May, and autumn, will come close to setting warmth records for Sydney, the state and the rest of Australia as the giant El Nino added a hot overlay to temperatures that are rising in the background here and in most parts of the world. While a flurry of recent cold fronts may finally have ended the Harbour City’s run of balmy days, there are more than enough weird weather numbers and charts to keep weather nerds happy.
Earlier this year, Sydney had a record 43 days in a row with maximums above average, in the period up to March 18.
That record stands but 2016 now also counts the equal-second longest such run, with 33 above-average days up until Thursday.
The latest sequence – broken by Friday’s top of a sub-par 18.6 degree – matched the 33 days of warmer-than-average weather to June 5, 2014, Acacia Pepler, a climatologist at the bureau, says.
With Thursday nudging past 20 degrees, the city had 141 such days in a row after a rare cool patch in early January. The record of 180 such days stretched from November 6, 1913 to May 4, 1914.
Even with a cool final week in the month, Sydney may yet set a record for average daytime temperatures, with 23.2 degrees set in 2014 the mark to beat. As of May 26, the month-to-date average was 23.8 degrees – but with a few chilly days to go, the tally may fall just short.
Sydney may also come close to its warmest autumn on record. The mark to beat was set in 2014 when mean temperatures – the average of day and night – came in at 20.2 degrees, just ahead of 1958, according to the bureau. Maximums for the 2014 autumn were also a record 24.5 degrees, while so far this season, tops are running well ahead with an average just over 25 degrees.
The relative absence of clouds is also evident in the rain gauge. The prospect of the odd shower over the weekend means the rain tally may yet get a late top-up. Heading into the weekend, just 4.8 millimetres had been registered at the bureau’s Observatory Hill site.
Depending on the timing of Monday’s predicted 2-10 millimetres of rain – the monthly cut-off point for rain is 9am on the last day of the month – Sydney could notch one of its five driest Mays in records going back to the 1850s.
The other especially dry years were 2008, when just three millimetres landed at the main city site in a month when the average rainfall is just under 120 millimetres. Other dry years include 1957, with 3.7 millimetres, 1860 with 4.5 millimetres and 1885 with 5.2 millimetres.
Nationally, rainfall has also been below-average during the past 12 months, says Karl Braganza, head of climate monitoring at the bureau. The big El Nino event in the Pacific – in which the usual westward-blowing winds stall or reverse – was one big influence on the reduced rainfall tallies.
The good news for farmers is that the breakdown of the event points to an improving outlook “The recorded rainfall pattern for May is certainly looking less El Nino-like, and the bureau’s seasonal outlook suggests a higher probability of above-average rainfall over the next few months,” Dr Braganza says.
El Nino and global heat
The El Nino gave a spike to global temperatures as the altered wind patterns meant a massive area of the Pacific took in less of the extra building up in the atmosphere, thanks mainly to rising levels of greenhouse gases.
Monash University’s Neville Nicholls – this week inducted as a fellow of the Australian Academy of Science for his research on climate variability – has highlighted how the recent El Nino compared with the two other huge events in 1982-83 and 1997-98. (See chart below of above-average temperatures in degrees as measured in a key region of the equatorial Pacific.)
“You can see that they are all about the same intensity – and they all show a similar life cycle,” Professor Nicholls said.
As a second chart (see below) of NASA’s global surface temperatures shows, however, the baseline for when the event starts is rising, pointing to the background warming from climate change.
“So the 1997/98 event is about 0.3 degrees warmer than the 1982-83 event, and the 2015-16 event is about 0.5 degrees warmer than the 1997-98 event,” Professor Nicholls said.
“While strong El Nino events don’t appear to be getting more intense or more frequent, they are starting out at a higher background global mean temperature,” he said. “So the reason we have seen record global temperatures over the past 12 months is not because the El Nino was especially strong, but because global warming had ‘lifted’ the baseline temperature.”
Data from the Bureau of Meteorology supports Professor Nicholls’ analysis. Australia’s temperatures have increased almost 1 degree in the past century, in line with much of the planet.
Even with Australia’s famously variable climate, cooler-than-average months are becoming increasingly rare. For instance, since August 2012, all but three months – February 2014, April 2015 and May 2015 – have been warmer than average, Dr Braganza said.
“This period also includes Australia’s top two warmest months on record,” he said. October 2015 was 2.89 degrees warmer than the 1961-90 average, based on mean temperatures, and September 2013 was 2.66 degree warmer.
The rolling 12-month period is also particularly warm.
“Based on temperatures to date, the period of June 2015 to May 2016 will be the warmest on record for that particular 12-month period – and it will be amongst the warmest for any 12-month period on record, depending on the weather during the last week of May,” Dr Braganza said.