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Emergency crews tackle a bushfire at Boggabri, one of dozens across NSW during the heatwave. AAP Image/NEWZULU/Karen Hodge

The heatwave that engulfed southeastern Australia at the end of last week has seen heat records continue to tumble like Jenga blocks.

On Saturday February 11, as New South Wales suffered through the heatwave’s peak, temperatures soared to 47℃ in Richmond, 50km northwest of Sydney, while 87 fires raged across the state amid catastrophic fire conditions.

On that day, most of NSW experienced temperatures at least 12℃ above normal for this time of year. In White Cliffs, the overnight minimum was 34.2℃, breaking the station’s 102-year-old record.

On Friday, the average maximum temperature right across NSW hit 42.4℃, beating the previous record of 42℃. The new record stood for all of 24 hours before it was smashed again on Saturday, as the whole state averaged 44.02℃ at its peak. At this time, NSW was the hottest place on Earth.

A degree or two here or there might not sound like much, but to put it in cricketing parlance, those temperature records are the equivalent of a modern test batsman retiring with an average of over 100 – the feat of outdoing Don Bradman’s fabled 99.94 would undoubtedly be front-page news.

And still the records continue to fall. At the time of writing, the northern NSW town of Walgett remains on target to break the Australian record of 50 days in a row above 35℃, set just four years ago at Bourke Airport.

Meanwhile, two days after that sweltering Saturday we woke to find the fires ignited during the heatwave still cutting a swathe of destruction, with the small town of Uarbry, east of Dunedoo, all but burned to the ground.

This is all the more noteworthy when we consider that the El Niño of 2015-16 is long gone and the conditions that ordinarily influence our weather are firmly in neutral. This means we should expect average, not sweltering, temperatures.

Since Christmas, much of eastern Australia has been in a flux of extreme temperatures. This increased frequency of heatwaves shows a strong trend in observations, which is set to continue as the human influence on the climate deepens.

It is all part of a rapid warming trend that over the past decade has seen new heat records in Australia outnumber new cold records by 12 to 1.

Let’s be clear, this is not natural. Climate scientists have long been saying that we would feel the impacts of human-caused climate change in heat records first, before noticing the upward swing in average temperatures (although that is happening too). This heatwave is simply the latest example.

What’s more, in just a few decades’ time, summer conditions like these will be felt across the whole country regularly.

Attributing the heat

The useful thing scientifically about heatwaves is that we can estimate the role that climate change plays in these individual events. This is a relatively new field known as “event attribution”, which has grown and improved significantly over the past decade.

Using the Weather@Home climate model, we looked at the role of human-induced climate change in this latest heatwave, as we have for other events before.

We compared the likelihood of such a heatwave in model simulations that factor in human greenhouse gas emissions, compared with simulations in which there is no such human influence. Since 2017 has only just begun, we used model runs representing 2014, which was similarly an El Niño-neutral year, while also experiencing similar levels of human influence on the climate.

Based on this analysis, we found that heatwaves at least as hot as this one are now twice as likely to occur. In the current climate, a heatwave of this severity and extent occurs, on average, once every 120 years, so is still quite rare. However, without human-induced climate change, this heatwave would only occur once every 240 years.

In other words, the waiting time for the recent east Australian heatwave has halved. As climate change worsens in the coming decades, the waiting time will reduce even further.

Our results show very clearly the influence of climate change on this heatwave event. They tell us that what we saw last weekend is a taste of what our future will bring, unless humans can rapidly and deeply cut our greenhouse emissions.

Our increasingly fragile electricity networks will struggle to cope, as the threat of rolling blackouts across NSW showed. It is worth noting that the large number of rooftop solar panels in NSW may have helped to avert such a crisis this time around.

Our hospital emergency departments also feel the added stress of heat waves. When an estimated 374 people died from the heatwave that preceded the Black Saturday bushfires the Victorian Institute of Forensic Medicine resorted to storing bodies in hospitals, universities and funeral parlours. The Victorian heatwave of January 2014 saw 167 more deaths than expected, along with significant increases in emergency department presentations and ambulance callouts.

Infrastructure breaks down during heatwaves, as we saw in 2009 when railway lines buckled under the extreme conditions, stranding thousands of commuters. It can also strain Australia’s beloved sporting events, as the 2014 Australian Open showed.

These impacts have led state governments and other bodies to investigate heatwave management strategies, while our colleagues at the Bureau of Meteorology have developed a heatwave forecast service for Australia.

These are likely to be just the beginning of strategies needed to combat heatwaves, with conditions currently regarded as extreme set to be the “new normal” by the 2030s. With the ramifications of extreme weather clear to everyone who experienced this heatwave, there is no better time to talk about how we can ready ourselves.

We urgently need to discuss the health and economic impacts of heatwaves, and how we are going to cope with more of them in the future.

We would like to acknowledge Robert Smalley, Andrew Watkins and Karl Braganza of the Australian Bureau of Meteorology for providing observations included in this article.

Sarah Perkins-Kirkpatrick receives funding from the Australian Research Council.

Andrew King receives funding from the ARC Centre of Excellence for Climate System Science.

Matthew Hale receives funding from the Australian Research Council.

Richard Higgins (Letters, 15 February) writes: “Farming is about maintaining the land in such a way as to support the animals and people who live upon it”. The late Tony King, professor of politics at Essex University, argued that all successful popular revolutions, good and bad, were accompanied by land reform and redistribution. One criticism of the EU levelled historically by the progressive, internationalist wing of the Labour party has been that the common agricultural policy encourages wasteful use of our common agricultural wealth. Max Weber, more than 100 years ago, showed that there was a relationship between the existence of large, capital-intensive farming estates and reliance on seasonal, immigrant labour.

When the inevitable leftwing reaction to this rightwing Brexit comes we would do well to consider how to reframe agriculture to involve a greater portion of the population and to ensure that a greater portion of our basic needs can be met at a local level rather than, as we seem to do at the moment, relying entirely on production for export and thus throwing ourselves open to the tempestuous nature of global commodity markets in the hope we can be saved by financial calculus alone.
Tom Muddiman
Southampton

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The Flinders Ranges were once a refuge from a changing climate. Shutterstock

Finding the optimum environment and avoiding uninhabitable conditions has been a challenge faced by species throughout the history of life on Earth. But as the climate changes, many plants and animals are likely to find their favoured home much less hospitable.

In the short term, animals can react by seeking shelter, whereas plants can avoid drying out by closing the small pores on their leaves. Over longer periods, however, these behavioural responses are often not enough. Species may need to migrate to more suitable habitats to escape harsh environments.

During glacial times, for instance, large swathes of Earth’s surface became inhospitable to many plants and animals as ice sheets expanded. This resulted in populations migrating away from or dying off in parts of their ranges. To persist through these times of harsh climatic conditions and avoid extinction, many populations would migrate to areas where the local conditions remained more accommodating.

These areas have been termed “refugia” and their presence has been essential to the persistence of many species, and could be again. But the rapid rate of global temperature increases, combined with recent human activity, may make this much harder.

Finding the refugia

Evidence for the presence of historic climate refugia can often be found within a species’ genome. The size of populations expanding from a refugium will generally be smaller than the parent population within them. Thus, the expanding populations will generally lose genetic diversity, through processes such as genetic drift and inbreeding. By sequencing the genomes of multiple individuals within different populations of a species, we can identify where the hotbeds of genetic diversity lie, thus pinpointing potential past refugia.

My colleagues and I recently investigated population genetic diversity in the narrow-leaf hopbush, a native Australian plant that got its common name from its use in beer-making by early European Australians. The hopbush has a range of habitats, from woodlands to rocky outcrops on mountain ranges, and has a wide distribution across southern and central Australia. It is a very hardy species with a strong tolerance for drought.

We found that populations in the Flinders Ranges have more genetic diversity than those to the east of the ranges, suggesting that these populations are the remnants of an historic refugium. Mountain ranges can provide ideal refuge, with species only needing to migrate short distances up or down the slope to remain within their optimal climatic conditions.

In Australia, the peak of the last ice age led to dryer conditions, particularly in the centre. As a result, many plant and animal species gradually migrated across the landscape to southern refugial regions that remained more moist. Within the south-central region, an area known as the Adelaide Geosyncline has been recognised as an important historic refugium for several animal and plant species. This area encompasses two significant mountain ranges: the Mount Lofty and Flinders ranges.

Refugia of the future

In times of increased temperatures (in contrast to the lower temperatures experienced during the ice age) retreats to refugia at higher elevations or towards the poles can provide respite from unfavourably hot and dry conditions. We are already seeing these shifts in species distributions.

But migrating up a mountain can lead to a literal dead end, as species ultimately reach the top and have nowhere else to go. This is the case for the American Pika, a cold-adapted relative of rabbits that lives in mountainous regions in North America. It has disappeared from more than one-third of its previously known range as conditions have become too warm in many of the alpine regions it once inhabited.

Further, the almost unprecedented rate of global temperature increase means that species need to migrate at rapid rates. Couple this with the destructive effects of agriculture and urbanisation, leading to the fragmentation and disconnection of natural habitats, and migration to suitable refugia may no longer be possible for many species.

While evidence for the combined effects of habitat fragmentation and climate change is currently scarce, and the full effects are yet to be realised, the predictions are dire. For example, modelling the twin impact of climate change and habitat fragmentation on drought sensitive butterflies in Britain led to predictions of widespread population extinctions by 2050.

Within the Adelaide Geosyncline, the focal area of our study, the landscape has been left massively fragmented since European settlement, with estimates of only 10% of native woodlands remaining in some areas. The small pockets of remaining native vegetation are therefore left quite disconnected. Migration and gene flow between these pockets will be limited, reducing the survival chances of species like the hopbush.

So while refugia have saved species in the past, and poleward and up-slope shifts may provide temporary refuge for some, if global temperatures continue to rise, more and more species will be pushed beyond their limits.

Matt Christmas does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond the academic appointment above.

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