Sometime before 8am on another soaking morning, Sydney recorded its average annual rainfall just four months into the year. This current deluge is now adding to a growing pool of evidence gathered by scientists showing that weather patterns are shifting as the climate warms, leaving Australia’s east coast generally hotter and dryer, at least until the rain sets in.
CSIRO Climate Science Centre director Jaci Brown said while La Nina has been a major driver for the wet weather and added more energy to the system, climate change was also contributing. She said that for every degree of warming, the atmosphere can hold an additional 7 per cent more moisture.
“It’s not surprising that when the rain comes, there is more to it – it is more intense,” she said.
Despite the ongoing summer and autumn deluges this year, in Greater Sydney annual rainfall has decreased by 9 per cent in the last 30 years, particularly in late winter and spring, 2019 data from the Bureau of Meteorology and CSIRO found. It’s a trend that climate scientists have observed across south-east Australia, where there has been a decline of around 12 per cent in rainfall during April to October since the late 1990s.
It comes as Sydney has passed its mean annual rainfall of 1213mm, only four months into the year. The total rainfall for the city now stands at 1223.8mm.
Ms Brown said there had been distribution changes in the annual rainfall, with intensifying summer rainfall and winter rains decreasing along the south-east of Australia.
She added that there are certain things that climate scientists can predict – such as how greenhouse gases will drive increasing temperatures – there was still a lot of uncertainty as to what the future will look like.
The oceans are one of the most important indicators of climate change playing out as they absorb a lot of the carbon dioxide and heat from the atmosphere, driving more acidic water, faster melting ice sheets and increasing sea levels. This in turn will continue driving out weather systems, making them more extreme.
University of Melbourne senior lecturer in climate science Dr Andrew King said that in the past few decades, the number of heatwaves on land and in the ocean had increased, while snow cover in the Australian Alps had decreased. These changes were impacting a variety of ecosystems, including in parts of Tasmania where it had become easier to grow certain types of grapes used in wine production.
He added that during extreme weather events, like the 2019-20 Black Summer bushfires, the impacts of climate change were evident. “For many, the Black Summer bushfires and extreme heat was a wake-up call that showed how bad Australian summers could be in the future,” he said.
Temperatures across Australia have increased by between 0.2 and 1.6 degrees on average over the past 21 years, according to the latest NASA data. Most of the warming has occurred since 1950.
Of the nine warmest years on record, seven of these were 2013-2019, with 2019 the warmest. But if the global average temperature increases to 1.5 degrees higher than it was during the period 1850-1900, then years like 2019 will become an average year.
The wet weather is expected to linger for the next few weeks as La Nina begins to weaken and we enter the east coast low peak season, but whether the wet weather will return later this year is yet to be decided. Modelling by the National Oceanic and Atmospheric Administration (NOAA) shows a third La Nina or a neutral phase could be possible next summer. Both the El Nino and La Nina are ends of a weather spectrum, while neutral is in the middle of the two. They are collectively known by scientists as the El Nino-Southern Oscillation (ENSO).
However, the NOAA model is just one that meteorologists use to predict climate drivers with both the Australian and European models showing a neutral phase was more likely. Meteorologists will get a better idea of the ENSO modelling after winter.
It comes as the goal of holding global warming to 1.5 degrees is no longer likely to be achieved, the latest report of the United Nations chief climate body warns, and that the window to achieving the goal is closing fast.
The report by the Intergovernmental Panel on Climate Change (IPCC), published early on Tuesday morning Australian time, notes that limiting warming to 1.5 degrees would require global greenhouse gas emissions to peak before 2025 at the latest and fall by 43 per cent by 2030. At the same time, methane also needs to be reduced by about a third, the IPCC said in a statement.
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