More Warm Spring Days

While most of the country is comfortably into spring, signs of hotter weather are looming. Phoenix had its first 100 degree day in late April, more than two weeks earlier than the historical average of May 12. And the National Hurricane Center has already looked at systems for potential tropical development. As human-caused climate change continues, springs are heating up across the country.

Climate Central assessed the last half-century’s warm-up by plotting the annual number of spring days with above-normal temperatures. Of the 242 cities analyzed, 97% recorded an increase in warm spring days since 1970. There was an average increase of 10 warm spring days in that span — that’s a week and a half. Seven cities now experience more than a month of additional warm days, led by Tucson, Phoenix, and Las Vegas. All seven of those cities are in the Southwest, where spring is the fastest-warming season. The extra heat accelerates the evaporation that can lead to drought and stressed water supplies, affecting agriculture and energy systems as well as cities and towns.

Nationwide impacts of warm springs include longer pollen and pest seasons. As the spring and fall have brought more warm days, the growing season (and therefore allergy season) has lengthened by two weeks on average. Longer pollen seasons are affecting more and more Americans, as the rates of hay fever and asthma have nearly tripled in the last few decades. While a longer growing season may help some farmers, the ranges of familiar crops are shifting north. Warmer springs are also increasing the demand for air conditioning, driving up energy costs in some areas. And disease-carrying pests like mosquitoes and ticks are coming out earlier as well. Unless we quickly curb our climate-warming emissions, these warm spring days will increasingly blur into less tolerable summers.Methodology: The graph indicates the number of spring days above the 1981-2010 NOAA/NCEI climate normal. For each month, we counted the number of days when the daily average temperature departure from normal is greater than zero. The months of March, April, and May (meteorological spring) were analyzed.