Significance doing the rounds

I'd like to commend to readers a couple of postings on the subject of statistical significance in the temperature records.

Last week a little visited website called Real Climate had an article by climatologist Stefan Rahmstorf, which addressed many of the issues discussed here in recent months. What I found interesting was that there was a measure of agreement:

...the confidence intervals (and claims of statistical significance) do not tell us whether a real warming has taken place, rather they tell us whether the warming that has taken place is outside of what might have happened by chance.

Click to read more ...

Keenan on McKitrick

Doug Keenan has posted a strong critique of Ross McKitrick's recent paper on the duration of the pause at his own website. I am reproducing it here.

McKitrick [2014] performs calculations on series of global surface temperatures, and claims to thereby determine the duration of the current apparent stall in global warming. Herein, the basis for those calculations is considered.

---

Much of McKitrick [2014] deals with a concept known as a “time series”. A time series is any series of measurements taken at regular time intervals. Examples include the following: the maximum temperature in London each day; prices on the New York Stock Exchange at the close of each business day; the total wheat harvest in Canada each year. Another example is the average global temperature each year.

The techniques required to analyze time series are generally different from those required to analyze other types of data. The techniques are usually taught only in specialized statistics courses.

Click to read more ...

A physicist does Bayes

Physicist and science writer Jon Butterworth has written a layman's introduction to Bayes' theorem, touching at one point on its use in climate change:

If you have a prior assumption that modern life is rubbish and technology is intrinsically evil, then you will place a high prior probability on Carbon Dioxide emissions dooming us all. On the other hand, if your prior bias is toward the idea that there is massive plot by huge multinational environmental corporations, academics and hippies to deprive you of the right to drive the kids to school in a humvee, you will place a much lower weight on mounting evidence of anthropogenic climate change. If your prior was roughly neutral, you will by now be pretty convinced that we have a problem with global warming. In any case, anyone paying attention as evidence mounts would eventually converge on the right answer, whatever their prior - though it may come too late to affect the outcome, of course.

The use of Bayes' theorem in climate science is so much more interesting than this: as readers at BH no doubt know, the IPCC's use of a uniform prior in ECS for its "neutral" starting point biased the posterior towards higher estimates of future warming. Secondly, do we really have "mounting evidence"? Surely what we have is comparisons of unvalidated physical models to observations.

Forecast = projection = scenario

Matt Briggs has a post addressing the argument that climatologists are not making forecasts, they are doing projections. This argument, which has always struck me as a master piece of obfuscation, seems not to hold up under scrutiny.

Perhaps afficionados of "projections" can explain why he is wrong.

Lessons from the shop floor

John Shade posted this as a comment on the last post and commenters suggested that it was worthy of standing as a post in its own right. Having read it, I agree that it is well worth discussing.

One of the biggest breakthroughs in industrial statistics occurred in the 1920s when Dr Shewhart of the Bell Laboratories came up with a way to decide when it was likely that a cause of some of the observed variability in a system could be identified. He discovered that engineers and quality control managers, as well as machine operators, who ignored this method were liable to mount wasteful investigations into what they thought were odd or unacceptable data values, and almost inevitably make changes to the production process from which the data came. Such interventions generally made the process worse, i.e. with more variability that it had before. There was a great effort in those days to reduce the noise in telephone connections, and part of this was aimed at reducing the variation from one telephone handset to the next. They dreamed of replacing the old phrase 'as alike as two peas in a pod', with 'as alike as two telephones'. But many well-intentioned efforts were making things worse.

Click to read more ...

Where there is harmony, let us create discord

Updated on Jul 3, 2014 by Bishop Hill

My recent posts touching on statistical significance in the surface temperature records have prompted some interesting responses from upholders of the climate consensus, with the general theme being that Doug Keenan and I don't know what we are talking about.

This is odd, because as far as I can tell, everyone is in complete agreement.

Click to read more ...

The debate at the FST

A report of the recent climate change discussion at the Foundation for Science and Technology has been published here. Audio of the main speakers is available from the FST's website.

Featuring Mark Walport, Jim Skea, Peter Lilley and David Davies, the subject was "What is the right level of response to anthropogenic induced climate change?". From the report of proceedings, little new ground was broken. I was, however, interested to learn from Walport that it is "clear" that climate change is happening and that its impacts are already evident, a position of delicious imprecision: I imagine we are supposed to infer that he means manmade climate change, but of course manmade climate change is not "clear". As I have mentioned previously, I have put it to Walport that we are unable to demonstrate a statistically significant change in surface temperatures because of the difficulty in defining a statistical model that would describe the normal behaviour of surface temperatures, a claim that seems to have the support of the Met Office. I don't know of any other metric in which a statistically significant change has been demonstrated. Walport did not dispute my position on surface temperatures but suggested that seeing many observational metrics moving together led to a conclusion that manmade global warming was upon us.

This may be the case, but I wonder if there is a robust statistical analysis of to support Walport's position. Perhaps a letter is in order.

(Please could we avoid comments that are simply venting about Walport - stick to the issues please.)

Statistical sierra

Sierra Rayne, writing at the American Thinker blog over the weekend, took a gentle pop at AP's Seth Borenstein for making alarmist claims regional temperature trends in the USA while barely paying lipservice to standard statistical techniques.

The AP used "the least squares regression method" to calculate the annual temperature trend for all these regions, but then proceeded to ignore entirely whether the regression method indicated if the trend was statistically significant (the typical criteria would be a p-value<0.05).

This is first-year statistics level stuff.  Quite simply, if your statistical test ("least squares regression method") tells you the trend isn't significant, you cannot claim there is a trend, since the null hypothesis (i.e., no trend) cannot be rejected with any reasonable degree of confidence.

In an area like climate, you would have thought an experienced journalist like Borenstein would take some statistical advice before writing.

LWEC Report Card: A microcosm of global warming exaggeration and errors

This is a guest post by reader 'Peartreefruiting'.

[Addition below by author's request 11.30am, 7.6.2014]

In the Annual Review 2013 of the British Trust for Ornithology there is an article entitled “There will be changes afoot”, which details observed and expected changes to British habitat as a result of global warming.  It contains the statement “warmer springs have also led to a trend towards many biological events becoming earlier”.  Since 2013 was the coldest British spring for 50 years, it seemed strange timing for such a statement, so I decided to probe into it.  The article on its own has no verifiable data, but it gives a link to this page at the LWEC website, which in turn links to a document entitled “Biodiversity English for Web.pdf”.   LWEC is the organization “Living with Environmental Change”, and its website states that it is a partnership of 22 major UK public sector funders and users of environmental research, including the research councils and central government departments.

Click to read more ...

Congratulations DK

Congratulations to eminent hydrologist and occasional (well, once!) BH guest author Demetris Koutsoyiannis, who has been awarded the Dooge Medal for his services to hydrology and climatology.

Also worth reading is the speech Koutsoyiannis gave in response to the award, which describes some of his past and present difficulties in getting his work published:

...my relationship with rejections continues to be fruitful; for example, last year I was able to receive, for a single paper, eight rejections by eight different journals and eventually publish that paper.

The gatekeepers are still busy.

Lewis on radiocarbon

Nic Lewis has a very long and rather technical post up at Climate Audit about the Bronk Ramsey radiocarbon dating algorithm and its statistical problems. It's well worth perservering with though, because when he gets on to testing different statistical approaches to the problem - the Bronk Ramsey subjective Bayesian one, an objective Bayesian one, and a frequentist approach too - the failings of the subjective Bayesian approach become startingly clear.

The different approaches are also considered by means of a rather fascinating analogy, namely the recovery of a satellite that has fallen to Earth.

This is the conclusion of Nic's paper:

Click to read more ...

That was quick

Anthony Watts records the release of a new paper by Shaun Lovejoy of McGill University, which claims to have shown that the chances of recent temperature change being natural are close to zero.

With 99% certainty claimed for the results, all sorts of alarm bells are sounded, and sure enough holes are being picked in the results already: Monckton here and Matt Briggs here.

I think it's fair to say that this particular paper is going to sink without trace.

http://wmbriggs.com/blog/?p=8061

On consistency

In the wake of the Press Gazette "debate", I was watching an exchange of views on Twitter between BH reader Foxgoose and Andrea Sella, a University College London chemist who moves in scientific establishment and official skeptic circles.

Sella was explaining how persuasive he found the observational record of climate:

Think like a scientist! Temperature is only a proxy. Energy balance is real issue & C19 physics is alive and well.

Like Warren Buffett you mustn’t be affected by shorter term fluctuations.

As I said, don’t just look at surface temps. Look at sea level and global ice mass too. All part of same.

Click to read more ...

Walport's presentation

Mark Walport's staff have kindly made available the slides he used in Glasgow. They can be seen here.

As I have suggested previously, the talk was a recitation of the standard case for alarm, but there were many aspects of it that piqued my interest. For example, I noted that while warming up to the first slide he spoke about energy security first, before moving on to climate. Later on in the talk he spoke of the three lenses through which the climate problem had to be viewed and the first of these was again energy security. Is this a new tack? Are backsides starting to be covered? Perhaps.

Click to read more ...

Your environment

Ross McKitrick has unveiled an excellent new initiative:

I am very pleased to announce the launch of yourenvironment.ca, a new project of mine. The idea is very simple: to present the complete environmental record of every community across Canada. The site currently shows air emissions by source (back to 1985), air contaminant levels (back to 1974) and monthly average high temperatures (back to 1900) for hundreds of places across the country. Water pollution data are coming this summer.

The layout is self-explanatory and it's very easy to use. The data are all from government agencies, but most of it has not hitherto been disseminated in a usable form to the public. All my sources are, or will soon be, linked and the data I use will all be easily-downloadable.

So the next time you find yourself in a conversation with someone who (i) is convinced that Canada does nothing to protect the environment, or (ii) thinks winters around here used to be a lot colder/longer/snowier; or it never used to be this warm/cold in April/October/ etc, or (iii) worries/guffaws about the alleged/obvious ecological disaster all around us, and you wonder what, if any, of this is true, look at yourenvironment.ca and find out.

I especially hope households with high school students will learn about it, though from the experience at our home it might put some kids at risk of being expelled.

What an excellent idea. I don't think we have anything like this in the UK.

Any volunteers?