Happy meteorological spring!
Despite record cold in parts of the country, record highs in March are outpacing record lows by a 3 to 1 ratio (according to Guy Walton’s NCEI-based records database) for this decade. And as the climate warms, so are spring temperatures for most cities across the U.S.
In the past half-century, spring temperatures have trended upward at least 1°F in 84 percent of the 244 cities we analyzed. Only 1 percent have experienced a 1°F cooling trend during that same period. This equates to an average spring warming of more than 2°F for the contiguous U.S. And while winter may be the fastest warming season for much of the country, spring is the fastest warming season in the Southwest. Las Vegas and Tucson have warmed more than 6°F since 1970, while temperatures in El Paso and Phoenix have risen more than 5°F.
Higher temperatures mean more frost-free days, which can open the floodgates for pollen and pests. With the last freeze coming sooner (and the first freeze happening later), the growing season has lengthened by 10 days in the Northeast and 17 days in the West. While this may allow more time for crops, it also means a longer allergy season, from tree pollens in the spring to ragweed in the fall. According to a PNAS study that sampled 10 locations from Texas to Canada, pollen seasons got two to four weeks longer from 1995 to 2009 — with the highest increases in northern areas. Earlier springs can also hasten the arrival of mosquitoes, ticks, and agricultural pests — potentially reducing crop yields.
If greenhouse gas emissions continue to rise, the arrival of spring in 2050 could be two weeks earlier than in recent years. Those future Marches may be milder, but their fearsome pollen totals may come “in like a lion” nonetheless.