Climate change is already forcing millions of people to migrate – and it will only get worse
Scientists now believe that as well as profound effects on societies, economies and geopolitics, these climate-driven human migrations could also change the spread and occurrence of infectious disease outbreaks. Researchers have already begun to warn how changes in temperature and rain patterns might shift the spread of disease, for example, as carriers like mosquitoes roam further afield.
An extra 4.7 billion people might be at risk of malaria or dengue by 2070 as the “epidemic belt” of the diseases expands according to one recent study. A 2022 systematic review found that more than half of known infectious diseases will be aggravated by climate hazards. Scientists are also now starting to look specifically at how human migrations caused by climate change, might alter the spread and distribution of disease.
In a recent paper in the journal Nature Climate Change researchers set out the ways that climate change migrations might foster disease outbreaks. The paper concludes: “With climate change and climate disasters affecting populations at an increasingly alarming rate, the sudden displacements and long-term migrations that they cause could have devastating consequences for the distribution and burden of infectious diseases.”
One of the authors, Dr Houriiyah Tegally, of the Centre for Epidemic Response and Innovation at Stellenbosch University, who is starting a three year study of the issue, said: “We make the case that the mechanisms of climate related migration to infectious diseases make sense and there’s a lot of migration that is due to climate disasters, or climate change.
“But currently there’s not this proper link to confirm the increase in diseases because of climate migrations and that’s the goal of our funded research.”
Movement of viruses linked to movement of people
Major human movements throughout history have been credited with spreading infectious diseases. From plagues spread by armies in antiquity, to European colonists taking measles and small pox to the New World, migrations have long been known to spread diseases and lead to new outbreaks.
The phenomenon has come under the spotlight with increased human mobility, as newer infections like SARS and Covid-19 have spread rapidly through international air travel.
Dr Tegally has previously done work on how human mobility affects the dispersal of viruses, reconstructing how Covid spread around the world. She said: “The movement of viruses is very much linked to the movement of people. It’s people that carry viruses.”
Her three-year project will try to match genomic surveillance data of viruses like dengue and chikungunya with satellite tracking of large population migrations. She added: “The more genomic surveillance we do, the more we can reconstruct the transmission dynamics and therefore link to underlying people movement or climate change.”
Scientists predict two different types of climate migration in the future, set off by what they call ‘fast’ and ‘slow’ onset events. Fast-onset climate disasters such as cyclones, heat waves, and forest fires occur over a short time frame. People move as their homes are destroyed, and their livelihoods are lost. They often go to cities or camps temporarily, but aim to return once the destruction is over.
So-called slow-onset climate events, such as increases in sea level, coastal erosion, desertification and rising temperatures, happen over longer time frames and lead to slower movement. For example in rural Pakistan, as temperatures have risen and income from agriculture has dropped, there has been a long term migration away from the land.