This is what happened this year. This is what seems likely to happen in subsequent years. Here is why: A paper this year by the world’s leading climate scientist, James Hansen, shows that the frequency of extreme heat events (such as the droughts which hammered the US and Russia) has risen by a factor of about 50 by comparison with the decades before 1980. Forty years ago, extreme summer heat typically affected between 0.1 percent and 0.2 percent of the globe. Today it scorches about 10 percent.
“We can project with a high degree of confidence,” the paper says, “that the area covered by extremely hot anomalies will continue to increase during the next few decades and even greater extremes will occur.”
Yet these extremes do not feature in the standard models predicting changes in crop production.
If the mechanism proposed by another paper is correct, it is not just extremes of heat that are likely to rise. The jet stream is a current of air traveling westwards around the upper northern hemisphere. It separates the cold wet weather to the north from the warmer, drier weather to the south. Wobbling along this ribbon are huge meanders called Rossby waves. As the Arctic heats up, the meanders slow down and become steeper. The weather gets stuck.
Stuck weather is another way of saying extreme weather. If the jet stream is jammed to the north of where you are, the weather stays hot and dry, and the temperature builds up — and up. If it is lodged to the south of you, the rain keeps falling, the ground becomes saturated and the rivers burst their banks. This summer the UK and the US seem to have found themselves on opposite sides of stuck meanders and harvests in both countries were savaged by opposing extremes of weather.
This is where we stand with just 0.8?C of global warming and a 30 percent loss of summer sea ice. Picture a world with two, four or six degrees of warming and a pole without ice, and you get some idea of what could be coming.
Farmers in the rich nations can adapt to a change in average conditions. It is hard to see how they can adapt to extreme events, especially if those events are different every year. Last winter, for example, I spent days drought-proofing my apple trees, as the previous spring had been so dry that — a few weeks after pollination — most of the fruit shriveled up and died. This spring was so wet that the pollinators scarcely emerged at all: It was the unfertilized blossom that withered and died. I thanked my stars that I do not make my living this way.
Perhaps there is no normal any more. Perhaps the smooth average warming trends that the climate models predict — simultaneously terrifying and oddly reassuring — mask wild extremes for which no farmer can plan and to which no farmer can respond. Where does that leave a world which must either keep raising production or starve?