As French authorities scramble to deal with the fallout of the terrorist attacks in Paris, thousands of organisers and participants for this month's global climate summit in the same city are also racing to be ready.

Among those making last-minute adjustments are likely to be climate scientists at the World Meteorological Organisation, which is expected to announce 2015 as the hottest year on record, even with a full month to run.

The prediction is unlikely to be controversial, with the head of NASA's climate unit Gavin Schmidt this week rating this year a 99.9 per cent certainty to exceed 2014's record heat.

September was itself a standout month for worldwide temperature anomalies. It served as a stark illustration of what happens when a big El Nino event in the Pacific – as we have watched develop since May – combines with the background warming from climate change.

Indeed, the first nine months of 2015 were warm enough for Britain's Met Office to declare the planet was for the first time more than 1 degree hotter than the 1850-1900 average used as a proxy for "pre-industrial times".

While a largely symbolic marker, the Met Office's statement reminded delegates heading to Paris – assuming the event goes ahead amid the security scares – that our planet is halfway to the 2 degree "guard rail" increase nations including Australia agree must be the limit before dangerous climatic changes kick in.

Low-lying island nations in the Pacific and elsewhere say the science suggests a 1.5 degree rise would lift sea levels high enough to inundate them. Among other impacts would be the death or severe reduction of much of the world's coral reefs.

One reason meteorologists were confident that 2015 will be the hottest year was that seven of the first nine months set heat records for land and sea-surface temperatures.

But then along came October. The heat spike last month was so sharp, it will be surprising if reports released on the sidelines of the Paris gathering don't give it prominence.

For one thing, last month was the hottest October in 136 years, the US National Oceanic and Atmospheric Administration announced this week – making it the eighth month of records in 2015.

But it was the size of the anomaly – up 0.98 degrees compared with the 20th century October average – that was most notable. Planet-scale records are hard to break, and advances are typically measured in just 0.01-degree steps. This one was seven times larger.

Australia bakes

Australians will likely feature in science activities at the Paris summit given the country's outsized role in climate research. The country also contributed a fair chunk to the record global heat last month.

Australia's mean temperatures in October were 2.89 degrees above the long-term average (1961-90), the most abnormally hot month in the Bureau of Meteorology's records going back to 1910.

Perhaps because October is a transitional month with bouts of cool and hot spells, many Australians may not have realised how unusually warm it was.

The prolonged heatwave at the start of the month generated the most extreme conditions across southern Australia since a similar event back in 1914. Climatologists comparing the periods have wondered what role that earlier scorcher, coming amid a severe drought, played in prompting farmers to desert their lands and enlist as Diggers in World War I.

Victoria, NSW and South Australia all had Octobers that resembled typical Decembers for heat – an ill portent for a bad summer ahead for bushfires that have already been deadly in Western Australia. (See chart above for the regions of most unusual heat.)

The area of Australia copping highest-on-record maximum temperatures was the largest for any October, covering 54.7 per cent of the country compared with the previous record area of 22.3 per cent in 1988, the bureau said in a special climate statement.Nationally, every day of the month was above average, a first for October.

Victoria's mean maximum temperatures were almost 6 degrees warmer than the October average, eclipsing the previous largest anomaly by any state. That was in September 2013, with South Australia's 5.13-degree anomaly.

El Nino role

The precise role of the big El Nino – one of three strongest on record – in driving global temperatures higher versus the background warming may take years to determine.

The event, in which the Pacific Ocean absorbs less heat from the atmosphere than in a usual year, is yet to peak and may not break up until mid-2016.

What the El Nino's strength implies, though, is that November may well exceed October's abnormal temperatures globally because of the momentum in the system. And if previous El Ninos are any guide, 2016 could yet be warmer than this year. (See NOAA chart above how 2015 compares with other years.)

Just as negotiations to curb emissions are likely to continue well after Paris, so too will the revisions to the temperature record books.