As the heavens opened up on a dry NSW North Coast landscape this week, many are still recovering from the hottest spring on record, and the driest November, wondering how relevant climate events such as La Nina are anymore.
The November seasonal outlook for NSW from the Department of Primary Industries says the forecasts indicate "moderate to high probabilities of above median rainfall across NSW over the next three months" and that " a La Nina event has established and will likely persist into February 2021".
Only 10 per cent of NSW is now in drought or drought-affected after the drought recovery continued, the DPI says.
But just at summer's heels was one of the most extraordinary hot springs the nation and NSW has seen, with both maximum and minimum temperature records broken in many sites.
Spring ended with an extreme heatwave and the temperatures recorded on November 28 and 29 broke many records, some decades old.
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One of Australia's leading atmospheric scientists, Professor David Karoly, says that analysis shows the high variance in spring temperatures can only be explained by climate change and more carbon dioxide in the atmosphere.
Prof Karoly has been working with world climate data all his career, but recent work, collaboratively using data from over 20 world weather sources, has enabled he and his team to tell within a short time how much a season or year has exceeded the possible natural variance.
The high variance on this spring's temperatures could only be explained by climate change, he says.
"It was our record hottest and driest November," he says. Within a week his team had adduced it was not a possible spring variance within the data set compiled from century-old records.
"Climate change was the major contributor to the new record spring temperature, contributing about 1.5 °C to the observed anomaly of 2.4 °C," his team found.
"Both the observations and the climate model data show that the record 2020 spring temperature across Australia would have been virtually impossible without human-caused climate change.
"Even more remarkable is that Australian temperatures in spring were affected by the current La Nina event. These events are normally associated with colder than normal temperatures across Australia, such as in 2010, which was the most recent strong La Nina event.
"The global warming influence in spring due to higher greenhouse gases was able to overcome the cooling influence of La Nina".
In other words, Prof Karoly, says climate change is also changing how La Nina works - and that is totally new territory.
Prof Karoly is leader of the Earth Systems and Climate Change Hub within the National Environmental Science Program (NESP).
He said there was no doubt that extreme events would increase and that the chances of setting new records will only increase until 2050, unless climate change is reversed.
"The evidence is that from 2010 to 2020, it's getting hotter and hotter, and that will happen for at least the next 30 years or more unless we reduce emissions."
It will mean drier winters and wetter mid-summers.
The Bureau of Meteorology said Australia had gone through a spring never seen before.
It found it was Australia's warmest spring on record,
- mean maximum temperature and mean minimum temperature both warmer than average for virtually all of Australia
- Spring rainfall slightly below average for Australia as a whole
- Rainfall for the season was below average for much of eastern Queensland, north-eastern New South Wales, and western Tasmania.
- Spring 2020 was the warmest on record for Australia, coming in with a mean temperature 2.03 °C above average, well above the previous record (+1.81 °C in 2014). The national mean maximum temperature was the fifth-warmest on record at 2.14 °C above average, while the mean minimum temperature was the warmest on record at 1.91 °C warmer than average (previous record 1.46 °C in 1998).
In NSW many weather records were broken. It found that many locations had their highest spring mean daily minimum temperature on record or highest for at least 20 years.
"The spring mean temperature was the fifth warmest on record, and minimum temperatures were the warmest since 1914."
Menindee, Broken Hill, Moree and Albury all had their highest recorded spring temperatures, while Coonabarabran, Glen Innes, Cobar and Bellambi (Wollongong) had their highest spring minimums ever recorded.
Sydney also recorded its two hottest consecutive days (for any period) since 1960.