As our climate warms, so do our seas and soils, creating reservoirs of microbial life acting as deadly pathways for infection. Warming global temperatures promise new domains for bacterial, viral and fungal life forms which threaten to
jeopardise crop productivity and human health.
In 2015, the Paris Climate Agreement was set in motion; a goal to limit global warming to no more than 1.5°C above pre-industrial (pre-1850) temperatures. Earth is, however, already 1°C warmer than pre-industrial levels and will see this
1.5°C rise before 2040 ifno action is taken.
The Paris Climate Agreement Goal aims to limit global warming to no more than 1.5°C above the pre-industrial levels recorded 200 years ago. | Mika Baumeister / Unsplash
Increasing temperatures are changing vector-borne diseases
A warming climate poses both direct and indirect threats to human health, such as the spread of fatal diseases beyond their natural range. For example, malaria cases in Ethiopia and Colombia are shifting to higher, colder altitudes in
warmer years.
This shift is, in part, a result of how well mosquitos fare in warm conditions. It is, then, unsurprising that warmer temperatures give mosquitos a head start in survival, increasing their numbers even in areas that were once too cold for
them.
In addition to insects’ booming survival rates, warmer temperatures also give single-celled organisms called Plasmodium a better chance at survival. The bad news is that Plasmodium cells are malaria parasites, capable of
causing fatal illnesses. When a Plasmodium is not infecting a human host, it lives in the gut of an insect host, which is where mosquitos play their role.
‘A warming climate poses both direct and indirect threats to human health, such as the spread of fatal diseases beyond their natural range.’
So, it is no surprise that temperatures and malaria cases rise simultaneously, as both the vector and pathogen of malaria are well-suited to warm conditions. Until now, colder temperatures at higher altitudes in the tropics have slowed
Plasmodium development, reduced mosquito reproduction and even mitigated the biting rate of mosquitos, minimising malaria transmission.
Now, as temperatures are increasing worldwide, the once-too-cold higher altitudes have become habitable for infected mosquitos. The burden of malaria is now prevalent in highland areas across South America and Africa, with millions more
cases expected in these regions if mean temperatures increase by 1°C to 3°C. This surely highlights the importance of meeting the Paris Climate Agreement Goal of 1.5°C.
An increase of water-borne diseases in the Northern Hemisphere
Water-borne diseases are also expected to increase with global temperatures. Vibrio bacteria abundance,for example, shows a positive correlation with aquatic temperatures in the North Sea. Vibrio species cause a range
of illnesses, from ear infections to gastroenteritis, and even cholera.
‘Vibrio bacteria abundance, for example, shows a positive correlation with aquatic temperatures in the North Sea.’
With frequent storm surges and floods predicted in future years, human populations are likely to be regularly exposed to Vibrio cells, making populations susceptible to disease outbreaks.
Thawing permafrost may uncover dangerous pathogens
Even in the coldest places on earth, such as the Arctic, human diseases are emerging as a result of global warming.
The frozen ground in the Arctic, known as permafrost, acts as a frozen safe, locking away pathogens in the freezing temperatures. Now, with the Arctic warming twice as fast as the rest of the globe, the permafrost is melting and releasing
the once imprisoned pathogens.
This melting permafrost is also unearthing many long-dead corpses of both humans and animals, along with the disease that killed them. In 2016, a 75-year-old reindeer carcass emerged from the frozen ground, releasing Bacillius anthracis
bacteria which hospitalised over 100 nomadic Nenets people with anthrax and killed a 12-year old boy. Elsewhere in the Arctic, the corpses of smallpox victims from over 100 years ago are resurfacing as the once-frozen ground shifts and
melts.
Fusarium fungi cause plants to wilt and xylem necrosis, as seen in this banana plant. | Scot Nelson / Flickr
In the face of climate change, it is easy to focus on how it directly affects populations, but its indirect effects can be just as destructive.
New soil-borne pathogens will affect the plants we eat
It is not just humanpathogens becoming more abundant in our warming world; plant pathogens are more abundant than ever. It is easy to think that plant pathogens are less of a threat to humans, after all, they are not infecting us!
But an increase in plant diseases means fewer crops, less food, fewer textiles, less livestock and less medicine.
A nine-year global field experiment shows that soil-borne fungal plant pathogens are increasing with temperature. The study evaluates the effects of 2°C warming on ecosystem characteristics in over 200 ecosystems across six continents.
‘It is not just human pathogens becoming more abundant in our warming world; plant pathogens are more abundant than ever.’
A paper published in 2020, states that ‘many of the most aggressive plant pathogens are soil-borne fungi’. These include
Alternaria alternata, capable of infecting over 380 plant species,and Fusarium oxysporum,one of
the world’s most economically destructive plant pathogens.
The study found that Fusarium oxysporum abundance tripled with an increase of 2°C, while Alternaria alternata abundance increased sevenfold. What is more, there is not yet a reliable protocol for identifying and controlling
diseases caused by Alternaria alternata, highlighting the risk it poses to food security worldwide.
Approximately 15% of crops are lost to biological threats, a figure that is only increasing as the climate warms. | Red Zeppelin / Flickr
If global temperatures increase by 2 °C or more, both pathogens are likely to be detrimental to the future productivity of important plants such as wheat, sunflower, cabbage, tomato and potato, as well as medicinal plants like hibiscus and
aloe vera.
Plant pathogens also pose a threat to wild plants and ecosystems, which provide services and livelihoods for billions of people. Soils from natural ecosystems may act as reservoirs of infection for crops,and indeed vice versa.
‘Soils from natural ecosystems may act as reservoirs of infection for crops and indeed vice versa.’
If the Paris Climate Agreement Goal of 1.5°C is not met, the productivity of plant communities worldwide, along with food security, may be jeopardised. Reaching the Paris Climate Agreement Goal will require immediate and dramatic reductions
in greenhouse gas emissions via changes in land use, energy production and consumption and industrial systems.
Should greenhouse gases continue to rise at their current rate, we could be faced with a 4-5°C rise by 2100, a rise which will certainly bring unprecedented exposure to diseases for both human and plant populations.
Featured image: Oregon State University / Flickr
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