If 2015 is the hottest year since whenever, what will that mean?

There is general acceptance among weather people that we are going to have an el Nino summer in our country. More generally, the el Nino is expected to persist until March/April. This will be good for California and Arizona, which are likely to get heavy rain, and have had drought conditions over the past few years dominated by la Nina conditions, meaning cooler and wetter for us in SE Australia.

Our summer is likely to be hot and dry. Since our dams are pretty full (Sydney’s water storage is at 98 per cent), this is unlikely to be a problem, at least for city-dwellers, unless the el Nino runs into a second year, which it might, though it has been about, in preparation, for much of this year. Lots of people, who should know better, are hoping for an el Nino, because it might signal the end of ‘the pause’ — the lack of significant warming for a decade or much more, according to which dataset you are looking at. Of course, since the el Nino is not connected to carbon dioxide accumulations, the outcome should be seen as yet another example of natural variations which affect temperature, rather than a sign that ‘global warming has started again!’

William Briggs, a fine statistician who writes good things about statistical inference on his website, has pondered on this one too. He starts with a puzzle.

There are two stories floating around about the state of the earth’s atmosphere. Both are believed true by government-funded scientists and the environmentally minded. The situation is curious because the stories don’t mesh. Yet, as I said, both are believed. Worse, neither is true. Story number one is that this year will be the hottest ever. And number two is that the reason it is not hot is because natural variation has masked or stalled man-caused global warming.

Two questions follow, for a reasonable person. How can people believe each of these two ‘divergent contentions’? And why are they false? Briggs answers the first by arguing that climatology has become a branch of politics …. any statement which supports globe warming is likely to be touted by government supporters, even mutually incompatible statements.

Briggs feels that he too is one of the people targeted by the climate scientists suggesting that the RICO Act be used against them. He is properly offended:

In other words, arguments put forward by independent scientists and organisations that do not support the government’s line cannot be considered science, but should instead by classified as criminal acts.

Why will 2015 not be the hottest ever, or on record? Briggs offers some evidence from the geologic record that will be familiar to anyone who has done some reading in this area — for example, this graph.

Yes, it’s a long, long record, and it’s all based on proxies (but then, thermometers provide  proxies too). On the face of it, the earth has generally been warmer than it is now. If you go back only a million or so years, the earth has been in  cold global temperatures (‘ice ages’) for most of that period, much colder than now. Cold is not good for life, which is why we use deep freezes to store food. And the relationship between temperature and carbon dioxide over the long haul is simply equivocal, as the next graph shows.

These graphs are usually dismissed or ignored, on the ground that we are really interested in the contemporary world. Or that there is uncertainty in the data. And there is. But there is uncertainty in all temperature data, wherever they come from. There are two principal sources of uncertainty, measurement error and statistical error, and virtually no one ever points them out on their graphs (these ones too). Briggs  comments: