Climate change is also likely to lower wheat production:  Global warming will have a bad effect on heat-sensitive wheat, slashing yields even more than was originally feared.  It could be much harder than we thought to feed everyone in a warmer world. Hot spells are cutting wheat yields in northern India, and models of global warming’s effect on crops may have underestimated the problem by a huge amount…an average warming of 2 °C may [cause losses] 50% greater than thought (Nature Climate Change, DOI: 10.1038/nclimate1356).  Earlier studies suggested that, by 2050, warming could cut wheat yields by 30 per cent in places like India – a figure that may now be optimistic. Yet global yields need to rise 50 per cent by then to feed the world’s growing population (Feb 3, 2012.  Extreme heat ages vital crop. New Scientist.)

Christina Larson.    February 8, 2013. Losing Arable Land, China Faces Stark Choice: Adapt or Go Hungry.  Science (339): 644-645

For half a century, Chinese scientists have been flocking to this spot on the eastern rim of the North China Plain, China’s breadbasket, to probe pressing agricultural questions. The region just north of the Yellow River is ground zero for tackling food-security challenges such as flood control, drought, wind erosion, and soil alkalinity. To this list of concerns, researchers have now added climate change and its potential impact on grain yields.

Across the globe, scientists and policy-makers are studying how climate change will affect agriculture. But in China, the question is especially urgent. The country has roughly 20% of the world’s population but only 7% of its arable land—a share that is shrinking in the face of rapid urbanization. From 1998 to 2006, more than 860,000 hectares of arable land were swallowed up by cities each year on average, according to data from China’s Ministry of Land and Resources.

Changing dietary habits, meanwhile, are fueling a rapid rise in food consumption. Accompanying the expansion of China’s middle class is a growing appetite for meat, which heaps more pressure on land and water resources. In 1978, China’s total meat consumption was 8 million tons, but by 2012 it had ballooned to 71 million tons, according to the Earth Policy Institute, a think tank in Washington, D.C. In 2011, one-third of China’s total grain harvest was converted to feed for livestock and aquaculture.

Climate change could exacerbate the fallout. According to the Chinese government’s Second National Assessment Report on Climate Change in 2011, rising sea levels are likely to threaten China’s eastern rice-growing regions by 2050, about the time that eight provinces in the north expect to face severe water shortages.

Already, annual mean temperatures near Yucheng rose 0.8°C between 1955 and 2011, according to China Meteorological Administration (CMA) records. The uptick is felt most in winter and spring—coinciding with the growing season for winter wheat, the region’s most important staple crop.

Contrary to conventional wisdom, rising temperatures in China’s heartland are translating into shorter overall growing periods. Although warming accelerates the early stages of wheat growth, the length of the reproductive period—the phase spanning flowering and maturity—remains roughly the same for cultivars now commonly grown in the region. Faster growth may mean fewer grains, spelling lower yields.

By comparing records compiled by CMA and provincial agricultural departments between 1980 and 2008, Tao has attempted to tease out the climate signal from other factors affecting yield, such as crop management and fertilizer use. In a paper published online last October in Climate Research, Tao linked changes across China in temperature, precipitation, and solar radiation over those 3 decades with 1.3% and 1.7% reductions in projected wheat and maize yields, respectively. That translates to hundreds of thousands of tons of lost harvest. A team at the Chinese Academy of Agricultural Sciences in Beijing and the International Food Policy Research Institute in Washington, D.C., has also identified a significant impact from climate change. They reported in Agricultural and Forest Meteorology in 2009 that warming caused a 4.5% decline in growth of wheat yields across China from 1979 to 2000.

Regional variation complicates the picture. In frigid northern China, where annual mean temperatures have risen faster than the national average, warming has extended arable land northward. But the potential agricultural benefits may be hard to reap, Tao warns, as climate change is expected to increase the frequency of drought and extreme weather events in an already water-stressed region.

Much of northern China is dry, making agriculture dependent upon irrigation from the Yellow River and the northern China aquifer. But pollution has degraded the quality of China’s “Mother River” and growing cities are siphoning off water for urban uses. Some 120 billion cubic meters more water were pumped from the aquifer than were replaced by rainfall over the last 4 decades, resulting in a steadily retreating water table (Science, 18 June 2010, p. 1462).