2013 will go down as the year that registered Australia's hottest day, month, season, 12-month period - and, by December 31, the hottest calendar year.

Weather geeks have watched records tumble. These tallies include obscure ones, such as the latest autumn day above 45C (Western Australia's Onslow Airport at 45.6C on March 21), the hottest winter's day nationally (29.92C , August 31), and even Wednesday this week, with the hottest-ever 9am reading (44.6C, at Eyre weather station near the WA-South Australian border).

''We're smashing the records,'' says Professor Andy Pitman, director of the ARC Centre of Excellence for Climate System Science at the University of NSW.

''We're not tinkering away at them - they're being absolutely blitzed.''

Global interest in Australia's extraordinary year of heat flared early on. In January, when models started predicting heat that was literally off the charts, the Bureau of Meteorology added new colours to the heat maps - deep purple and pink - to accommodate maximum temperatures of 50-54 degrees. Moomba fell a shade short, reaching 49.6C on January 12.

But for Dr David Jones, head of climate analysis at the bureau, the year's stand-out event was a whole month largely overlooked by a media diverted by the football finals and federal elections. ''From a climate point of view, what happened in September was probably the most remarkable,'' he says.

September's mean temperature soared to be 2.75 degrees above the 1961-90 average, eclipsing the previous record monthly deviation set in April 2005 by 0.09 degrees. Maximums were a stark 3.41 degrees over the norm, with South Australia's top raised by 5.39 degrees and NSW's by 4.68.

The heat swept away the previous September mean record by 1.1 degrees.

''To have 103-104 years of observations, you don't expect to break the record for a continent for a month by a degree,'' Jones says. ''We're very fortunate we haven't had a month that anomalous in the middle of summer.''

Summer heat

Summer was a scorcher. Sydney clocked its hottest day in records going back to 1859, with the mercury peaking at 45.8C on January 18. Hobart notched up 41.8C on January 4, its hottest in 120 years of data.

January baked, becoming Australia's hottest single month in the hottest-ever summer. The duration and area affected by the heatwaves - rather than heat spikes - came to characterise much of the year of exceptional conditions.

''January was incredibly hot for such a long time for such a large area,'' Jones says. ''In many ways we were very fortunate not to have had a frontal system like Black Saturday [in 2009] to draw down that hot air into a coastal zone with a gale-force wind.''

Fires destroyed hundreds of properties in Tasmania in January, and a similar number in NSW in October. The latter came after a remarkably warm and dry stretch, in which Sydney marked its hottest July and September, and second-warmest August and October.

Sydney's record year

''August was the first month in 2013 to see year-to-date records for Sydney,'' says Dr Aaron Coutts-Smith, head of climate monitoring in NSW for the bureau. ''September onwards pushed us ahead.''

Sydney's year will break the city's record for maximum and probably also mean temperatures, Coutts-Smith says. The former was running at 23.6C before Friday's blast of summer heat - well ahead of the previous high of 23.3C set in 2004.

The harbour city's average maximum is about 1.9C above the long-term norm - enough to match a typical year in Byron Bay, about 800 kilometres up the coast.

Australians might want to get out a map to consider conditions further north than where they live. Hot years are now about two to three degrees warmer than cool ones 100 years ago.

''It's a very large change,'' Jones says. ''That's the equivalent of moving in the order of 300-400 kilometres closer to the equator.''

Nowhere below average

For Australia, the year to beat for heat was 2005, when national mean temperatures were 1.03 degrees above the long-term average. As at the end of November, the country was tracking 1.25 degrees above the norm, with a hotter-than-usual December expected.

''As best as we can tell, not a single part of Australia has seen below-average temperatures for this year,'' Jones says, noting that Australia's land-ocean region hasn't had a cooler-than-average year for almost two decades.

Global temperatures are rising too. Last month was the hottest November in records going back to the 1880s, the US government reported this week. That put 2013 on track to be the fourth-hottest on record - behind 2010, in first place, and 2005 and 1998, roughly equal second.

Jones dismisses claims regularly aired by climate sceptics that the planet stopped warming in 1998.

''Certainly there is no global surface data set which shows 1998 was the warmest on record.'' Globally, the climate system holds significant heating momentum as humans continue to burn fossil fuels and drive the emission of other greenhouse gases.

Carbon dioxide levels rose 2.2 parts per million to 393.1 in 2012, bringing atmospheric levels to 41 per cent higher than in pre-industrial times, the World Meteorological Organisation said last month.

''If you actually look at the amount of heat that the earth's absorbing, it's tracking up almost monotonically,'' Jones says.

Wake-up call

Pitman says 2013's likely global ranking of fourth-hottest year ever is exceptional not least because the most significant driver of climate variation - the El Nino-Southern Oscillation in the Pacific - remains in neutral mode. He likens this to the surprise when an athlete at sea-level breaks a record that had been set at high altitude.

''We shouldn't be breaking records in any years other than an intense El Nino,'' he says. ''Quite why the globe is as warm as it appears to be is worrisome.''

By extension, the next El Nino - in which the central and eastern Pacific Ocean usually warms up and eastern Australia gets drier conditions - has the potential to exceed this year's record-breaking Australian heat.

''If we get that additional anomaly, it might even be enough to trigger an awakening in the eyes of some of our leaders,'' Pitman says.