Climate change affects St. Louis weather and plants — for better or worse?

It’s mid-February (2024), and from west-facing windows, the St. Louis area’s first real snowfall could be seen on the ground and trees in Forest Park, as well as the main drag. The weather event raised questions and concerns about climate change.

The St. Louis area has had unusually mild weather from November 2023 through the present. When past years have seen recordable snow levels and even disastrous ice storms in similar time frames, this year saw record high temperatures — 70s and 80s in the week of February 26, and drastic changes, from 84 degrees on February 27 to 27 degrees on February 28. There have been a few days of extreme cold this winter, but not even a week’s worth at a time. It hardly seemed worth using the word winter.

While these conditions might make life more comfortable and easier to navigate, it’s hard to relax because the instinct is to assume that a real winter is still to come. The potential impact on plant health or growth, and water levels, is also worrisome without much snow to melt and add to the aquifers. Flowering plants must be confused about blooming — buds had already appeared on trees around the city in February. Last year, the weather was so challenging that forsythias failed to bloom entirely, and other flowering trees and plants died off, while formerly solid-looking hedges thinned out and became straggly.

The visual aspect only adds to weather confusion these days — it can be 10 degrees out, but the sun is shining, the sky is blue, and the world looks bright and welcoming.

The U.S. Department of Agriculture (USDA) appears to agree that the St. Louis climate has changed: Its new plant cold hardiness map moved St. Louis City and County from Zone 6 to Zone 7, because winters in the region have become warmer. The USDA used improved data from more weather stations compared to the past for its current cold hardiness map.

It might take a decade to determine both whether the area really is warmer and what that means for gardeners and the public in general, according to Daria McKelvey, supervisor of home gardening information at the Kemper Center of the Missouri Botanical Garden in St. Louis. “We still recommend Zone 6,” McKelvey said.

Zone changes may suggest effects of global warming, but according to the USDA, “changes in zones are not reliable evidence of whether there has been global warming,” regardless of personal observations.

Efforts are in place to address climate change and its impact. The Smart Surfaces Coalition, for instance, aims to “help cities make ‘smart’ surface decisions by demonstrating the value of surfaces that manage the sun and rain … cities around the world can reduce extreme summer heat, minimize flooding, improve public health, create jobs and advance equity — all while saving money.”

The coalition recommends using trees, cool and green roofs, solar PVs, reflective and porous pavements, bioretention, low- and zero-carbon concrete, and combined surfaces to manage changing conditions, especially in dense urban areas.

The issue goes beyond St. Louis, of course. According to a recent study published in Nature, melting polar ice caps are changing the rotation of the Earth, which could have a “slight impact” on how long humanity might last. Study author Duncan Agnew, a geophysicist at the University of California at San Diego, told the Washington Post, “Global warming is managing to actually measurably affect the rotation of the entire Earth. Things are happening that have not happened before.”