A Return to Cooler Growing Seasons?

David Archibald has an interest Mid-west growing season analysis on a guest post at WUWT.

Now that the Modern Warm Period is over and we are going back to levels of solar activity typical of the 19th century, it is apposite to look at what the climate was like then and how a return to 19th century-type climate will impact on agriculture.


Figure 4


What Figure 4 shows is that a century ago daily temperature minima during the planting season were three weeks behind what farmers experienced last decade. What is also interesting is that in the 1900 to 1910 decade there was a pronounced dip in temperatures in February. Last decade the dip was reduced and came forward by a fortnight.


Figure 5


Corn growth responds to heat. The concept of Growing Degree Days (GDD) captures that by taking 50°F from the average daily temperature. For example a daily maximum of 76°F with a minimum of 54°F produces an average of 65°F. Take 50°F from 65°F gives a result of 15 GDD for that day. Corn varieties have been bred to maximise productivity from recent climatic conditions and require 2,500 GDD to reach maturity.

Figure 5 shows that last decade corn crops could get to 2,500 GDD by mid to late August. A century ago maturity mightn’t be reached until the end of September. Normal first frost date for Whitestown is 10th October but 110 years ago the first frost was on 3rd September, ending growth for the season. Last decade averaged 177 days between the last spring frost and the first fall frost. In the first decade of the 20th century, the average number of days between these frost events was 147.

This is going to be an interesting location to watch for early and late frost events. I am going set a Google Alert for frost events at Whitestown.  Stay Tuned

Grapes in California’s Napa Valley respond to GDD and I will take a look to see if similar data is available at a location in the Napa Valley.

The changing length of the growing season in an indicator the lack of sunspots could have an impact on the climate.  It is also a warning sign for growers and agricultural agencies, who right now are focused on warming.



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