A new study has predicted that climate change will result in millions more people, especially in Europe, being exposed to mosquito-borne diseases in the coming decades.
Two of the world's most dangerous mosquitoes – Aedes aegypti and Aedes albopictus – are known to thrive in hot climates, spreading viruses like dengue fever, yellow fever and zika more effectively between 26 and 29 degrees Celsius.
Mosquitoes currently threaten more than one billion people worldwide. But scientists say that as the world warms – the expected result of climate change – they will migrate to the poles, exposing millions more to the diseases they carry.
"We wanted to demonstrate how future projected climate changes would impact the risk of spreading vector-borne diseases – in this case, by two very tenacious global invaders," said Sadie J Ryan, associate professor of medical geography at the University of Florida. told Al Jazeera.
The researchers, whose study was published last week in the journal PLOS Neglected Tropical Diseases, have developed a model that has enabled them to keep up with changing climate-warming scenarios in the next century.
By doing so, they were able to find out where mosquitoes would probably migrate and the effect that the diseases they carry could have on people living in those regions.
"Over the next few decades, nearly half a billion people will be exposed," Ryan said. "By 2080, that number will rise to almost one billion in the worst of scenarios."
The researchers said that the threat to human health will likely also come from new and lesser known diseases transmitted by mosquitoes.
Before the zika epidemic in the Americas in 2015-2016 – which resulted in more than 600,000 reported cases and nearly 2,000 babies born with birth defects – the disease was poorly studied.
Researchers at the University of Florida have decided to include zika in their modeling, as well as chikungunya, a viral disease transmitted to humans by infected mosquitoes.
"This model advances the field, providing the first mechanistic prediction for the potential future risk of chikungunya and zika," Maria Diuk-Wasser, associate professor at Columbia University, told Al Jazeera.
Europe at risk
Researchers called the scale the potential risk of alarming, but the actual effect of mosquito movement only became apparent when it was mapped against human populations.
"Let's see the expansions of the pole, [into] some of the densest populations in Europe for the first time, leading to fairly rapid increases in new exposures, "said Ryan.
The team said its predictions were useful as a planning tool, giving decision-makers a better idea of the risks they would likely face and what they would need to do to monitor and control the spread of disease in the coming years.
"That means we can start thinking about how to allocate resources before surprising us with the next outbreak," Ryan said.
Added dimension to climate change
Last week, the United Nations weather agency reported that the extreme climate in 2018 affected 62 million people worldwide, forcing two million to move.
UN chief Antonio Guterres highlighted the rapidly expanding cost to public health of climate change, including hot flashes and flooding.
Researchers at the University of Florida expressed hope that their study will raise awareness of changes in health threats and the need to act to limit rising global temperatures.
"It gives us a sense of urgency to think about climate change mitigation in the context of global health," Ryan said.
"It shows us that places that we do not currently associate with tropical diseases will become areas of risk, but also that we can still mitigate this risk through actions on climate change."
A surprise found in the study was that as global temperatures rise, some areas that currently house the tiger mosquito (Aedes albopictus) will become too hot for them to thrive.
While this has a positive effect on human health in these regions – tropical zones in Africa and the Americas, Southeast Asia – scientists expressed concern about how temperature changes could affect whole ecosystems.
"The fact that we begin to see a declining risk for the Tiger mosquito indicates that we are facing a world that is too hot for mosquitoes to transmit disease, which in itself is an alarming sign," said Ryan.
"I was surprised to see the degree to which this would occur in certain areas," Diuk-Wasser said, adding that the non-linear effects of climate change on disease risk meant that "it poses a very difficult management challenge."
Ryan said more work needs to be done to better understand how the global temperature increase would affect humans, animals and plants.
"Understanding how they will respond to climate change will enable us to assess our future, plan management and control, and advocate climate mitigation strategies."