10 Jul

Map of the Week: Plant Hardiness Zones

By Nigel Jaffe

How cold a certain region gets in winter affects much more than just the heating bills: it’s actually one of the most important factors in agriculture across the globe. Seasonal highs and lows determine which plants can be grown where, setting standards by which growers determine how successful particular crops will be in a given season and location. “Hardiness” in plants refers to their ability to survive harsh growing conditions, such as temperature, water levels, and wind. By averaging the coldest temperature in each year across several decades, analysts can create and map 30-year “plant hardiness zones,” comparing shifting historical temperatures while using current data to make predictions for the future.

This GIF depicts the evolution of plant hardiness zones in the continental United States across two different time spans: one marked “2000,” representing the average lows between 1971 and 2000, and one marked “2010,” representing the average lows between 1981 and 2010. An additional map illustrates predictions for the period between 2011 and 2040, marked “2040.”

When taken together, these three maps clearly show that temperatures are on the rise across the nation. Zones in every state have steadily become warmer over time, appearing to creep northward as the maps approach the present day. Meanwhile, the predicted zone distribution for 2040 illustrates a striking increase in temperatures across the board. The darkest green section (Zone 3), which delineates some of the coldest areas, is projected to vanish almost entirely by 2040, with only a sliver in the upper midwest remaining. Meanwhile, warmer sections, such as Zone 9 and Zone 10 (darker reds), are expected to make significant advances throughout the south.

All of these figures, both historical and predicted, demonstrate the global scale and impact of climate change. These shifting zones are significant not only to the nation’s innumerable growers and farmers, who rely on stable weather to produce crops effectively, but to wildlife across the nation, many of which inhabit vulnerable, delicate ecosystems. Maps such as these, which appear at first glance to be useful only to niche audiences—in this case, farmers—actually shed light on a more nuanced issue. They provide a means through which to visualize an ongoing phenomenon while spreading awareness of implications of climate change that reach far beyond the realm of agriculture.