The consensus among scientists is that we are in an era of global heating and extreme weather events, primarily due to the devastating effects of human action on the environment. Why are researchers concerned, and what are the implications for health?
The Lancet Countdown team is a group of over 120 leading experts on climate, public health, economy, and political science — among others — who have committed to monitoring climate change, particularly its impact on global health.
Since 2015, the year of the Paris Agreement, the experts affiliated with the Lancet Countdown commission have published yearly reports assessing this situation and keeping signatory governments and decision-makers accountable for the commitments they have taken on following the Agreement.
The latest report, which appeared in The Lancet in October 2021, records “deepening inequities” across all regions as global heating remains a concern. The report discusses the impact of climate change in the context of the COVID-19 pandemic, and it emphasizes the concern caused by extreme heat events and related natural disasters that have occurred over the past 2 years.
Among the issues outlined in the Lancet Countdown report 2021, there is the impact of climate change on the livelihood of communities around the world, its direct and indirect effect on mental and physical health, and the way in which it contributes to the spread of infectious diseases.
These findings largely coincide with those outlined by another set of landmark reports on climate change — those of the Intergovernmental Panel on Climate Change (IPCC).
According to the IPCC 2022 reports, at present, extreme weather events caused by human action are surpassing the resilience of some ecological and human systems, sometimes with irreversible effects.
The reports show that weather extremes related to climate change have affected the productivity of various food sectors — including agricultural, forestry, and fishery sectors — around the world, thus exacerbating food insecurity.
They also emphasize the impact of climate change on mental health, and the ways in which it contributes to the spread of vector-borne communicable diseases.
In our latest installment of the In Conversation podcast, we discuss these aspects at length with two key experts. One of them is Prof. David Pencheon, honorary professor of health and sustainable development at the University of Exeter in the United Kingdom, and founder of the Sustainable Development Unit for National Health Services England and Public Health England.
Our other interviewee is Dr. Marina Romanello, a research fellow at the University College London Institute for Global Health, research director of the Lancet Countdown on Health and Climate Change, and one of the co-authors of the latest Lancet Countdown reports.
You can listen to our podcast in full below, or on your preferred streaming platform.
According to the Lancet Countdown report 2021, “[t]he world is now 1.2 [degrees Celsius] warmer than in the pre-industrial period (1850–1900),” with the past few years recorded as the hottest yet — 2016 has seen the highest levels of heat around the world.
The IPCC reports 2022 record the current global heat level as even higher, placing it at 1.5 degrees Celsius (34.7 degrees Fahrenheit) hotter compared with the pre-industrial period.
According to data from the National Aeronautics and Space Administration (NASA), most of the global heating has occurred abruptly over the past 40 years as a result of human activity that has led to an increase in greenhouse gas levels.
“[G]reenhouse gases that have been accumulating in the atmosphere due to human activity are gases like carbon dioxide [and] methane. And what these gases do is [that they] basically absorb the heat, and they don’t allow heat that comes from the Sun into the Earth [to] be reflected back into space,” Dr. Romanello explained.
“So what happens [as a result] is that, as heat from the Sun reaches the Earth, they act like a blanket, they trap the heat inside the Earth’s atmosphere, and that makes the temperatures go up. And that is part of what climate change is, because that generates cascading effects in terms of increasing [the] temperatures of the water. That alters hydrological cycles and generates other impacts on the climate [and] on our environment that add to the whole combo that we call ‘climate change’.”
– Dr. Marina Romanello
But what does this mean for health? For one, climate change puts in motion a complex “domino effect” that ultimately impacts people’s livelihoods, their access to food security, and to clean water, all of which are crucial to human health.
One example is that of melting glaciers. Research published in Nature in 2021 confirms that glaciers, melting due to the steady rise in global temperatures, have driven approximately 21% of the rise in sea levels over the previous 20 years.
Global heating also leads to marine heatwaves, which in conjunction with the rise in sea levels impact marine ecosystems. Such effects can alter fishing practices and reduce the availability of marine resources for coastal communities.
Moreover, rising sea levels also increase the risk of catastrophic floods that endanger the lives of those residing in coastal areas.
The IPCC reports 2022 also emphasize the ways in which global heating has impacted agricultural productivity over the past 50 years, particularly in low- and middle-income countries, which were already struggling with food insecurity. According to IPCC data:
“Crop yields are compromised by surface ozone. Methane emissions have negatively impacted crop yields by increasing temperatures and surface ozone concentrations. Warming is negatively affecting crop and grassland quality and harvest stability. Warmer and drier conditions have increased tree mortality and forest disturbances in many temperate and boreal biomes, negatively impacting provisioning services.”
Dr. Marinello also stressed the impact of climate change on water and food security, noting that the people who are likely to be most affected are those who are already facing these issues in the first place.
“I think that one of the things that we get more worried about when we think about climate change is precisely food and water insecurity, especially because the most vulnerable in the world are at such increased level of risk from climate change that [it] adds on top of their already pretty frail food and water systems,” she told us.
“We’re seeing, on the one hand, changed precipitation patterns with increased floodings, increased droughts in different areas, we see extreme weather events that also lead to crop failure, […] all of that undermining not only crop productivity, but also crop supply chains and food supply chains,” she noted.
“And on the other hand, with the extreme heat exposure, we’re already seeing that that starts undermining crop productivity directly as well by changing the maturation times of different crops. So that also is posing limits on […] food productivity,” stressed Dr. Romanello.
But climate change, particularly extreme heat and extreme weather events, can have a more direct impact on the human body, sometimes in surprising ways.
A recent study from the Karolinska Institute in Sweden showed that more and more people are getting hospitalized with hyponatremia — abnormally low sodium levels — due to high outdoor temperatures.
“Oversimplified, hyponatremia can be the result of sodium deficiency (low intake or high losses) or excess water,” study co-author Dr. Jakob Skov told Medical News Today.
“[T]here are two plausible explanations for heat-related hyponatremia — salt loss from sweating resulting in a sodium deficit or excessive hydration due to an exaggerated fear of dehydration,” he explained.
There is also some evidence that temperature variations might influence the way in which the immune system reacts to pathogens, such as viruses. For example, a study that appeared in PNAS in 2019 looked at how efficiently the immune systems of mice reacted to influenza viruses under different temperature conditions.
The researchers found that mice that they had exposed to high ambient temperatures — of 36 degrees Celsius (96.8 degrees Fahrenheit) — had a dampened immune response to the influenza virus.
Moreover, as Prof. Pencheon and Dr. Romanello told us, heating and sudden temperature variations are also linked to other health risks. One unexpected effect might be on digestive health, as Dr. Romanello observed.
“[E]xtreme heat exposure [increases] the permeability of the digestive barriers, and therefore […] the susceptibility […] [to] infections through the digestive system,” she told us.
She also noted that “there’s a link between heat exposure and kidney disease, particularly in outdoor workers, in people working in the fields.”
“And there’s also some evidence of neurological disease being exacerbated by extreme heat exposure, like for example, [in] people that have seizures or other neurological problems,” she added.
One systematic review from August 2021 indeed showed that there was a link between increasing ambient temperatures and a worsening of symptoms of neurological conditions, from Alzheimer’s disease and Parkinson’s to epilepsy and migraine.
The review analyzed no fewer than 84 studies looking at climate change and neurological health, and it concluded that global heating may indeed contribute to worsening symptoms, a higher number of hospitalizations, and a higher risk of death related to these conditions.
Another particularly concerning issue in the context of the COVID-19 pandemic is the effect that climate change has on the spread of infectious diseases.
The Lancet Countdown 2021 report emphasizes that “the changing environmental conditions are also increasing the suitability for the transmission of many water-borne, air-borne, food-borne, and vector-borne pathogens,” undermining the efforts of medical scientists and public health organizations to mitigate this threat.
According to the Lancet Countdown report, some of the diseases whose transmissibility has increased due to climate change-related factors include malaria and diseases caused by arboviruses like dengue, Zika, and chikungunya. All these are vector-borne diseases.
Research has shown that climate change affects the environment where pathogen-carrying vectors — such as insects, particularly mosquitoes — live, impacting their migration and life cycle patterns. This can lead to the vectors carrying pathogens to different regions than the ones they initially inhabited, for example.
Climate change can also influence how long pathogen-carrying vectors survive, and it can impact the incubation period of certain viruses through temperature fluctuations.
“One of the most cited examples of how infectious diseases are changing [is] in so-called arthropod-borne diseases. These are diseases that are spread by insects [like] mosquitoes […], and of course, a lot of these insects are exquisitely sensitive to which ecosystems they can survive in,” Prof. Pencheon told us.
Because of this, he explained, malaria and other transmissible disease are spreading faster and farther around the world.
There are fears that, even as we are still navigating the COVID-19 pandemic, more epidemics — or even other pandemics — may soon arise, and climate change will, at least in part, be to blame.
In November 2021, Australian Academy of Science Fellow Prof. Edward Holmes expressed his worry that climate change will be responsible for the next pandemic:
“[Pandemics are] going to happen more and a key driver of this is climate change. As climates change animals will change their distribution; they’ll probably group together more allowing viruses to jump more easily between them. With more humans living closer to wildlife, this opens the gate for potentially deadly viruses to then jump to human hosts.”
It is increasingly clear that human health and the health of our global environments are crucially interconnected, and that we cannot have one without the other.
Yet, the Lancet Commission 2021 report found governments and decision-makers lacking in their efforts to stop climate change and mitigate its negative impacts.
“Governments with the fiscal capacity have responded to the COVID-19 pandemic with massive spending packages, to cushion the impacts of the crisis and start to bring about economic recovery. But […] the response to climate change, and commensurate investment, remains inadequate,” it concludes.
“With government leaders more engaged with the health dimensions of climate change than ever before, countries across the globe should pursue low-carbon economic recovery pathways, implementing policies that reduce inequities and improve human health,” its authors advise.
And there are also smaller-scale steps that organizations and health services can take to pull their weight in terms of becoming more eco-friendly, according to Prof. Pencheon and Dr. Romanello.
“One of the things [health systems should do] is to realize that health systems are big medical-industrial complexes, and they are themselves part of the problem. Health services are essentially rescue services, […] really. So we’ve got to get our own house in order,” said Prof. Pencheon.
According to him, health services could help set the tone in terms of how we address the climate crisis, and how we understand its effect on public health.
“[I] f we treat climate change as a health issue, and not just as an environmental issue, it makes it much more immediate to everybody.”
– Prof. David Pencheon
Dr. Romanello agreed. “It is fundamentally a health crisis that we have [on] our hands,” she emphasized, explaining that “much of what we talk about when we talk about climate change action [and] climate change mitigation has to do with healthier lifestyles, with reducing the burden of disease through more physical activity, through healthier, more plant-based diets, through reduced exposure to air pollution and other environmental determinants that damage our health.”
“[B]y increasing communication from the health system, by promoting healthier lifestyles, we on the one hand promote behavior shifts that determine low-carbon transitions and facilitate those low-carbon transitions. And on the other hand, we reduce the burden of disease, we reduce the pressure on the NHS, we reduce the carbon footprint that comes from the health systems which we saw during the [COVID-19] pandemic […] [It] is fundamental that we do shift our attention towards what we need to be doing to protect our health, to deliver those healthcare benefits, and to deliver healthier futures as well.”
– Dr. Marina Romanello