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Tipping the seesaw

Australia's climate future

FOR A PLETHORA of reasons, 2020 will be etched in our memories forever. As I think back to January 2020, my heart skips a beat. I remember the sky laden with smoke and the pungent smell of burnt eucalypts. I remember taking my children for a swim to escape the intense heat but leaving the pool as quickly as we arrived once ash started to rain on the baby’s head. I remember the dreadful images from Mallacoota, people trying to escape the flames in the water and on the shoreline. Smoke engulfing our nation’s capital. Native animals desperately trying to flee with nowhere to go. The sheer and total devastation the fires created. Never-ending conversations with journalists where I remember using the word ‘unprecedented’ again and again to communicate just how bad these fires truly were.

The Australian summer of 2019–20 was undoubtably exceptional. 2019 was Australia’s warmest year on record,[i] hitting the previous warmest year (2013) right out of the park. Last summer was categorised by multi-year drought (2019 was also our driest year on record) and two phases of hemisphere-scale variability that typically mean hot and dry weather, a strongly positive Indian Ocean Dipole (IOD) event and a negative Southern Annular Mode (SAM). To give you a brief introduction, IOD is the difference in sea surface temperatures between the western and eastern tropical Indian Ocean and is typically active during winter and spring, when it governs rainfall and temperature over much of Australia. The SAM is the north–south shift in the westerly windbelt circulating Antarctica and can be active at any time of year. Depending on the time of year, a positive or negative SAM can mean different things for eastern Australian rainfall and temperature.

From my work as a climate scientist, I knew the combination of these factors with Australia’s long-term warming trend of 1.4 degrees was the perfect recipe for disaster. In addition to the catastrophic fires during the Black Summer, a litany of heat records were smashed. Nationally, the record for the hottest day was broken twice over two sequential days, 16 and 17 December 2019.

Fast forward to this current summer: at face value, it’s quite different. Instead of ash falling on my now two-year-old’s head, she has to deal with pouring rain to chase her elder sister around the backyard on their scooters. The IOD remained neutral throughout spring; as I write this, the SAM is in a positive phase, which, during summer, is associated with high rainfall across south-east Australia. We are also in the middle of the first La Niña – the sister to hot and dry El Niño – in almost a decade, which has recently lashed much of eastern Australia with rainfall. Although we had our warmest spring and November on record during 2020, the current summer has been no match for the one prior in the temperature stakes. With the recent rainfall and relatively cooler temperatures, it feels like it belongs at the other end of the spectrum.

Yet 2020 comes in at number four of Australia’s top five warmest years on record.[ii] Despite what feel like ‘chalk and cheese’ summers, the difference between the two years boils down to 0.37 degrees, and they’re separated on that list by the statistics from just another two years, 2005 and 2013. What’s more, the last eight years are all among the country’s top ten warmest across 110 years of consistent record-keeping.

Although it’s a cliché I like to avoid, Australia has always been ‘a land of drought and flooding plains’. We have always experienced a harsh climate, often seesawing between one extreme state and another across sequential years. In this way, 2019 and 2020 are textbook examples. However, as their rankings in Australia’s top five hottest years illustrate, climate variability now matters less, and anthropogenic climate change matters so much more.

If that’s not yet clear to you, I’ll be blunt: the presence of anthropogenic climate change on our unique and variable climate regime is becoming ever more apparent. The seesawing of Australia’s weather and climate has previously been dominated by multiple different phenomena, described in climate circles by the jargonistic mouthful ‘modes of climate variability’. I have already introduced you to the IOD, SAM and La Niña. Along with the Madden-Julian Oscillation (MJO) – a tropical pulse that circulates the globe and underpins the activity and intensity of the Australian monsoon – these are the main sources of variability that allowed Australia’s climate to fluctuate on timeframes that range from seasonal to inter-annual scales. While they all have their own typical phases and work on their own timelines, they can overlap and amplify each other. Cases in point include the current combination of La Niña and positive SAM, and the combination of 2019’s positive IOD and negative SAM.

Yet these modes no longer solely dictate the rocking of Australia’s climate seesaw. In a non-changing climate, variability would drive extreme conditions, tipping the seesaw up and down and decreeing which years were hotter or cooler than others. The most influential mode of climate variability on Australia is arguably the El Niño/Southern Oscillation known as ENSO, the parent to both El Niño and La Niña. This tightly coupled ocean/atmosphere phenomenon occurs in the Pacific Ocean and can cause fluctuations in the global climate as well as Australia’s. On average, we experience at least one El Niño and La Niña every two to seven years, associated with hotter and drier or cooler and wetter conditions, respectively, over at least two thirds to three quarters of the continent. These active phases of ENSO can last anywhere from a single summer to multiple consecutive years.

However, none of Australia’s top five warmest years have been driven by El Niño. While other climate modes such as the IOD and SAM played a clear role in the record-breaking conditions of 2019, the years 2005, 2013 and 2018 were characterised by their lack of dominant and extreme variability phases: they were extreme years without the usual drivers of extremity. Indeed, this was also the case for most of 2020: the establishment of La Niña by September should have brought average temperatures down for the rest of 2020, and certainly not have seen it take its place in the list of our top five record-warm years.

The tides have now turned. The drivers that have dominated Australia’s climate landscape for so long are now being overshadowed by the black sheep that is climate change. Every time variability attempts to govern the Australian climate like it used to, climate change steps in and takes total control.

No year illustrates this more profoundly than 2019. A long-term drought and extreme IOD and SAM phases certainly primed conditions for the year to be naturally hot. But without climate change, there is no way it would have been as hot as it was – a whopping 1.52 degrees above the 1961–90 average. Looking back prior to 2000, when the effects of climate change were less and the relative influence of variability was higher, Australia’s average temperature anomaly did not ever reach 1 degree hotter than the long-term average – not even during the 1997–98 El Niño, one of the strongest of the twentieth century.

Remember how I mentioned earlier that Australia’s national daily maximum temperature was broken two days in a row during December 2019? The odds of this sequence are practically impossible in a stable climate influenced only by natural variability.

The dominance of climate change over variability is also unmistakably evident in global temperatures. In 1956 – when a La Niña struck – global average temperature was 0.28 degrees lower than the 1961–90 average (La Niñas usually cool down global temperatures, as they do for Australia). This is a typical fluctuation that climate scientists would expect to see when variability is the prevailing climate driver. In 2011 – during the last La Niña – the global average temperature was 0.42 degrees higher than the 1961–90 average. Moreover, despite the establishment of a La Niña event towards the end of 2020, last year was the equal warmest year on record globally (tying with 2016).[iii] The last time global temperatures were below average was 1976 – and that was off the back of a multi-year La Niña.

I was born in the early 1980s. If I wasn’t a climate scientist, the cooling effect of La Niña would sound to me like a distant legend these days. It will sound even more distant to my girls as they grow up.

As 2019 and 2020 have also demonstrated, there will still be variability in our weather on yearly timescales under the supremacy of climate change. Climate change has placed years where variability favours warm conditions on steroids, while simultaneously stealing the welcome reprieve that traditionally cooler phases of climate variability used to provide. This begs the question: what will happen if even more extreme states of variability combine with fiercer climate change? The 2019 positive IOD was not the strongest in recent history. The most extreme positive IOD on the instrumental record occurred in 1997, and according to proxy records, there is evidence of an even stronger event during the seventeenth century.[iv] What will the impact be if and when events like these clash with climate change in the future?

 

PART OF ME is not at all surprised that climate change has taken control at this pace. Climate scientists have literally been banging on about this coming change for decades. My own research shows that just a small shift in average temperatures leads to disastrous changes in extreme heat. Despite Australia’s average temperature increasing by what I have heard some people call a modest amount (1.4 degrees for Australia; 1.1 degrees when globally averaged), we have already seen significant increases in the intensity, frequency and duration of heatwaves over most of Australia, as well as the rest of the world.[v] Other research by my colleagues finds that record-breaking heat extremes already outnumber cool extremes twelve to one.[vi]

The future looks a whole lot worse. Changes in heatwaves – not just over Australia, but everywhere – scale with global average temperature. The more global temperature rises, the more heatwaves we will see, the longer they will last and the hotter they will be.[vii] Global temperature was 0.95 degrees above the twentieth-century average in 2019. Depending on which emissions scenario we track, the planet could warm by more than 4 degrees by the end of this century. It’s not hard to work out what this means for extreme heat. For Australia, summers like our last will be more common than they are rare.

So along with my lack of surprise, I am equal parts exhausted and disheartened. I am not so much tired with the continual discussion on the domination of climate change; I am all too happy to talk about this with anyone who is genuinely interested. But I am drained – so drained – by this discussion falling on deaf ears, or worse, pushing non-acceptors of scientific evidence deeper into their black holes. I am fatigued by the petty response of our leaders to limit global warming to relatively tolerable levels. I used to think that perhaps they were allergic to science, but Australia’s response to COVID-19 has demonstrated that our state and federal governments can successfully implement scientific knowledge. This infuriates me a little: why aren’t they doing the same to overpower climate change?

My dismay takes a more personal tone. I have a vivid memory of attending a national conference when heavily pregnant with my first child and listening to a public health expert list all the impacts of extreme heat on our health in thirty to forty years. I rubbed my belly, realising that my daughter would be my age around that time. I was so saddened to learn about the ailments that she – along with her peers – would experience, caused by actions and activities they hadn’t participated in. If I struggled to take the dog for a walk or hang out the washing because of the debilitating combination of pregnancy and extreme heat, how will she cope with pregnancy during even hotter summers? Will she even choose to have children under the tighter grip of climate change? I am enraged that her generation will inherit a world in far worse condition than the one we inherited – how is that even remotely fair?

I think it is impossible to be a climate scientist and not be at least a little jaded about where and who our collective knowledge is (or isn’t) reaching. The overbearing dominance of climate change is not news. And it is no longer a problem for the future; it is happening now. But I also think most of us still have a level of optimism that more will happen to subdue the influence of climate change – and hopefully sooner rather than later. If our leaders are listening to health experts and using cutting-edge medical technology to battle Covid, then perhaps, one day, they’ll start listening to us, too? In any case, I have my fingers and toes crossed that we don’t need any more black summers to spark such a revolution.

 

References

[i] http://www.bom.gov.au/climate/current/annual/aus/ (accessed 11 January 2021)

[ii] http://www.bom.gov.au/climate/current/annual/aus/#tabs=Overview (accessed January 2021)

[iii] https://climate.copernicus.eu/copernicus-2020-warmest-year-record-europe-globally-2020-ties-2016-warmest-year-recorded (accessed 11 January 2021)

[iv] Abram, N.J., Wright, N.M., Ellis, B., Dixon, B.C., Wurtzel, J.B., England, M.H., Ummenhofer, C.C., Philibosian, B., Cahyarini, S.Y., Yu, T.L. and Shen, C.C., 2020, Coupling of Indo-Pacific climate variability over the last millennium, Nature579(7799), pp. 385–392.

[v] Perkins-Kirkpatrick, S.E. and Lewis, S.C., 2020, Increasing trends in regional heatwaves, Nature Communications11(1), pp. 1–8.

[vi] Lewis, S.C. and King, A.D., 2015, Dramatically increased rate of observed hot record breaking in recent Australian temperatures, Geophysical Research Letters42(18), pp. 7776–7784.

[vii] Perkins-Kirkpatrick, S.E. and Gibson, P.B., 2017, Changes in regional heatwave characteristics as a function of increasing global temperature, Scientific Reports7(1), pp. 1–12.

 


This article is part of The Elemental Summer, an online series featuring writing from a selection of Australia’s most respected thinkers on climate. 

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