November 2012 to October 2013. UK Met Office

The Met Office predicts record global mean temperature over the next five years – now that’s news.

News Corporation sells roughly 70% of the newspapers in metropolitan Australia, and its readers are subject to this kind of fudging on a regular basis. It’s no wonder some “approved” scientists are frustrated.

But that’s not the only thing that frustrates me. It is also time to challenge what Lloyd calls the orthodox position of climate science.

Climatology needs to stop hiding behind long-term trends and explain what is in plain sight, and why variations in the rate of warming might be important. I’m working with colleagues at the moment on a National Climate Change Adaptation Research Facility project called Valuing Adaptation to Rapid Change and we’re looking at the economics of rapid change. Non-linear behaviour in climate driving extreme events has the potential to really hurt us.

The first thing to bear in mind is that a trend line is a model. A warming trend is not a theory of how climate changes. If a complex, non-linear system fails to follow a trend, look at the model to see whether it represents the theory sufficiently well.

In a nutshell, the theory says greenhouse gases act like a blanket, trapping heat near the surface. This creates a radiation imbalance at the top of the atmosphere. The earth system warms to return this balance by increasing the heat escaping from the top of the atmosphere so that energy out equals energy in. This is a slow process, taking centuries, because the ocean has to warm sufficiently to support a hotter atmosphere. The scientific confidence in this aspect of climatology is extremely high. A simple trend line is sufficient to measure this process.

But on decadal time scales, the trend-line model fails. Most of the heat trapped in the earth system goes into the oceans. The top 700m of ocean increased in heat content from 3 x 1022 Joules in 1997 to 10 x 1022 Joules in 2010, in a highly non-linear manner, due to mixing rates between the surface and deep ocean. The atmosphere holds as much heat as the top 3m of ocean, about 0.4% of the heat content above. Why on earth then, with highly non-linear processes in the ocean, would we expect a gradual warming trend in the atmosphere?

A paper I published last year shows that most of Australia’s warming occurred in two episodes, one in the late 1960s to early 1970s, when south west WA rainfall also decreased, and the other in 1997-98. The other finding was that most of this warming was anthropogenic. On decadal timescales, step and trend is a much better model for explaining warming than simple trends.

To me, the graph above makes perfect sense: mild trends separated by an instantaneous rise of about 0.3°C. By ignoring non-linearity and projecting future climate change as simple trends, orthodox science is doing us a great disservice. We have not yet woken up to the recent non-linear increases in heatwaves and fire danger in Australia let alone planning for more such changes in the future. The same goes for floods.

Observed and projected percentage area experiencing an exceptionally hot year: Queensland as an example. Note the recent rapid increase (source: K. Braganza, Bureau of Meteorology)

Days above high fire danger, average of 9 Victorian sites, showing statistically significant rapid increase (site data from Bureau of Meteorology)

It’s time to stop defending orthodox science by hiding behind simple trends and come to grips with the fundamental non-linearity of climate change. That’s the risk we need to mitigate, adapting to changes that can’t be avoided.

Roger Jones receives funding from the National Climate Change Adaptation Research Facility. He is affiliated with Climate Scientists Australia and the IPCC.

The Conversation

This article was originally published at The Conversation.
Read the original article.


12 Responses

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  1. When reporting on the statements of Professor Tim Flannery (Chief Climate Commissioner) should these statements be reported as opinion or as science? In fact when is the opinion of a scientist something that should be reported as opinion and when is it something that should be reported as science? It seems to me that your aspiration regarding how things should be reported (this is science, this is opinion) is somewhat unworkable in practice. Or at least trying to enforce it is. Far better to demand that journalists report accurately what people say and that they report the context of those statements fairly and that they be open to criticism if others think they have it wrong. And I think that is in essence where we are at right now anyway.


    March 23, 2013 at 2:04 pm

    • TerjeP,

      it’s quite workable. What we might try to avoid is having journalists who just make stuff up. Like Graeme Lloyd who told readers of The Australian things that were just not true. People get reputations – Flannery does not always interpret scientific findings accurately but Will Steffen who has been called on the clarify them on the odd occasion, does.

      There are a number of newspapers in Australia, owned by one corporation, who continually present things that have been shown not to be true, as matters of scientific debate. And who continually provide soapboxes for those who promote those views. Flannery is right most of the time and newsworthy because he is a person of note. Although he is trained as a scientist – on climate change, he is a scientific communicator, not a climate scientist who communicates. I think people can tell the difference.

      Roger Jones

      March 23, 2013 at 2:16 pm

      • I’m not familiar with the work of Graeme Lloyd. However I agree that journalists shouldn’t just make stuff up. However the way to deal with it when they do is to have other journalists call them out for doing so and to criticise editors that don’t extract a retraction. Of course what is real and what is made up isn’t something people always agree on.

        An example is the recent reports where a journalist stated that Bob Carr was critical of Julia Gillard. Bob Carr said this was untrue. Is the journalist a liar or is Bob Carr? There is really no objective way for most of us to know. Or at least no practical and objective way. However although all of us will form a view of what the truth is.

        Anyway what did Graeme Lloyd say that was untrue?


        March 23, 2013 at 2:28 pm

  2. He said that the UKMO predicted no further increase to 2017, without showing what they did predict. The graph above quite clearly shows predicted warming is much more likely than not.

    Roger Jones

    March 23, 2013 at 2:36 pm

  3. Roger – as an aside I noticed there is an article with your name in it just published by Quadrant. I’m not a reader of Quadrant normally but it refers to a debate between an economist and a newspaper columnist about the temperature benefit of Australia’s carbon tax policy which I’ve tried to follow for a while. The protagonists are John Quiggin and Andrew Bolt and you get dragged in for a special mention.


    Thought you should be aware of it.

    TerjeP (say tay-a)

    March 27, 2013 at 7:23 am

    • Thanks Terje, Will have to get together with John and giggle at this silliness

      Roger Jones

      March 27, 2013 at 8:45 am

      • Does the article cite you correctly in terms of what you calculate we will avoid in the way of warming as a result of Australia adopting a carbon tax of $23 per tonne.

        TerjeP (say tay-a)

        March 27, 2013 at 9:28 am

  4. Terje, I haven’t read it properly and am too busy to do so for a bit (big project report to go in), so will need to consider it carefully later. The devil is in the detail of how the scenarios were calculated. Since John used the same climate modelling assumptions as me differences will be in how the scenario and baseline is constructed. That already suggests the Quadrant kerfuffle likely to be a debate based on assumptions, not science. That is, if John and I calculate the same tonnes of CO2 we will get a similar temperature outcome, if not they will be different.

    For the moment, you can read more here: https://2risk.wordpress.com/2012/07/20/benefits-of-oz-climate-policy-on-the-conversation/

    Roger Jones

    March 27, 2013 at 9:41 am

    • Roger – I understand and fair enough. It’s important to be clear about the start date, the business as usual baseline you are comparing to, the timeframe and the specific policy measure under review. If we are going to compare estimates they need to be apples for apples.

      TerjeP (say tay-a)

      March 27, 2013 at 12:28 pm

  5. […] clearly, that the evolution of climate change is non-linear and not gradual, something I have been banging on about for quite some time. W&C also show that warming is not superimposed on variability in this […]

  6. […] hypothesis is that on decadal timescales climate change is abrupt rather than gradual. Rather than warming on a year-to-year basis, relatively stable periods are punctuated by warming […]

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