How about them apples?
Why we need accurate predictions of climate change
If you are a regular reader, you’ll know that I have been suggesting we need a greater focus on adapting to climate change because I don’t think we’ll slow it down much, let alone stop it. If you think I’m wrong, then first take a look at my post, World Energy Consumption. (3/5/2024) What you will see is that while solar and wind energy production has increased, so has fossil fuel consumption. In fact, the trends in fossil fuel consumption really have changed. Given this, I thought I should provide an example of why honest future temperature predictions are important. Let’s talk about apples (and pears) and why they are a northern crop.
Here is the key quote from the article What Are ‘Chill Hours’ And Why Do They Matter?
The typical apple or pear tree’s total ‘chill requirement’ has been estimated to be 1,200 to 1,500 hours (at 5°C – 7°C) by Ryugo1 in 1988 and circa 1,000 hours (at 6°C – 9°C) by Heide & Prestrud2 in 2005.
In short, the chill requirement is the number of “cold” winter hours for the tree to flower and hence fruit after the winter. This is largely an all-or-nothing game. If the winter is too warm, you simply won’t get any apples. There are some locations in the U.S. that grow apples now that may not be able to grow them at some point in the future, depending on how much warming we get. The question then becomes: where and when should orchards be relocated? This would depend on your climate change predictions. If you believe we will get to net zero, you might also believe that we don’t have to worry about this. On the other hand, I would disagree.
My goal was to calculate the chill hours for Ithaca, NY, to see how that has changed. Unfortunately, I haven’t found hourly temperature data, but I do have the daily minimum temperature. Let’s go to the data, which turns out not to provide the results I expected, which is why we go with data and not beliefs, but it is still instructive.
Figure 1 is the number of winter days where the minimum temperature has dropped below 45°F (about 7°C).
The first thing you might notice about Figure 1 are the years 1977, 1992, 1997, and 2007, partly because I labelled them. Were those crazy warm winters? Maybe, but that isn’t it. Outliers like this need an explanation. In this case, each of those years is missing a full month of data: Dec, Nov, Dec, and Feb, respectively. If those years are kept, we get a downward trend in the regression line. But now look at Figure 2.
It turns out that we have a slight increase in the trend for the number of days below 45°F, but the line isn’t significant (p = 0.2733) and the R-square is almost 0 (0.01). In other words, there is no trend. This doesn’t calculate chill time exactly, but it is a good sign for Ithaca that the temperature is still going below 45°F, giving us a chance at some chill hours.
It turns out that when I checked the number of days below 40°F, 35°F, and 32°F, the results were the same. Figures 3, 4, and 5 show these results.
In all cases, the regression line isn’t significant, and the R-square value is close to 0. In other words, there is no trend, although there is lots of variation. I was bit surprised by this so I thought I’d look at a shorter time period. For example, Figure 6 shows the number of days below 32°F starting in 1970, and while the regression line has a slight downward trend, it isn’t significant. I’m still a bit surprised.
What I think is happening is that these cutoffs are too high. Most days in the winter, we get below freezing with plenty of room to spare. What I should see is some change at lower temperatures. For example, Figure 7 shows the days below 20°F.
In Figure 7, the regression line is significant (p = 0.0117), although the R-square value is still small (0.125). This also gives us a sense of why we aren’t seeing downward trends (yet) in the other graphs. If we have 40–50 days below 20°F, then it isn’t surprising that we see 100 days below 32°F.
Conclusions
Although I was surprised at first, it does seem like we get plenty cold enough that apples are fine for the foreseeable future in terms of chill hours. But for how long? As this app here suggests, the Ithaca climate will be similar to Cherry Hill, Virginia, by 2080. Certainly, that would mean warmer minimum temperatures, but maybe still cold enough for the apples we currently grow.
The second point here is that it may not be that we can or can’t grow apples, but of what variety? Which then leads to the question of when one should start growing different varieties. You don’t plan an apple tree one year and get bushels of apples the next. The main point of today's post is that climate change has an impact on agriculture, particularly where and when we grow, and that accurate predictions are crucial in planning future agricultural production. As for other examples, maple syrup and dairy are northern products, while oranges are a southern product. How will global warming affect these industries? Assume net zero, then maybe little will change, but again, I’m not betting on that, so what’s the plan?
My last point is that chill hours is only one problem or example. One other issue that we have had in recent years is a warmer spring that has fruit trees bud out and flower, but then a more typical frost occurs, which kills all the flowers. Last year, a good half or more of our local apples were lost because of this. A few years ago, entire cherry crops were lost. We often talk about warming when increased temperature variation is just as much of an issue. What should we expect in the future from this type of temperature variation?
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