January 2020 was the warmest on record (over 141 years) according to NOAA’s National Centers for Environmental Information. Karin Gleason, a NCEI climatologist, said earlier this month that global average temperatures in January were 2.05 degrees Fahrenheit above average. This is a little higher than the now second warmest January ever, which occurred in 2016.
Climate Central, an independent organization of leading scientists and journalists that research and report facts about the climate and its impact on the public, recently analyzed how temperatures during meteorological spring, March 1 – May 31, from 1970 through last year.
This analysis shows most of the United States having warmed during the 49 years. The top increases occurred in the Southwest—where spring is the fastest-warming season. Reno, Nev. topped the list with an increase of 7.2°F, followed by Las Vegas, Nev. (6.4°F), El Paso, Texas (5.8°F), and Tucson, Ariz. (5.8°F). In general, 81% (197) of the 242 cities analyzed warmed by at least 1°F over the past fifty years. The Southwest also saw the greatest jump in the number of spring days above normal, with 79% (191 of 242) of cities recording an increase of 5 or more days.
The data in Colorado Springs shows a similar story, rising 2.8 degrees Fahrenheit. This has also led to a larger number of days with above-average temperature during the transition from winter to summer. Looking at the yellow line in the graphic below, showing the data for individual years, you can clearly see that there are warmer years and colder years, but in the overall trend you likely notice the even the colder years are having more days above average.
Interestingly enough, the average date of last freeze has gotten later in Colorado Springs, even with an overall warming trend. 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.
I attribute the delay in latest freeze for Colorado Springs to the air overall being drier in the spring as the atmosphere has warmed. Dry air is more susceptible to changes at night and during the day as it cools off and warms up more efficiently than air with high moisture content.
The Climate Central analysis of 195 cities across the nation 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.
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. The prevalence of allergies has skyrocketed in recent decades. In 1970, about 10 percent of Americans suffered from hay fever, which is caused by airborne allergens like pollen and mold spores; by 2000, 30 percent did. The rate of asthma — which often occurs alongside pollen allergies — nearly tripled between 1980 and 2010. Symptoms range from uncomfortable to dangerous, with asthma killing about 3,500 Americans in 2016.
Not only are the symptoms miserable to deal with, but treating them costs the U.S. an eye-watering sum of money— more than $18 billion each year.
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.