On January 1 Sydney recorded its second highest ever temperature, of 44.2 degrees; the third highest reading, at 44 degrees, was in January 1983, while the hottest was taken on January 14, in 1939, at 45.3 degrees. Readings for the city, taken at Observatory Hill, go back to 1858.

"We've still got a way to break the record. We get a forty-degree day in January about once every ten years. Back in 1960 there were two days over forty, one after the other, so they're not uncommon", says Perry Wiles, the Bureau of Meteorology's Acting Climate Manager for New South Wales.

New South Wales often has such hot dry days in summer, which occur when a high-pressure system lingers in the Tasman Sea, off Australia's east coast, as it did on January 1, for a couple of days. With counter clockwise directional wind around it, the air is then driven over Queensland, and further inland, where it heats up, before moving south into New South Wales, as a very hot dry north- westerly wind. This weather system, that produced the recent heat wave felt across NSW, parts of Queensland, and the ACT, was not uncommon, but the ensuing high temperatures were.

Interestingly, inland Western Australia also had one of its coldest January 1 days on record, being 12 degrees cooler than average, when air moved over a pool of cool water - about one degree below the average ocean temperature) south west of Western Australia � before coming over land.

El Nino/ La Nina events, the Southern Oscillation phenomenon (a major air pressure shift between the Asian and east Pacific regions), climate patterns oscillating on a decadal level, and seasonal variability, all ensure Australia receives extreme and varied weather.

"Our hottest years tend to be El Nino / La Nina years, which occur on a 2-3 cycle, but one of the things that was unusual about last year was that it was so hot, but not an El Nino year", says Wiles.

"One of the things that's fairly convincing for why there's warming is that we seem to be hitting extremes at the hot end more frequently, but we're not getting extremes at the cold end.

"And yet there has been a hotter day, when there's been less C02. So there's a variability - up and down, up and down, up and down - but when you look at that variability over time there's still a trend that's going up, and although you can't say one unusual event is caused by global warming, because you have had hot days before, the fact is the average temperature is gradually going up: by about a degree for Australia over the last century, and the frequency of very hot days is becoming higher, which means there is, on top of the variability, a trend".

There are two factors at work, Wiles continues: "There's the natural variability and a warming trend, and most scientists would say that a significant part of that warming trend is related to human activity".

"You only need a rise of a few degrees in the average temperature to have a very significant impact on ecosystems, which we need to be concerned about. It sounds like a small thing when you compare it to the day-to-day changes, but a one-degree change, long term, does have a big impact."

While a warmer planet means more evaporation, and more cloud, and therefore more rain, the question of where that rain will fall, is of vital importance to the Australian agricultural sector. Wiles says that although rainfall will probably increase, a lot of the Bureau's models are showing that it will fall over higher latitudes than Australia; and there may be more intense events, but less of them, so rain will increase, overall, around the planet, but Australian farmers may not get it where they need it.

Part of the difficulty with modelling, Wiles says, is trying to downscale global models to predict what will happen in a small area, like New South Wales, what the chance will be that rain will fall on location X.

"Projections vary because there's uncertainty related to things like what will happen to CO2 emissions, as well as some of the variables involved, which is sometimes used by climate sceptics to say the whole thing's rubbish, but all the models are pointing to warming of between one and six degrees over the next century on a global basis. On the lower end, that's probably manageable, but at the higher end we'd be in serious trouble - ecosystems would be severely damaged."

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