How does rising atmospheric CO2 affect marine organisms?

Click to locate material archived on our website by topic

Global Warming and World Food Security

Paper Reviewed
Liu, H., Ge, Q., Zheng, J., Hao, Z. and Zhang, X. 2014. Crop yield and temperature changes in North China during 601-900 AD. Advances in Meteorology 2014: 10.1155/2014/137803.

In a recent study to come out of China, Liu et al. (2014) write that "food security under the changing climate is a great challenge for the world," noting that it has been stated by Porter et al. (2014) in the IPCC's Fifth Assessment Report that "the negative impact of global climate warming on crop yield is more common than the positive impact according to the data from the past fifty years." However, Liu et al. report that studies based on historical data for the past several centuries suggest just the opposite, i.e. that "climate warming is good for crop harvests while climate cooling is bad for crop harvests in the world's main crop production areas such as Europe (Braudel, 1992; Parker and Smith, 1997; Holopainen and Helama, 2009; Zhang et al., 2011) and China (Zhang, 1996; Ge, 2010; Su et al., 2014) in the temperate region." And these observations lead them to conclude that "the current lengths of studies used to evaluate climate impacts on agriculture are too short to detect long-term trends," which they thus go on to demonstrate.

In making the case for their conclusion, the five Chinese scientists employed proxy data-based climate reconstructions that indicate that the Sui dynasty (581-618 AD) and Tang dynasty (618-907 AD) had warm climates comparable with the present, citing in this regard the study of Ge et al. (2003). And they additionally note that within this primarily warm climate regime, there were imbedded temperature variations - with cooling segments of inter-annual, multiple-decade and century-scale magnitude - which enabled them to assess crop yield responses to both heating and cooling from information provided about food availability in numerous historical documents that have been brought together in several historical compilations that deal with various aspects of China's past, including Wang (1955), Wei et al. (1973), Li (1974), Liu (1975), Ouyang et al. (1975), Sima (1975), Dong (1985), Wang et al. (1985) and Song (2008). And what did they thereby discover?

As indicated in the figure below, "on the one hand," as Liu et al. describe it, "a declining trend of crop yield co-occurred with the climate cooling trend from 601 to 900 AD" (Figure 1a), while on the other hand, they indicate that crop yields were positively correlated with 30-year periods of warming (Figure 1b).

Figure 1. (a) Reconstructed Central East China temperatures (relative to the mean of 1951-1980) and 30-year regional mean crop yields over the period 601-900 AD, (b) the correlation between crop yield and temperature. Adapted from Liu et al. (2014).

And based on these real-world observations recorded in the historical documents they scrutinized, Liu et al. were able to more specifically state that "from 601 to 900 AD the regional mean crop yield had a significant (P < 0.01) negative trend with the rate of -0.24% per decade," as the overall climate cooled. But superimposed upon this long-term linear decreasing crop yield trend, they found there were several periods of warming, which ultimately enabled them to confirm that "high crop yield occurred generally under the warming climate background." In fact, they were able to quantitatively conclude that "crop yield increased by 6.9% per 1°C warming," which they say "was slightly less than the estimation of 7.5% grades per 1°C warming from Su et al. (2014)."

It would appear, therefore, that global warming - if it is ever to begin again following its current 18-year hiatus - may very well prove providential in terms of boosting crop yields and enhancing food security, which is a much more optimistic assessment than that presented by the IPCC.

Braudel, F. 1992. Civilization and Capitalism, 15th-18th Century. Vol 2. University of California Press, Berkeley California, USA.

Dong, G. 1985. Full Tang Texts. Zhonghua Book Company, Beijing, China.

Ge, Q.S. 2010. Historical Climate Change During the Past Chinese Dynasties. Science Press, Beijing, China.

Ge, Q., Fang, X. and Zheng, J. 2003. Quasi-periodicity of temperature change on the millennial scale. Progress in Natural Science 13: 601-606.

Holopainen, J. and Helama, S. 2009. Little ice age farming in Finland: Preindustrial agriculture on the edge of the Grim reaper's scythe. Human Ecology 37: 213-225.

Li, Y.S. 1974. History of the Northern Dynasties. Zhonghua Book Company, Beijing, China.

Liu, X. 1975. Old Book of Tang. Zhonghua Book Company, Beijing, China.

Ouyang, X., Song, Q., Fan, Z. et al. 1975. Zi Zhi Tong Jian. Zhonghua Book Company, Beijing, China.

Parker, G. and Smith, M. 1997. The General Crisis of the Seventeenth Century. Routledge and Kegan Paul, London, United Kingdom.

Porter, J.R., Xie, L.Y., Challinor et al. 2014. Food Security and Food Production Systems. In: Climate Change 2014: Impacts, Adaptation, and Vulnerability. Working Group II. Contribution to the IPCC 5th Assessment Report - Changes to the Underlying Scientific/Technical Assessment.

Sima, G. 1975. Zi Zhi Tong Jian. Zhonghua Book Company, Beijing, China.

Song, M.Q. 2008. Commands Collection of Tang. Zhonghua Book Company, Beijing, China.

Su, Y., Fang, X.Q. and Yin, J. 2014. Impact of climate change on fluctuations of grain harvests in China from the Western Han Dynasty to the Five Dynasties (206 BC-960 /AD). Science China: Earth Sciences 44: 146-155.

Wang, P. 1955. Institutional History of Tang. Zhonghua Book Company, Beijing, China.

Wang, Q.R. 1985. Prime Tortoise of the Record Bureau. Zhonghua Book Company, Beijing, China.

Wei, Z., Yan, S., Kong, Y. and Xu, J. 1973. Book of Sui. Zhonghua Book Company, Beijing, China.

Zhang, D.D., Lee, H.F., Wang, C., Li, B., Pei, Q., Zhang, J. and An, Y. 2011. The causality analysis of climate change and large-scale human crisis. Proceedings of the National Academy of Sciences USA 108: 17,296-17,301.

Zhang, P. (Ed.). 1996. Historical Climate Change in China. Shandong Science and Technology Press, Jinan, China.

Posted 29 December 2014