Jonathan Nott, James Cook UniversityTropical Cyclone Seroja battered parts of Western Australia’s coast on Sunday night, badly damaging buildings and leaving thousands of people without power. While the full extent of the damage caused by the Category 3 system is not yet known, the event was unusual.
I specialise in reconstructing long-term natural records of extreme events, and my historic and prehistoric data show cyclones of this intensity rarely travel as far south as this one did. In fact, it has happened only 26 times in the past 5,000 years.
Severe wind gusts hit the towns of Geraldton and Kalbarri – towns not built to withstand such conditions.
Unfortunately, climate change is likely to mean disasters such as Cyclone Seroja will become more intense, and will be seen further south in Australia more often. In this regard, Seroja may be a timely wake-up call.
Cyclone Seroja initially piqued interest because as it developed off WA, it interacted with another tropical low, Cyclone Odette. This rare phenomenon is known as the Fujiwhara Effect.
Cyclone Seroja hit the WA coast between the towns of Kalbarri and Gregory at about 8pm local time on Sunday. According to the Bureau of Meteorology it produced wind gusts up to 170 km/hour.
Seroja then moved inland north of Geraldton, weakening to a category 2 system with wind gusts up to 120 km/hour. It then tracked further east and has since been downgraded to a tropical low.
The cyclone’s southward track was historically unusual. For Geraldton, it was the first Category 2 cyclone impact since 1956. Cyclones that make landfall so far south on the WA coast are usually less intense, for several reasons.
First, intense cyclones draw their energy from warm sea surface temperatures. These temperatures typically become cooler the further south of the tropics you go, depleting a cyclone of its power.
Second, cyclones need relatively low speed winds in the middle to upper troposphere – the part of the atmosphere closest to Earth, where the weather occurs. Higher-speed winds there cause the cyclone to tilt and weaken. In the Australian region, these higher wind speeds are more likely the further south a cyclone travels.
Third, most cyclones make landfall in the northern half of WA where the coast protrudes far into the Indian Ocean. Cyclones here typically form in the Timor Sea and move southward or south-west away from WA before curving southeast, towards the landmass.
For a cyclone to cross the coast south of about Carnarvon, it must travel a considerable distance towards the south-west into the Indian Ocean. This was the case with Seroja – winds steered it away from the WA coast before they weakened, allowing the cyclone to curve back towards land.
My colleagues and I have devised a method to estimate how often and where cyclones make landfall in Australia.
As cyclones approach the coast, they generate storm surge – abnormal sea level rise – and large waves. The surge and waves pick up sand and shells from the beaches and transport them inland, sometimes for several hundred metres.
These materials are deposited into ridges which stand many metres above sea level. By examining these ridges and geologically dating the materials within them, we can determine how often and intense the cyclones have been over thousands of years.
At Shark Bay, just north of where Seroja hit the coast, a series of 26 ridges form a “ridge plain” made entirely of one species of a marine cockle shell (Fragum eragatum). The sand at beaches near the plain are also made entirely of this shell.
The ridge record shows over the past 5,000 years, cyclones of Seroja’s intensity, or higher, have crossed the coast in this region about every 190 years – so about 26 times. Some 14 of these cyclones were more intense than Seroja.
The record shows no Category 5 cyclones have made landfall here over this time. The ridge record prevents us from knowing the frequency of less intense storms. But Bureau of Meteorology cyclone records since the early 1970s shows only a few crossed the coast in this region, and all appear weaker than Seroja.
So why does all this matter? Cyclones can kill and injure people, damage homes and infrastructure, cause power and communication outages, contaminate water supplies and more. Often, the most disadvantaged populations are worst affected. It’s important to understand past and future cyclone behaviour, so communities can prepare.
Climate change is expected to alter cyclone patterns. The overall number of tropical cyclones in the Australian region is expected to decrease. But their intensity will likely increase, bringing stronger wind and heavier rain. And they may form further south as the Earth warms and the tropical zone expands poleward.
This may mean cyclones of Seroja’s intensity are likely to become frequent, and communities further south on the WA coast may become more prone to cyclone damage. This has big implications for coastal planning, engineering and disaster management planning.
In particular, it may mean homes further south must be built to cope with stronger winds. Storm surge may also worsen, inundating low-lying coastal land.
Global climate models are developing all the time. As they improve, we will gain a more certain picture of how tropical cyclones will change as the planet warms. But for now, Seroja may be a sign of things to come.
This article is part of Conversation series on the nexus between disaster, disadvantage and resilience. Read the rest of the stories here.
Cheryl Durrant, UNSWClimate change is a hot topic in Australian security circles, as it poses an emerging threat to our national resilience and way of life. As a new report from the Australian Strategic Policy Institute (ASPI) last week warned, the federal government is unprepared to meet these challenges.
The report, authored by Dr Robert Glasser, said the government has largely overlooked the security threat posed by rising seas, climate-induced famine, extreme weather events, mass migrations and other climate change damage in Southeast Asia. Australia is sitting on the frontline of this vulnerable region.
Glasser’s report focuses on Southeast Asia, but in the bigger picture, climate security is an existential global risk which the Australian government is yet to fully grasp. It is this global aspect of climate and security which will be on the agenda in two weeks time at the Biden Leaders Summit in the US.
The global risk is broader than traditional security threats, such as the rise of China, terrorism and separatist movements. As the ASPI report emphasises, there is a relationship between climate security and other sectors such as food, health and environmental security.
Unlike traditional national security threats, climate threats have no respect for national or sector borders and cannot be solved with missiles.
The threat is urgent. With the end of the Donald Trump presidency, climate change is back on regional and international security action agendas. The penny has dropped on how little time is left to take action to prepare for the worst of consequences.
This is especially the case when there are long lead times to implement action, such as infrastructure development and military capability development.
ASPI’s key recommendations to the government include:
These make sense, as the first step of preparedness is understanding the risk.
The ASPI report notes Southeast Asia “has the world’s highest sea-level rise per kilometre of coastline and the largest coastal population affected by it”. The region is a hot spot for cyclones, with some nations vulnerable to catastrophic heat or fires.
The ASPI report notes:
Those hazards will not only exacerbate the traditional regional security threats […] but also lead to new threats and the prospect of multiple, simultaneous crises, including food insecurity, population displacement and humanitarian disasters that will greatly test our national capacities, commitments and resilience.
The report focuses on Southeast Asia and natural disasters, but the risks and the affected regions are bigger than that.
The Indo-Pacific region may see the displacement of millions of people due to climate change-related extreme weather events, heatwaves, droughts, rising seas and floods. We’re already seeing this occur in Bangladesh and small island developing states.
We could also see conflict arise as climate change affects global food or water resources. A particular concern is the potential geopolitical tensions between India and China over dwindling Tibetan water resources.
Urgency and risk are central to an executive order from President Joe Biden in January. The order requires a US national security estimate on the economic and national security impacts of climate change by June. The US Department of Defence must also complete an analysis of the security implications of climate change in the same timeframe.
Most tellingly, the US is taking an integrated approach to climate security. Foreign policy, defence and economic risk analysis are being conducted in a joined-up, systemic way.
In contrast, the Australian Defence Strategic Update 2020 was conducted in isolation from foreign policy and economic reviews. Taking a narrow military perspective, it does mention climate change, but only once, as a subset of human security threats.
Australia risks being left behind as other countries follow the US lead. Across the Tasman, our Kiwi friends are already well advanced in turning risk awareness into action. The New Zealand government completed its first national climate risk assessment last year, with a national adaptation plan to be completed by August 2022.
Being left behind has consequences for Australia’s international standing, national resilience and economic position.
From a diplomatic perspective, Australia’s influence in the Indo-Pacific region is diminished, relative to other actors, especially in states where climate change risk is a top priority, such as Vanuatu or Kiribati.
Risks offer opportunities as well. For example, Australia has an abundance of critical minerals and rare earths needed for modern communications, space technologies, and renewable energy generation and transmission. These are key for business, as well as critical for defence forces.
However, processing and manufacturing is largely conducted offshore — in countries vulnerable to climate risks such as Malaysia — before returning to Australia as finished products.
This puts Australian defence and space and energy sectors at risk of disruption, and Australian businesses at risks of economic loss.
ASPI’s report echoes the earlier recommendation from a 2018 Senate inquiry into the implications of climate change for Australia’s national security. The inquiry also called for a coordinated whole-of-government response to climate change risks.
Three years later, the federal government has yet to act on its recommendations.
The Australian government now needs to have a greater sense of urgency to act on the growing national and international calls to act on climate risk. But first, our leaders need a changed mindset. They must accept that climate change is an immediate threat to Australia.