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Thursday, February 2, 2017

Brisbane and Sydney turn on record heat in January 2017 with record warm nights

Averaged across the state, Queensland had its 6th warmest January on record. Mean minimum temperatures were the second-warmest on record for January. (see above deciles average map for January)

But the City of Brisbane in the south east just experienced it's warmist January on record. Back to back heatwaves have brought persistent heat to south east Australia, and especially to southern Queensland and New South Wales. The town of Moree has had 36 consecutive days of temperatures over 35C, doubling the previous record of 17 days in 1982.

Daytime temperatures were described as well above average, but with overnight temperatures record warm in Brisbane.

Rainfall was also well above average in the Brisbane city area, and in western suburbs for January.

Very warm days; record warm nights in Brisbane

Brisbane, Brisbane Aero and Logan City had their highest January mean temperature on record.
Brisbane mean temperature reached 27.2 surpassing the old record of 27.0 set in 2004.
At Logan City Water Treatment Plant mean temperature reached 26.8 surpassing the old record of 26.5 set in 2004.
Brisbane Aero also set a new mean temperature record of 26.3 surpassing 26.2 set in 2013.
Archerfield Airport mean temperature reached 27.1, but fell short of the record of 27.7 set in 1994.

Warmest monthly mean minimum temperature on record, for any month.

Overnight temperatures were also well above average for January in Brisbane. New record high mean daily minimum temperature records were set.

Brisbane Tmin reached 23.0 surpassing 22.8 set in 1973.
Logan City Water Treatment Plant Tmin reached 22.3 surpassing 22.0 set in 2013.
Brisbane Aero Tmin reached 22.8 surpassing 22.7 set in 2013.

Archerfield Airport went down to 22.2 just 0.2 degrees short of the 22.4 record set in 1994.

The Record highest January daily minimum temperature was achieved on 21 January. The new record high daily minimum in Brisbane was 28.0 equalling the minimum temperature on the 29th in 1940. Brisbane Aero record minimum was set with 27.3 surpassing 26.4 set on the 26th in 1998.

Long term trends

The Maximum summer temperature trend, shown at Brisbane airport, is only 0.05C increase per decade.

Mean summer temperatures are rising slightly faster than maximum temperatures at 0.11C per dacade.

It is minimum summer temperatures that are rising the fastest at 0.17C per decade, three times as fast as maximum temperatures. Welcome to the new normal of more frequent and hotter nights.

Amberley, further west of Brisbane shows a long term trend of 0.06C per decade for Summer maximum temperature, 0.13C per decade for Summer mean temperature, and 0.2C per decade for Summer minimum temperature.

Brisbane's temperature future

Okay, so what is going to happen in the future.

Research at the University of Hawai by Camillo Mora and colleagues gives us an idea. They modelled temperatures trend for a global grid using the emissions pathway scenarios of RCP 4.5 (Moderate emission reduction) and RCP 8.5 (Business as usual which is the path we are currently following).

They mapped the climate departure of major cities, putting a year date when we are likely to exceed our current climate variability envelope, when the average cold day is hotter than the average hot day. Displayed below are the data from one out of the 39 models used: the Institut Pierre Simon Laplace Earth System Model CM5A-MR (under RCP4.5 and RCP8.5) for the data point located near Sunshine Coast, just north of Brisbane.

The authors, using 39 climate models, determined Brisbane is likely to pass it's climate departure point around 2042 if we don't do anything and by 2070 if we moderately reduce our emissions.

Sydney turns on the heat

The average maximum temperature in Sydney was 29.6C exceeding Brisbane’s average maximum of 27.2C. That provided a new record for Sydney beating the previous mark recorded in 1896 of 29.5C by 0.1C.

Sydney had 11 days in January when the temperature exceeded 30C and five days above 35C, smashing not only all previous records for the month but for any month since records began in 1858.

Here is how the Bureau of Meteorology summed up Sydney hot January temperatures.

  • Daytime temperatures were well above average across Sydney during January, with several stations, including Observatory Hill, recording their warmest January on record
  • At Observatory Hill, the January mean temperature of 25.6 °C was the highest on record for any month
  • Minimum temperatures were also record warm across the city, with all Sydney stations recording their warmest January mean temperature on record
  • At Observatory Hill, eleven days reached 30 °C (average 3 days) and five days reached 35 °C (average 1 day), in both cases the second-highest number on record behind January 1896
  • Only three days failed to reach 25 °C, the equal-fewest on record with January 1994 (average 13 days)
  • In western Sydney, Richmond recorded seven days above 40 °C and Parramatta recorded five days above 40 °C, breaking the records set in January 2003
  • Five nights remained above 24 °C, more than double the previous record of 2 hot nights in 2010, with 25 nights remaining above 20 °C, the highest number on record (average 9 nights)
  • Several stations recorded their warmest January night on record on either the 14th, 18th, or 31st
  • Temperatures were particularly warm at Observatory Hill on the morning of the 18th, with record-warm temperatures of 31.2 °C at 6am and 36.5 °C at 9am

The long term average temperatures (1910-2016) for Sydney (observatory Hill) show a minimum temperature rise of 0.14C per decade. The mean temperature rise was 0.15C per decade and the maximum trend was 0.16C per decade. But further west where the sea breezes don't reach to moderate summer heat and the urban heat island effect, there is a marked difference.

The weather station at Richmond shows summer max temperatures rising at 0.03C temperature rise per decade. The minimum temperature rise is 0.27C per decade, almost double the rate at Observatory Hill some 49 kilometres away. Over the last 77 years there has been a 2C warming in average minimum temperatures at Richmond.

You can read a report by Peter Hannam at the Sydney Morning Herald: Sydney weather: City marks hottest month ever with every site setting records.

I reported in July 2013 on the impact of climate change and urbanization on temperatures in Sydney:

The study - Temperature response to future urbanization and climate change (abstract) - highlights the combined impact of both new urbanization and climate change on near-surface temperatures for greater Sydney, with positive feedbacks between urban expansion and global warming at the local scales. While Maximum daytime temperatures (Tmax) for Sydney are projected to only increase slightly and mostly in the winter, most of the change will be seen in substantial increases in nigt-time temperatures (Tmin), particularly in Spring and Summer months.

The Urban Heat Island effect is more pronounced at night time which helps in increasing minimum temperature trend. The urban heat island (UHI) as primarily a night-time phenomenon has been well known since 1982. During night time there is a different structure of the atmospheric boundary layer with less turbulent mixing preventing radiation of excess heat stored in urban surfaces during the day. Night time is also when evapo-transpiration is close to zero over both urban and rural surfaces, preventing cooling. During heatwaves wind is also likely to be reduced at night so that there is less advective cooling available to reduce temperatures. (See my Climate change and heatwaves in Melbourne - a Review)

Bureau of Meteorology climatologist Agata Imielska told the Guardian, “One factor is the ongoing warming trend – we’ve warmed by a degree in the past century and it’s not just about averages, we see increases in these extreme temperatures as well,” Imielska said.

“It doesn’t just go for land temperatures, it also goes for ocean temperatures. In 2016 we saw the warmest ocean temperatures on record.”

“We’ve also had warm offshore sea surface temperatures – that also keeps conditions warmer, particularly at night,” Imielska said. “As a result we have seen that back-to-back heat and the lack of relief – the surprising thing is that there haven’t been any really cool days.”

Moree swelters through 36 consecutive days over 35C

Regional NSW has also sweltered through January. There were few daily temperature records were set, but many locations across the state in the north and east broke records for the number of hot days or warm nights. Records were set for the persistence of warm conditions, with extreme heat extending from December and continuing into February.

In Moree they have set a new heat persistence record for the number of hot days over 35C. Temperatures reached 35 °C at Moree for 36 consecutive days between 27 December and 31 January, more than double the record spell of 17 hot days set at Moree between 28 December 1981 and 13 January 1982.

In Moree too, it's the warmer nights that should concern people more. The rise in average summer maximum temperatures is only 0.2C per decade, but average Summer minimum temperatures are rising at 0.22C per decade.

It's only going to get hotter and more persistent with climate change.

The last three years - 2014, 2015 and 2016 have each been the hottest years on record in succession.

But if we look to Canberra and our Federal politicians we still see a morass of climate inaction with elements of climate denial from the Federal Coalition parties. We are far from reducing emissions at the rate necessary to meet our international commitments. The Prime Minister and environment minister are even attacking renewables, instead of planning for transition of the electricity grid to ensure security and redundancy of supply with higher levels of renewables in the mix.


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