China’s remarkable recent surge in agricultural output is at risk from climate change. However, how much risk won’t be clear without better regional climate predictions and understanding of how crops will react to their altered environment. That’s according to Peking University’s Shilong Piao and his colleagues. “Climate simulations point to serious potential vulnerabilities in China’s future agricultural security,” they wrote in top journal Nature on Thursday, “but extensive uncertainties prevent a definitive conclusion.”
In part those uncertainties come from Chinese farming’s success over the past four decades, increasing rice, maize and wheat yields by 90, 150 and 240 percent respectively. These improvements are vital as the country has just 7 percent of the world’s arable farmland available to feed 22 percent of the world’s population. However, they also obscure the impact of more frequent heat-waves, retreating glaciers and an average 1.2ºC temperature rise in China since 1960. “The improvements of crop management have been so important that they prevent a clear conclusion on the net impact of historical climate change on agriculture,” the team writes.
Scientific uncertainty in several other areas adds to this masking. For example, scientists disagree on how plants respond to the raised levels of greenhouse gas CO2 humans are pumping into this atmosphere. Some predictions suggest that “CO2 fertilization” will increase the productivity of rice and wheat crops still further, but others do not. And while warming has extended the length of the potential growing season for crops, allowing earlier planting, later harvesting, and northward expansion of rice farming, it also attracts unwelcome visitors. “Unfortunately, pests and diseases may also expand their geographic ranges as the climate warms, increasing stress on crops,” the researchers observe.
Water availability will be crucial, as Shilong Piao points out that that China’s water resources per person are just one quarter of the world average and that regular severe droughts have hit the country over the past six decades. Climate change means that most of China has experienced a decrease in the annual number of rain days. It also means that the glaciers in China’s mountains are melting, providing it with more “runoff” water now, but creating problems for the future.
“Several studies converge on the conclusion that glacier melt runoff may peak during 2030–2050, and could gradually decline afterwards,” Shilong Piao and his colleagues write. “Even though the exact timing and magnitude of the ‘tipping point’ of each glacier is still uncertain, the projected long-term exhaustion of glacial water supply should have a considerable impact on the availability of water for both agricultural and human consumption. We expect that such a critical issue would prompt a complete redesign of water management systems for the vast areas of western China.”
“In the ‘best case’, crop production in China will not diminish in response to climate change, thanks to species and practice adaptation and to CO2 fertilization,” the team concludes. However they also consider a worst case scenario, where CO2 provides no benefit, and glacial water supplies fall while extreme weather events, ozone pollution, pests and disease become more common. “Such a scenario would have quite adverse implications for food security,” the scientists write. “We might see decreasing crop productivity by 3–22 percent for wheat, 8–18 percent for rice, and 9–30 percent for maize over the next decades.”
While the decline in total emissions is good news, Gunnar Myrhe from Norway’s Center for International Climate and Environmental Research and his colleagues note that the fall is lower than previous estimates. “Despite this recent decline, fossil fuel CO2 emissions are now almost 40% higher than in 1990 and above most IPCC [Intergovernmental Panel on Climate Change] projections,” they wrote in Environmental Research Letters.