Better green than red

Better green than red
July 1, 2000

In literally hundreds of experiments conducted around the world, the major food crops of China have been shown to produce substantial improvements in yield and water use efficiency thanks to elevated levels of atmospheric carbon dioxide (CO2).

Gloom-and-doomers quickly point out that these experiments seldom take into account changes in future climate that could ruin all the good news from the biological literature.

Their arguments are bolstered by several facts including a) Some climate models predict that China will have more drought-like conditions in the future due to greenhouse-induced changes in regional climate and b) China’s reliance on highly water-consuming rice crops makes it especially vulnerable to climate change.

Throw in the world's largest population, and you might conclude we have another possible emerging food crisis on our hands.

If that has occurred to you, relax! The crisis was over before it had even begun. An agroclimatologist at Germany’s Johannes Gutenberg University decided to examine long-term trends in evapotranspiration and precipitation in China and their combined effects on surface hydrology, soil moisture, and resultant crop yields. Thomas was able to assemble climate data for 65 stations across China for a 40-year period extending from 1954 to 1993. He then calculated an array of evapotranspiration, soil moisture, and yield estimates.

The news from his analyses, as reported in a recent issue of Agricultural and Forest Meteorology, was nothing short of glorious. Thomas found that for China as a whole, the yield index had increased by 4.5 percent over the past 40 years, while the soil water deficit had decreased by 13.9 percent. The yield index had maximum trends up to 23.5 percent in East China, with lesser increases along the South Chinese coast.

Thomas concludes:

“Results presented here indicate that the water supply situation has generally improved over the last 40 years, particularly in the important agricultural centers of East and South China.

“Yield index rates, on average at about 70 percent to 80 percent, have increased by 5 percent to 10 percent. Irrigation demand (as determined by the soil water deficit) has decreased by more than 100 to 200 mm in this region.”

Near the end of Thomas’ paper, he notes:

“Regional climatic change appears to have had a beneficial effect for several regions in China that have to cope with an increased demand on water resources by a growing population and industry as well as an intensified agriculture.”

Of course, what has happened in the past 40 years is not necessarily a guide to what will happen in China over the next 40 years.

But if we look at the facts we find overwhelming evidence that increased atmospheric CO2 concentrations will be beneficial to yields of China's most important crops.

Further, given the recent analyses by Thomas, we find that the regional climate of China is showing no signs of deteriorating into an unfavorable state. In fact, the climate of China seems to have improved in many ways over the period of historical records.

China’s agricultural future looks greener every day.


Reference

Thomas, A., 2000. Climate changes in yield index and soil water deficit trends in China. Agricultural and Forest Meteorology, 102, 71-81.