One of the difficult things for us non-expert lay observers of the ongoing global warming debate is that the zealots on both sides seem to have little hesitation in misusing climate statistics to “prove” their case. The website of global warming sceptic John Daly currently contains a particularly egregious example, and it highlights my hometown Darwin. Daly says:
Darwin, the capital city of the Northern Territory and deep in the tropics, normally has daytime temperatures around 32 to 33 °C all year round, with overnight temperatures typically in the low to mid 20s celsius.
But not this August or September. There were some of the coldest temperatures in decades during August and finally on 5th September, Darwin recorded the lowest September temperature since records began, 15.1 °C., a real cold snap for a tropical location like Darwin. The previous lowest temperature was 16.7 °C on the 9th of September 1963.
The local media was informed of the new record and it will be available here. The records are also published in the NT Monthly Weather Review. However, had Darwin recorded a hot temperature record, it would have been proclaimed loudly from the rooftops of all the major media, announcing the coming of the greenhouse Armageddon.
But for a cold record? Only the local media takes interest or needs to know.
However, the facts bear very little relationship to Daly’s claims.
It’s certainly true that 5 September (last Friday) was the coldest September night on record at 15.1 °C, and the couple of nights before that were fairly cool too. However, it’s been warmer and steamier ever since, and has actually rained most days, hinting at a possible early beginning to the build-up. I even got soaked by a tropical downpour early this morning while on my daily bike ride along Casuarina Beach. Moreover, and directly contrary to Daly’s claim, the month of August wasn’t especially cool. In fact this map from Darwin Bureau of Meterology for the month of August shows that temperatures were slightly above the long-term average throughout most of the NT including Darwin itself. As any Darwinian will tell you, the dry season just ending has been a fairly disappointing one: neither as cool nor as dry as one might have hoped (although quite pleasant nonetheless). Maybe we’ve just been spoiled by the superb dry season Darwin experienced last year, which actually was the coolest on record.
Incidentally, Daly’s claim that “overnight temperatures 1 typically in the low to mid 20s celsius” in Darwin is also misleading. It’s certainly true for the year as a whole, but dry season night-time minimum temperatures are typically between 18 and 22 °C, so while 15.1 °C is certainly cool it isn’t as great a contrast as Daly’s treatment suggests.
Finally, it’s worth noting that isolated temperature minima or maxima (or even a run of high or low temperatures) prove nothing at all about global climate change. Local weather patterns are highly variable, and only long-term changes in averages have any significance. This is even more true for somewhere like Darwin, where temperatures and rainfall are heavily affected by extremely variable large-scale weather events, namely the incidence and tracks of tropical cyclones and the arrival date and intensity of the north-west monsoon each year. Moreover, most of the computer climate models on which the global warming advocates rely project very little long-term warming in the tropics. They actually show most of the warming taking place in higher latitudes, mostly in winter and mostly at night. Thus you wouldn’t really expect to see a place like Darwin becoming measurably hotter (or colder) even if the alarmists’ worst-case warming scenarios turn out to be true. So Daly’s story is a classic beatup of the worst sort.
On the other side of the global warming debate, the blogosphere’s own John Quiggin has also been enthusiastically misusing statistics in the opposite direction to Daly. Professor Q says:
Anyway, I was particularly interested in Australian contrarian John Daly because, earlier this year, he took the unusual step of making a testable prediction. In this entry he predicted that, with the sunspot cycle turning down and El Nino ending, the climatic extremes of 1998-2002 would be a thing of the past.
Finally, last year in 2002, even before the solar cycle had started its usual decline towards the cooler Solar Minimum, we saw the development of another El Ni±o on top of an already stretched out solar maximum. A Solar Maximum happening concurrently with an El Ni±o, with no cooling volcanic action for the last 10 years, is a potent combination climatically. And the weather has been very active as a direct result of this combination.
But it will pass. These things always do. The solar cycle is now heading down towards its expected solar minimum around 2006, while the current El Ni±o is expected to wane in the next few months, possibly being replaced by its cooling counterpart, La Ni±a.
The greenhouse industry has thrived off Nature’s climatic drama of the last 4 years, using a combination of public hysteria and bent statistics, but the pickings will be leaner in the months and years ahead – until we reach the next El Ni±o or the next solar maximum expected around 2012 (the same year the Kyoto Protocol expires) .
How has this prediction stood up so far? As Daly’s own site shows, the solar cycle has indeed turned down, and the El Nino has passed, (though without a return to La Nina). But, in case you haven’t been reading the news, the weather hasn’t got any cooler.
Professor Q then claims that Daly has been proven wrong but is refusing to admit it. To make good his claim, Professor Q links to this page at the NOAA/National Climatic Data Center graphing global surface temperatures for the month of July 2003. The accompanying commentary observes that “For July 2003, the global average land and ocean surface temperature was 0.53 °C (0.95 °F) above the 1880-2002 average, ranking as the second warmest July in the period of record” and “For January-July 2003, the global average land and ocean surface temperature was 0.54 °C (0.97 °F) above the long term mean, third warmest”. From these graphs and comments Professor Q purports to conclude that “the weather hasn’t got any cooler”. But the NOAA figures don’t support that claim at all, nor do those of the Goddard International Space Center (on which I suspect the NOAA figures are based). GISS statistics in fact show that the global average temperature for the period December 2002-May 2003 was 0.15 °C cooler than the corresponding period the previous year, the temperature for June 2003 was 0.05 °C lower than June 2002 and that for July 2003 was 0.09 °C lower than July last year. Thus the weather has got cooler since last year, albeit only slightly so far. But that’s pretty much what you’d expect (whether or not Daly is correct). The recent El Ni±o only started to taper off around February, so you’d expect that temperatures would so far only have fallen slightly. It’s simply too early to tell at present, and Professor Q does his credibility no good at all by leaping on the July figures (which were significantly affected by a 2 week heatwave across most of Europe during late July and early August) and claiming for them a significance they simply don’t have. The proof of Daly’s pudding will lie in what happens between now and 2006. If the global average temperature falls back to well below the long-term average by 2006 that would suggest Daly may be correct. On the other hand, if it continues to fall but remains above the long-term average, that will clearly demonstrate the imprint of man-made global warming.