A biblical explosion of mice has been ravaging Australia’s southern and eastern agricultural regions in recent months. New South Wales Farmers, an agricultural association, estimates that damage to crops will reach AU$1 billion.
Conditions for the plague are strongly linked to climate change, particularly the successive, intense droughts that culminated in the Australian wildfires of 2019–2020 and the heavy rainfall that followed. This shift led to bumper crop yields, helped along by struggling farmers who sowed more than 23 million hectares of land to compensate for wildfire losses. Steven Belmain, an ecologist and agricultural pest expert at the Natural Resources Institute at the University of Greenwich attributes much of the plague to this confluence of climate-related and agricultural factors: ‘Usually, you’d have a dry season with minimal vegetation which would collapse the rodent population. But this year, rains have continued into the following season.’
More than 60 known diseases are transmitted by rodents. ‘We’re most concerned that the perfect environment for disease emergence is being created because of the interactions of abnormal weather patterns, rodent outbreaks and the spread of diseases like leptospirosis, bubonic plague and lassa fever,’ says Belmain. Many rodent-transmitted diseases are becoming more resistant to available treatments. Madagascar, for example, has seen outbreaks of rodent-transmitted, antibiotic-resistant plague in recent years, which have since been successfully controlled. ‘However, control gets harder when rodent populations have these huge boom and bust cycles of population growth that we’re seeing in many parts of the world now,’ says Belmain.
Rodent outbreaks are not the only concern. Increased numbers of cyclones create good conditions for insect-pest outbreaks. In May 2018, an unusually powerful cyclone, Mekunu, made landfall over the Arabian Peninsula before crossing over Oman, bringing heavy rainfall all the way to Saudi Arabia. The warm, sandy and wet soils were the perfect conditions for desert locusts to hatch. Usually after wet periods, dry conditions kill off locusts, but cyclone Luban followed in October 2018. Then, at the end of 2019, yet another, Pawan, carried the locusts across to East Africa, where they entered the ‘gregarious’ phase of their life cycle, causing huge crop damages in East Africa. ‘Such events are likely to increase in the future,’ wrote the authors a 2020 commentary on the East African desert locust plague, published in Nature Climate Change. ‘The increased cyclone frequency and more extreme climate variability could increase the likelihood of pest outbreaks and spread, adding compromised food security to the consequences of storms themselves.’
To many, these events highlight that climate change is not simply a phenomenon that ends with higher annual temperatures and extreme weather; the consequences ripple outward, and are felt most acutely by nations wrestling with political instability, poor governance and limited financial resource. But pest outbreaks could also catch richer countries off guard. ‘There’s a real issue of prediction and resource allocation coming as pests move around the world,’ Belmain says. Research shows that since 1960, crop pests and vector-borne diseases have been moving at three kilometres per year towards the Earth’s poles as temperatures rise. That is likely to bring novel pests and their associated diseases to areas currently without established control operations. ‘Hantavirus and Congo hemorrhagic fever, for example, are moving upwards towards the UK with climate change,’ says Belmain. Just another of the things we can look forward to with a warming climate.