Australia's record-breaking heat levels

A study published in the journal Geophysical Research Letters has found that in the past 15 years, new heat records in Australia have outnumbered cold temperature records by 12 to 1 — with global warming said to be the prime cause.

According to lead author Dr Sophie Lewis, from the ARC Centre of Excellence for Climate System Science, “In a climate without global warming the ratio of new heat records to cold records would be 1:1, and that was the case in Australia from 1910–1960.

“But after 1960 the number of heat records increased, while new cold records declined. This trend accelerated again between 2000 and 2014, so that today for every record cold temperature set, 12 heat records are broken in Australia.”

In particular, Dr Lewis and study co-author Dr Andrew King noticed two striking trends in this record-breaking activity:

• Night-time temperatures or minimum heat records were being broken more frequently than daytime temperatures;
• The decrease in cold records being set was most pronounced in the cooler months from April to September than through Australia’s warmer months from October to March.

The findings complement research from around the world showing increasing numbers of global and regional heat records being set.

In examining the changes in record-breaking temperatures, the researchers looked at the influence of El Niño, La Niña and the roughly 24-year cycle of the Interdecadal Pacific Oscillation to see if these natural variations could be responsible.

While these events had some minor impact, the authors claim they did not influence the overall trend of increasing heat records or the global warming signal resulting from human-produced greenhouse gas emissions.

“The only year in the past 15 years to produce more cold records than warm records was 2011, which was impacted by two La Niña events at the beginning and end of the year that brought extensive rainfall,” said Dr King.

“However, the dominance of cold records in 2011 was not caused by an increased number of cold records, which were around average, but by the lack of heat records for that one year.

“By 2012 normal service had resumed, and the trend in record-breaking heat events dominating cold records was back.”

In terms of global average temperatures, the coldest year on record was 1909. Since then, the record for the hottest year has been broken 18 times — and is likely to be broken again in 2015.

“If this trend continues with the continuing rise in greenhouse gases, there may come a time when the chances of a new record cold year being set in Australia will be close to zero,” Dr Lewis said.