La Nina leads to cool summer, still hotter than average | Alds

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La Nina leads to cool summer, still hotter than average


This summer was our wettest for five years and the coolest in a decade, due mostly to La Nina shaking up Australia’s climate.

That’s according to the Bureau of Meteorology (BOM) which released it’s summer climate review today.

It’s undoubtedly good news for a country that has been ravaged by drought and bushfires.

But a small detail in the flurry of data released by the BOM is sobering, climate watchers, have said.

After the dry and scorching summer weather of 2019/20, the hallmark of which was huge bushfires, this year’s season was remarkable for how wet and non-scorching it was.

Since 1900, there have only been three years that have seen a wetter December than the one last year. Overall, rainfall across the continent during this summer was the highest since 2016-17.

In New South Wales, that rain was 29 per cent above the long term average (measured between 1961 and 1990) and the wettest since 2011/12, making it the soggiest state.

Queensland saw 8 per cent more rainfall but, rarely across Australia this summer, it also saw below average moisture in some areas around the Capricornia, Wide Bay and Burnett regions.

All this rain has largely been fuelled by the La Nina climate driver which bubbled up in the Pacific and pushed warmer water towards eastern Australia.

The mercury also took a dive. This summer was the coolest since 2011/12.

Melbourne had its chilliest summer since 2004/05 with Brisbane, Sydney and Canberra seeing the coldest such season for a decade.

CHART SHOWS TROUBLING TREND

The BOM has helpfully published a chart that details how each summer’s overall temperatures performed against the average, as measured from 1961-1990. You can have a look at this below.

Red bars are summers where the difference between the actual temperature and the average temperature, known as the anomaly, is higher. Essentially, hotter than average summers.

The blue bars are the opposite: summers where it was cooler than average.

If you look at the updated chart, which included this current summer, you’ll see a huge drop in that temperature anomaly from 2019 when the mercury was approaching 2C above average. In 2018, the anomaly was even higher, above 2C.

In 2020, that anomaly was far smaller. Temperatures were just 0.06C above the average. You can see that little spike below.

And that’s the big issue: on the coldest summer for a decade, aided by a strong La Nina, and with one of the coolest Decembers for more a century, the average summer temperature in Australia was still above the baseline.

If any summer was to finally see temperatures dip below average, it was the summer we’ve just had.

It didn’t happen. It was still warmer than it should be.

LA NINAS GETTING HOTTER

Professor David Holmes from the Monash University Climate Change Communication Research Hub (MCCCRH) said it was a clear and troibling sign that even Australia’s cold summers were now actually quite warmer.

“La Nina summers are, on average, 0.36C cooler than average for all summers.

“But like all summers, La Nina summers have been warming,” he said.

“As the observations show, they have warmed by 1.1C since 1949 while all summers have warmed by 1.4C.”

Back in December, Monash University climate scientist Dr Ailie Gallant told news.com.au she was “in shock” at how hot Australia’s run up to summer was, despite it being a La Nina year.

November 2020 was the hottest Australia had ever seen.

“Typically late spring and early summer is when we have the strongest signal for La Nina episodes. They typically should be cooler than the years around them so to have the hottest November on the record, well I’m blown away by the whole situation. I’m actually in shock.”

Temperatures did indeed drop going into December. However, not by enough to stop the season being warmer than average.

In Western Australia, there is another worrying sign about where our climate is headed.

A rare and potentially damaging climate phenomenon has caused temperatures to soar in the waters off the WA coast.

A type of maritime heatwave, dubbed a “Ningaloo Nino,” has been increasing in frequency.

The heating occurs during La Nina years when warmer water from the Pacific travels between northern Australia and the Indonesian archipelago and ends up joining with a current, called the Leeuwin Current. The warm water then travels down the entire coast of WA.

The UNESCO world heritage listed Ningaloo Reef, off the coast near Exmouth, can experience significant coral bleaching during these heatwaves. Some fisheries can wane and seagrasses often die.

A brief by the Monash University Climate stated there was a “growing risk” of more marine heatwaves due to the rising overall temperature trend.

While bleaching had not been as bad this year as in 2011, the increase in temperatures means it’s becoming more of a common event.

“The observations show us that, over the past 40 years, waters around the Ningaloo Reef have warmed much faster than most other surrounding Australian waters in summer”, MCCCRH’s Prof Holmes.

“Climate projections suggest that more frequent and intense marine heatwaves can be expected in the future.”

Meteorologists say that it’s likely La Nina has now reached its peak and we could be back into the neutral phase of the El Nino Southern Oscillation (ENSO) by May.

Until then, increased rain is still likely. But the long term forecast will see the mercury rise as we go trough March and April. The rain gauge will also only get emptier as we head into a neutral ENSO, possibly swinging to El Nino.



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