Since the 1980s, mosquito season has grown by up to 76% in many major US cities as a result of rising global temperatures and humidity. There are similar trends across the rest of the world. And with climate change accelerating, mosquito season is only forecast to get longer and longer. More mosquitoes buzzing around for longer isn’t just a source of annoyance. In many tropical and subtropical countries, mosquitoes carry and transmit vector-borne diseases (VBDs) like malaria, yellow fever, dengue, Lyme disease etc – which together result in more than 1 million deaths each year. Rising temperatures and humidity and a longer mosquito season mean more chance of VBDs affecting humans, and with increased migration (some of it a direct result of climate change), trade and travel, there is also an increased risk of VBDs spreading to the rest of the world. Read on to find out more about climate change and lengthening mosquito seasons.
Climate change induced by human activity is already a fact in many parts of the world. Global temperatures rose 1 degree Celsius over the source of the 20th century, and the 21st century has already seen more temperature records broken than at any time in recorded history. Each of the last three years has broken the record for global surface temperatures. Arctic sea ice is melting, sea levels are rising, climate refugees are on the move, and floods and extreme weather events are rising too. And things are only bound to get worse. In the absence of human action to reduce emissions of greenhouse gases, the Earth’s temperature could rise up to six degree Celsius by the end of the century.
With climate change forecast to continue, this is great news for mosquitoes and not so great news for the rest of us. You see, mosquitoes like other insects cannot regulate their own body temperature and rely on external heat sources to survive. If the temperature drops below a certain level, they cannot survive and thrive. Rising temperatures lengthen the warm season during which mosquitoes can breed and survive, and also increases their range geographically to regions further and further from the equator. Climate change is associated with increased humidity, rainfall, and flooding in some areas as well, and this is also a boon for mosquitoes as they require water as well as warm temperatures to breed; flooding and heavy rainfall will leave more and more sources of standing water lying around in which mosquitoes can lay their eggs. Moreover, the warmer weather and humidity will shorten the eggs’ incubation times, so that the mosquito population will rise in a very short amount of time.
As mentioned, this is not just a source of annoyance and irritation – although it is that as well. As we all know by experience, mosquitoes LOVE biting human skin, because our blood is a source of the protein they need to hatch their offspring. And the more mosquitoes there are breeding and laying eggs, the more we are going to be a source of food for them. But here’s the more frightening aspect of this. As we have seen, Mosquitoes carry disease, and the longer the mosquito season, the more chance there is for infectious disease to spread. Although VBDs overwhelmingly affect people in tropical and subtropical countries in the developing world, increased migration – including by refugees created directly by climate change – trade, and travel increases the chances of these diseases spreading to temperate regions where people have no immunity to them. Rising global temperatures and increased humidity, heavy rainfall and flooding, also allow mosquitoes to thrive in areas further from the equator. This is why, after the mass flooding that hit Louisiana in 2016, health officials prepared for an increase in the incidence of Zika and the West Nile virus infections – owing to the increased range of the Aedes mosquitoes created by the floods.
Indeed, according to the Intergovernmental Panel on Climate Change (IPCC), there is increasing evidence that particular disease vectors like dengue fever and West Nile virus are emerging in places they were previously absent from, and that this is due in part to climate change.
This is why we must become extra vigilant in protecting ourselves against mosquito bites, even if we live in a location where VBDs were hitherto unheard of (to find out what YOU can do to deter mosquitoes, please read some of our other articles). The world is rapidly changing – and not necessarily for the better!