It’s the crisis that could cost health authorities upwards of $6 billion and cause an extra 250,000 deaths per year by 2030.
The World Health Organization (WHO) says climate change has emerged as a “fundamental threat to human health”.
“Health professionals worldwide are already responding to the health harms caused by this unfolding crisis,” the organisation says.
“It threatens the essential ingredients of good health — clean air, safe drinking water, nutritious food supply and safe shelter — and has the potential to undermine decades of progress in global health.”
Already in Australia, scientists say they are beginning to see the impact of global warming on people’s overall health.
A case of Japanese encephalitis virus was recently discovered in northern Western Australia — “unusually early in the season for mosquito-borne viruses to be active”, according to health authorities.
Researchers said pollen seasons were becoming longer and the number of Australian hay fever sufferers was expected to grow by 70 per cent over the next three decades.
And as Australia braces for another searing summer, experts say it is becoming impossible to ignore the crisis bearing down on the nation.
Gastro
Gastroenteritis is an infectious disease that can be passed through food and water, and between people.
Australia has experienced an explosion in cases in the last year — an anomaly scientists believe is in part due to climate change.
Dr Elizabeth Elliott said the recent figures of cryptosporidium — a parasite that causes gastro-like symptoms — indicated a potential causal link between the illness and exposure to water.
“We don’t know the reason for the upswing … however, we do have some potential explanations in that the infection rate of gastro does increase in summer months or in warmer climates,” she said.
“Infection is primarily happening due to contact with water, swimming pools, spas, lakes … [cryptosporidium] can stay in the water for some time.”
Dr Elliott said summer months and increased heat meant more people were seeking out water to cool off in.
She said stagnant water also made it easier for the parasite to spread.
Other types of gastro including rotavirus and norovirus have also been linked to increases in temperature and changing environments.
A recent study by the University of Edinburgh said instances of flooding normally preceded rising case numbers.
“Outbreaks of leptospirosis, campylobacter and cryptosporidiosis have all been reported because of climate change-related flooding,” the study said.
“On the other hand, rotavirus and norovirus may decrease in a global warming environment because these viruses survive less well at warmer temperatures.”
Climate change can make it harder to access clean water and nutritious food, and extreme weather events like heatwaves can see people seek out bodies of water.
Dr Elliott said it was important for authorities to take note of the spike, and plan for it.
“I think it’s really important for governments and policymakers and health departments to be looking at these figures,” she said.
“The thing about gastro and any other common infections is that they take a great toll on society.
“If your child is sick and you don’t keep them home from preschool, they give it to the rest of the preschool, and they then give it to all of their families.
“It just seemingly goes on for weeks, and of course, parents often have to stay at home to mind their children, so there’s lost productivity and cost to society.
“I think when we can use measures to control infectious diseases, we should be doing that.”
Dr Elliott said it was important to vaccinate children against rotavirus and familiarise yourself with how gastro can present in small children.
Mosquito-borne illnesses
Cases of mosquito-borne illnesses including Ross River virus and Dengue fever have previously been detected in Australian patients.
Senior medical entomologist at the University of Townsville Dr Scott Lyons says cases of Malaria and Zika virus are more commonly picked up when people travel overseas to humid or wet climates.
“[Mosquitos] are cold-blooded animals and can’t regulate temperature, so they really like that warm and damp sort of environment,” he said.
However, a Japanese encephalitis virus detection in northern Western Australia and another case in Victoria has scientists concerned about the future of mosquito breeding seasons.
“An increase in temperatures that leads into the winter months means mosquitoes have a longer time [to breed],” Dr Lyons said.
“You’ll get an explosion in numbers [over summer] but normally as the water dries up in dry seasons in northern Australia, populations go down.
“But if you’ve got higher temperatures for longer and warm water sitting around for longer, you’ve got more mosquitoes and more virus circulating.”
Dr Lyons said recent weather had resulted in a bigger population than normal in some parts of the country.
“Probably about two years ago, we saw quite a few human cases [of Japanese encephalitis] down around southern Australia, which we’ve never really had before,” he said.
“We think it’s because of a good couple of years of flooding through central Queensland.”
Dr Lyons said changes in waste management, proper water storage and an increased availability of repellent had been effective ways to avoid mosquito-borne illnesses, but it might be more difficult as Australia’s climate changed.
“If you’re looking at climate change, even the basics as increasing in temperature … mosquitoes very dependent on temperature and humidity,” he said.
“The warmer and more humid it is, they’ll develop quicker and faster and be bigger and stronger.”
Heat stroke
One of the more obvious illnesses expected to be impacted by rising temperatures is heat stroke.
While heat stroke alone can cause headaches, nausea, rapid breathing and pain, it also exacerbates pre-existing conditions such as heart conditions and hypertension.
Dr Thomas Longden from Western Sydney University estimated in a 2019 study that about 36,000 people lost their lives between 2006 and 2017 due to heat-related causes.
“For most healthy people, getting caught out in the heat means they’ll get dehydrated and suffer all the things that come with that,” he said.
“But for someone that already has some health issues that impact the body’s ability to firmly regulate their temperature, getting caught out in the heat means that a critical event can be escalated.
“And a lot of people don’t realise that even diabetes can mean that people have difficulty regulating their heat.”
According to the National Centers for Environmental Information’s 2023 climate report, last year was the warmest year on record — 1.35 degrees Celsius hotter than the pre-industrial average.
Australia has already experienced record-breaking heatwaves over the last two summers, and experts predict they will last longer and become more intense over time.
Dr Longden said there was no real, accurate data around heat-related mortality from 2017 onwards.
He said as climate change altered heat wave patterns, it was crucial to adapt and better communicate risks to vulnerable populations, including targeted outreach and support for those at risk during heatwaves.
“I think that if we do not track or record heat-related deaths, then there is the danger that we become more complacent,” he said.
“Australia is so big that the types of heatwaves that impact different regions are quite different … ahead of the summer, I think what we need to be more aware of is that the different types of heatwaves may impact people differently.
“We don’t want to be complacent, and we don’t want to make assumptions about who is more or less vulnerable to heat-related exposure.”
Mental illness
Health authorities often report a spike in mental illness reports following extreme weather events.
Services in northern New South Wales were in demand following disastrous floods in early 2022, and eventually triggered a scheme by the federal government to help treat those with post-disaster PTSD.
The frequency of natural disasters is expected to increase as climate change worsens, and Dr Chloe Watfern from the Black Dog Institute said eco-anxiety was a real problem amongst Australians.
“We’re absolutely already seeing the impacts of climate change on mental health, from bushfire survivors experiencing trauma to young people grappling with eco-anxiety,” she said.
“There’s even compelling evidence that increased average temperatures are associated with more people presenting to emergency departments with suicidal thoughts and behaviours.
“We’re experiencing these impacts on mental health right now, but then everything suggests that these impacts will also intensify over time.”
Dr Watfern said the Black Dog Institute often heard from people struggling to cope with the impact of climate change on their mental health.
“People tell me they feel powerless, anxious and sometimes overwhelmed,” she said.
“Parents worry about their children’s future, their grandchildren’s future.
“Environmental scientists have described the emotional toll of observing the effect of climate change on places or species or earth systems.
“Young people express deep concern about inheriting these challenges.
“Aboriginal and Torres Strait Islander leaders are worried for their communities, who do bear the biggest burden of climate impacts in Australia while contributing the least to emissions.”
Dr Watfern said it was important to advocate for trauma-informed disaster responses from government, and preventive programs that build social connection and resilience for those communities on the frontline.
Allergies
The way allergies are impacted by climate change is two-fold, according to Macquarie University environmental health scientist Dr Paul Beggs.
“Perhaps the best example of this is allergic respiratory diseases such as hay fever and asthma,” he said.
“Increasing air temperature, and also increasing carbon dioxide concentrations, can influence airborne pollen in several ways, such as changing the timing and duration of the pollen season and increasing the amount of pollen plants produce.
“These changes can result in changes in when people experience symptoms and how severe those symptoms are.”
Dr Beggs said Australians in particular were highly vulnerable to adverse impacts of climate change on allergens.
“So many Australians have these diseases — over 10 per cent have asthma and almost 20 per cent have hay fever,” he said.
“Climate change is probably already impacting Australians with allergies.
“There is substantial evidence from other countries and regions that climate change has been impacting airborne pollen seasonality and concentrations for some time now, and similar research is slowly emerging in Australia.”
Overseas, the University of Utah School of Biological Sciences recently found nationwide pollen amounts increased by about 21 per cent between 1990 and 2018.
It also found pollen seasons were starting about 20 days earlier than in 1990.
“There continues to be a great need for government in Australia to look much more closely at the impact of climate change on allergies,” Dr Beggs said.
“However, one area where we do see government action is in response to thunderstorm asthma.
“This is particularly the case in Victoria, following the world’s largest, most catastrophic epidemic thunderstorm asthma event that took place there in 2016.
“But some other states and territories are also now starting to prepare for these rare events.
“Climate change and health is the issue of our times — the consequences of ignoring this are unfathomable.
“But the opportunities that come with responsibly addressing this issue will richly benefit us all.”
The World Health Organization is continuing to advocate for action on climate change.
“Many policies and individual measures, such as transport, food and energy use choices, have the potential to reduce greenhouse gas emissions and produce major health co-benefits, particularly by abating air pollution,” the organisation said.
The federal government released its National Health and Climate Strategy a year ago, detailing work it would do on:
