Our media reported that Sydney temperatures “smashed” previous records, marking Sydney’s hottest day “ever”, with bushfire warnings rising to extreme. Temperatures reached 45.8C in Sydney’s western suburbs, Penrith hit 46.5C and Camden 46.1C. The previous record of 45.3C was set on January 14, 1939.

It was certainly hot in Sydney and we do like to know how hot, which is why we have weather reporters. But we should be careful comparing temperature readings from the past. For one thing our technology is different now. In 1939 digital thermometers were not around, whereas they are now, and the old glass thermometers could not easily read tenths.

According to United States Patent 3729998, the inventors of the digital thermometer were Billy Otis Martin, Robert Cherry Martin, Fritz Kurt Mueller and James Parker Chandler, all from Huntsville, Alabama, on April 10, 1970. Digital replaced all glass and mercury in the 1990s when scientists deemed mercury-based thermometers too risky to handle because they had to be swung sharply to be reset.

Neither were gathering stations standardised, and nor are they even so today. In 1939, for all we know, the gathering station on the hottest day of that year could have been atop a building surrounded by reflective roofing iron where some Stevenson screens are still located, whilst current readings are taken at Sydney airport, with exhaust fumes of jets and reflective glass and asphalt greater than in 1939, or on Observation Hill, which is surrounded by a greater and warmer city than existed 74 years ago.

Then there is machine error, and digital thermometer uncertainty ranges from 0.01°C to more than 1°C. Analogue uncertainty is even greater: 1-3°C. So if the error is greater than 1°C even using digital apparatus, then comparing 1939 to 2013 is invalid. It is even worse than that. I tried putting two high quality digital thermometers side by side together in one room in my house. In the space of only ten minutes they both delivered consistently different readings, varying sometimes by over a degree.

Then we discover that many fires had been lit by vandals. A fire in a long deep valley produces smoke and airborne ash that drifts into the air above nearby towns and raises temperatures. Unless exact same fires are lit in exactly the same places as in 1939, with exactly the same winds blowing, we’ll incur more error.

We didn't have to wait long before global warming got the nod. Australian Climate Commissioner Tim Flannery claimed in The Guardian of 11 January that the heat waves in Australia this summer are unprecedented and caused by CO2 emissions. But if a mere 0.5deg increase has occurred over 74 years, is that really “smashing” a record?

Media and mainstream science are eager to prove global warming because it guarantees ongoing funding to study it, and more scaremongering which sells newspapers. But 0.5°C warming over 74 years works out to be a miniscule 0.006°C per year. If this is caused by CO2 emissions, why would three quarters of a century of industrialisation amount to only half a degree rise in air temperatures?

It cannot be global warming because it was also this hot back in 1939 and no one was talking about global warming then. Besides, we know heat on earth comes from the Sun, powered by the Milky Way galaxy around which the solar system spins, the plane of which we bob above and below. These cycles expose Earth and solar system to fluctuations in density and frequency of cosmic radiation.

Add to galactic cycles the earth cycles of eccentricity (our orbit is elliptical), obliquity (we are on a changing lean) and precession (we wobble as we spin). The 100,000-year eccentricity cycle corresponds to the Ice Age-interglacial cycle. Then there’s the 22-year solar magnetic and sunspot cycle, and in the first 10 days of January the Sun is closest to earth for the year, raising the sunspot count.

Then there’s the Moon which approaches closer every month, called perigee. If closest perigees occur in summer (this year’s closest are spanning November to March 2013 with an extreme perigee in December) then summer heat is magnified due to bigger air-tide oscillations.

The monsoon season is late, and a late summer monsoon season delays cooler air descending from north Australia, making heat expand in the interior. When a cold front comes beneath Australia, because heat is drawn to cold, desert heat gets drawn to the southern half of the continent.

So how did 1939 compare to 2013? Just as for 2012/13, the summer months in 1939 had closest perigees for the year. The worst heat-wave in the recorded history of south-eastern Australia occurred in January 1939, two days after an extreme perigee. Between December 1938 to January 1939, 71 people were killed and over 1000 homes destroyed in VIC. Strong northerly winds intensified fires burning in almost every part of the state and ash fell as far away as New Zealand.

Like 2012/13, 1939 was not a year of cyclones in India, there were no cyclones until the end of that January in east Australia and the weak Indian monsoon season correlated with the very hot Australian summer. Six cyclones per year is normal for Australia but in 1939 there were four, none exceeding Category 1, and coupled with a late monsoon. Only the fourth cyclone, between 2-5 March 1939, moved down the eastern seabord bringing monsoon weather southwards.

It has been the same this year, with 2012 among India's weakest recorded monsoon seasons (June to Sept) producing rains 12 percent below normal and causing widespread crop failures. Other deficient Australian monsoon seasons have been 1941, 1951/52, 1965, 1968, 1972, 1974/75 and 1979.
Just for the record their summers all brought extreme bushfires.

Ken Ring of www.predictweather.com is author of the 2013 Weather Almanacs for NZ and Australia.

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