The arable land that moved uphill

Maps of where crops grow are usually treated as fixed features of a country. Over a human lifetime they move, and in several regions they are moving now.

The mechanism is simple. Each crop has a range of temperatures within which it yields well, and a range outside which it yields badly or not at all. As average temperatures rise, the band of land suitable for a given crop shifts towards the poles and, in hilly country, uphill. Coffee is the clearest case: the land where it grows best in several countries has moved several hundred metres higher in thirty years.

The difficulty is that land does not move with the band. Higher ground is often steeper, thinner in soil, already forested or already occupied. A farmer told that their crop will do better two hundred metres up is being told something true and unusable, because the two hundred metres belong to somebody else or to nobody and cannot be ploughed.

This is why adaptation is slower than the physical shift that drives it. Changing crop is possible but expensive and requires knowledge the household may not have. Moving is possible and means leaving. Staying and accepting lower yields is the most common choice, and it is rarely described as adaptation although it is what most people actually do.

Any honest account of the next thirty years has to include that third option, because it is the one the largest number of families will take.