While the Olympic Games weren't disrupted by the weather, the UK has still just had the wettest summer for 100 years. In contrast the US has experienced scorching temperatures and the worst drought in over 50 years, withering crops and prompting headlines of a new global food crisis. The US Department of Agriculture has slashed its estimate of the size of the domestic corn harvest by more than a quarter since its first estimates in May and corn and soybean prices have reacted by rising sharply. But are the consequences of the poor harvest in the US as significant as the raft of other, more subtle and long-term trends affecting the global food chain?

The Victorians had a helpful metaphor for describing slow moving trends: the 'boiling frog'. If a frog is placed in hot water, the theory goes, it will immediately jump out. But if it is placed in cold water and then slowly heated, it will not recognise the danger and will ultimately be boiled. We haven't attempted this experiment but the idea does capture rather well the way in which people often struggle to recognise or react to very gradual changes in their environment.

For the global food chain, the first gradual change - the first frog if you will - is the steady increase in the World population. In 2011, the number of people on the planet passed the 7 billion mark for the first time, doubling the figure for 1970. And the number of mouths to feed continues to grow, by about 70 million each year, and is forecast to reach 9.3 billion by 2050. Most of this growth comes from large developing countries such as India and Nigeria (interestingly, China's population - though very big at over 1.3 billion - is not growing due to the 'one child' policy).

David Fuller's view We have long known from Arctic and Antarctic ice core samples, and also geological discoveries, that Planet Earth's climatic history has been subject to extreme variations in temperature over many millions of years. We also know that the last 10,000 years or so have been remarkably stable, punctuated by two mini ice ages.

The next mini ice age, which you may recall a number or climatologists were predicting only 15 to 20 years ago, will have a devastating affect on our food supplies. However, the more immediate risk according to the same climatologists and most of their brethren is climate change in the form of global warming. If they are correct this time, and they are not without some worrying evidence as you know, then our food supplies are at risk of longer-term disruption.

The extent of this threat is impossible to know and weather turbulence is certainly not unprecedented in our era. However, the trend of diminishing ice caps and glacial melt elsewhere has not been seen to such an extent by anyone alive today. Consequently, we should be concerned although a gradually warming climate, should the trend of recent years continue, would produce both agricultural winners and losers. Heat and drought would be considerable problems for any of our main agricultural regions, but warmer climates and more moisture elsewhere would create new opportunities for farming.

Meanwhile, agricultural funds are a fashionable theme, although I am far from certain that they offer any additional protection for investors in the event of continuing climate change. With no disrespect to Sarasin or any other investment management firm offering agricultural funds, if foods are the theme I would rather hold some of the Dividend Aristocrats in this sector. Nestle has long been a Fullermoney favourite and Eoin frequently reviews companies in the food industry.