We may have missed out on the last two winter storms, but frosty nights have been plentiful. While the growing season in Wisconsin hasn’t officially started, it’s likely to begin in the next couple of weeks.
The last freeze is an important marker of the beginning of the growing season—when plants emerge from their protective phase of winter dormancy in order to grow, develop flowers and reproduce. Our partners at Climate Central analyzed 195 cities and showed that 80% (156) are experiencing their average last freeze earlier in the season, with 54% (105) recording that shift by more than a week earlier than 50 years ago.
Since 1970, Madison has seen it’s own dramatic change of about two weeks. This has taken our average last freeze from around the middle of May to right around the start of May.
More days above freezing has led to a longer growing season, which in turn means a longer allergy season. Seasonal allergies are one of the most common chronic conditions in the U.S., with as many as 1 in 6 Americans affected by them. Not only are the symptoms miserable to deal with, but treating them costs the U.S. an eye-watering sum of money—between $2 and $5 billion annually.
Similarly, a longer growing season also means longer pest seasons. Warmer, more humid air makes for more favorable conditions for mosquitoes and even changes in behavior of ticks. Warming spring temperatures can also interfere with the timing (phenology) of important natural events such as hibernation, bird migration, and pollination.
In a changing climate, the cultural hallmarks of our favorite seasons are being altered. Working to address climate change by lowering greenhouse gas emissions is one important way that we can turn over a new leaf and protect our natural world in the coming decades.
METHODOLOGY: Analyses used 1970-2019 data from the Applied Climate Information System. Locations without a consistent freezing season (defined as fewer than 30 annual nights of sub-freezing temperatures) were excluded from the last-freeze analysis.
Displayed trend lines are based on a mathematical linear regression. Climate Central’s local analyses include 244 stations. However, for data summaries based on linear trends, only 242 stations are included due to large data gaps in St. Johnsbury, Vt. and Wheeling, W. Va.
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