The amount of farmland hit by crop pests and diseases in China has quadrupled in the past 50 years, according to a recent study. Climate change was found to be responsible for more than a fifth of this change – an ominous warning for the agricultural industry in a warming world.
China is the world’s largest producer of rice and wheat and the second largest producer of maize. A rapidly warming planet, however, could threaten the future of the food supply needed by its population – which is roughly a fifth of the world’s population – due to rising crop pest and disease outbreaks.
“I read a few surveys a few years ago. When they asked farmers their perception of climate change, the first item coming out is that they are feeling a change in crop pests and diseases,” says Xuhui Wang, an assistant professor at Peking University and an author of the report. “This aspect, however, is largely dismissed in the literature, and the understanding of the relationship between crop pest and disease occurrence and climate variability is largely uncertain. So our knowledge of this is pretty limited.”
Using a database of more than 5,500 statistical records dating back to 1970, the researchers calculated that the total proportion of cropland suffering from pest or disease outbreaks shot up from 53 percent in 1970 to 218 percent in 2016. A single area can suffer from pest or disease outbreaks multiple times in a year, so this number can exceed 100 percent. (In other words, if these outbreaks were to theoretically affect all Chinese farmland equally, every hectare of land would have been invaded by pests or diseases more than twice in 2016.)
This figure doubles to 460 percent by the end of the century under the worst-case climate scenario envisioned by the Intergovernmental Panel on Climate Change (IPCC), in which the planet warms by roughly 4.4 degrees Celsius from pre-Industrial levels. Such a future would see a nearly 3 percent year-on-year increase in the amount of land affected by crop pest and disease outbreaks.
The UN Food and Agriculture Organization (FAO) estimates that up to 40 percent of the world’s crops are destroyed by pests annually and, along with plant diseases, drain hundreds of billions of dollars from the global economy – and climate change is making the problem worse. Shifting weather patterns are affecting the ranges, lifecycles and other survival factors of pests.
The fall armyworm, for example, is now found in more than 70 countries across the Americas, Africa and Asia, and annually causes almost USD 10 billion in maize losses within Africa alone. Its range has expanded within warmer climates and may spread to suitable areas in southern Europe. The fall armyworm eats the stems and leaves of a wide variety of plants, and in China the pest infested 1.13 million hectares of land within 26 provinces in 2019.
Coffee leaf rust, a fungus now found across the world that disrupts coffee plants’ ability to photosynthesize, is another example of a threat to crops; climate change makes the fungus more infectious and shortens its incubation period. Potential links have been made between outbreaks of coffee leaf rust in Central America and surging northward migration flows of regional inhabitants.
Wang’s study stated that the most prevalent pests in China were Lepidoptera, the order that includes moths and butterflies (and the fall armyworm), which accounted for more than a third of the affected cropland. This was followed by Homoptera, which include aphids, cicadas and leafhoppers. Fungi were the most prevalent type of disease.
Three temperature-related factors were found to be linked with rising outbreaks: maximum daily temperature, minimum daily temperature and the number of days with frost. The authors hypothesized that the connection between pest outbreaks and the minimum temperature could be due to many of the pests being nocturnal, and that the warmer nighttime temperatures could spur their activity. Fewer days out of the year in which temperatures dip beneath the freezing point could also allow more pests to survive the winter and proliferate.
All Chinese provinces have undergone a rise in such outbreaks, but some have more than others. The two major breadbasket regions of China, the North China Plains and middle-lower Yangtze Plains, have been the most impacted by pests and diseases overall. However, compared with other factors that could increase outbreaks such as farming practices, climate change has had the greatest influence on the growth of crop pests and diseases in the northern and western provinces of Jilin, Inner Mongolia and Xinjiang. Under the IPCC’s worst climate scenario, outbreaks in Qinghai and Shaanxi provinces are projected to increase the most by the end of the century.
In spring 2020, the Chinese government laid out regulations for preventing and controlling agricultural pests and diseases, including the establishment of a national system for monitoring outbreaks. Beyond China, however, crop pests and diseases have increased their global range since the 1950s, and a number of important crop-producing countries could become invaded by all of their potential pest and disease threats by the middle of this century.
Wang said that global information on crop pest and disease trends are generally lacking, and thus drawing exact conclusions about their effects on global food security remains difficult. Nevertheless, he noted that international collaboration is needed to tackle the spread of outbreaks. “Crop pests do not have national boundaries,” he said.
“The consequences of climate change are not only through a warmer climate alone. It’s through the interconnection of the entire biosphere that is threatening or…exposing our food security to increasing risks.”