Subjectively 2015 seemed like a very hot year, so there may be some surprise to find that according to the BOM’s Annual climate statement 2015 it was only the fifth hottest year. That’s possibly because the October-December period was the hottest on record. There was exceptional heat early in October, with parts of Victoria being 7°C above normal. Nationally October was 2.89°C above the 1961-90 average, a record monthly anomaly.
This graph shows the hot spells for the year:
This graph (from this site) shows the monthly anomalies for the last five years:
We can see that 2013 was consistently hot. In fact 2013 was the record year. 2015 comes in close behind 2013, 2005, 2014 and 1998, as we see in this graph:
So 2013-2015 were three of the five hottest years. Eight of the 10 warmest years have occurred since 2002.
This map shows where the heat was in terms of deciles.
Much of the continent was either decile 10 or the hottest on record.
The Australian mean rainfall for 2015 was 5% below the 1961–1990 average, with the Northern Territory and New South Wales above average.
There were three significant dry areas – the southwest of Western Australia, much of Queensland, and an area in the southeast encompassing Tasmania, most of Victoria and much of the settled areas in South Australia:
At Climate Central John Upton points out that in 2014 a flip was detected in the sluggish and elusive ocean cycle known as the Pacific Decadal Oscillation, or PDO. The shading in this graph represents cooler and warmer phases of the PDO against global temperatures:
The black line represents the 10-year running average.
It is quite noticeable that warming took off in the mid-1970s. Then we had a slow-down from 1998, known as the “pause” that really wasn’t a statistical pause. It looks as though it may have stepped up a gear in the last couple of years.
- The record warmth set in 2014 was surpassed again in 2015, when global temperatures surged to 1°C (1.8°F) above pre-industrial averages, worsening flooding, heatwaves and storms.
As the article says:
- The effects of the PDO on global warming can be likened to a staircase, with warming leveling off for periods, typically of more than a decade, and then bursting upward.
“It seems to me quite likely that we have taken the next step up to a new level,” said Kevin Trenberth, a scientist with the National Center for Atmospheric Research.
There is some discussion about the validity of the PDO concept, or whether it is just a label reflecting the predominance of El Niños and La Niñas. Nevertheless the direction is up and the line seems to surge at times. Like now.
Update: I’ve added an image of the early October temperature anomalies from this post by two Australian scientists: