Climate change and the rising global population are putting pressure on farmers to improve productivity. This in turn plays into the hands of companies such as Syngenta, which supplies insecticides, fungicides and genetically modified seeds. A surge in prices for agricultural commodities (the S&P GSCI agriculture index is up 16 per cent this year) adds to the bull case. Investors, starved of growth stories elsewhere recently, have been piling in, with Syngenta shares up 22 per cent since January. They now trade on 16 times forecast earnings.