Michigan Fruit Trees and Global Warming

There are all kinds of evidence that we are in a period of global warming. Many of the examples don’t have so much to do with temperature as with heat. Glaciers, for instance, stay pretty much at the same temperature under the surface. But ice requires 80 calories of heat per gram to melt, without changing the temperature. You can see that when you put ice cubes in your tea. You can also see the effect of global warming on Michigan fruit trees.

We live in an area rich in fruit-growing with apples, peaches, pears, cherries, grapes, and blueberries being major cash crops. My friends who make their living with Michigan fruit trees are very upset with the current weather cycle because it has not been cold enough. Fruit trees require time and temperature to know when to blossom and when not to. They do this by a sophisticated design system. Most fruit trees need a minimum of 250 hours of temperatures between 35 and 50 degrees Fahrenheit (2 to 10 degrees Celsius), and some require up to 1000 hours. Temperatures below freezing don’t count.

The “chilling hours” are sensed by the buds on the trees, not the roots. The wisdom in this system is obvious. Michigan winters usually have many days when the temperature goes below 10 degrees C, but there are also those rare days when the temperature gets very warm. This past winter, we had fewer than normal hours in the required temperature range. The buds have not gotten enough chilling to tell them to open. If they didn’t have the built-in time requirement, you can understand what would happen. The first time the temperature dipped below 10 degrees followed by a warm day, the buds would open and blossom only to be killed by the next cold snap.

Trees that are native in southern latitudes don’t bear fruit well when they are moved north. God has suited plants to different climates as well as other environmental factors. Orchards are found near bodies of water for several reasons. One of them is the tempering effect the water has on the air temperature. The presence of Lake Michigan provides a heat sink for our Michigan fruit trees that is as important as the moisture itself. The Psalmist seems to have had some idea of this when he compares a righteous person to a tree: “Blessed is the man who does not walk in the counsel of the wicked … He is like a tree planted by streams of water, which yields its fruit in season” (Psalms 1:1-3).

My fruit-growing friends have learned to understand and work with God’s design for their trees, but sometimes weather anomalies can frustrate their best efforts.

— John N. Clayton © 2020