The USDA recently released new plant hardiness zones – updating maps from 1990. While some areas look different just because finer details were possible, there are clearly significant differences between the maps that are due to longer growing seasons and warmer nights at the bookends of the growing season. Those shifts in plant hardiness are an obvious manifestation of shifts that have already occurred in the climate. More shifts will continue to become apparent in the years ahead.
Where did most of the changes occur? As the comparison map below shows, at higher latitudes and higher altitudes – in the same locations that have warmed the most to date.
Look at the northern tier and the Rocky Mountains. Shifts from Zone 3 to 4 up north and from Zone 4 to 5 and Zone 5 to 6 throughout the Rocky Mountains are most apparent. Other changes can also be seen in smaller regions across the country.
The plants are simply responding to the changes in the climate. No cosmic rays or long solar minimum precipitated these changes. Readers should keep a simple fact in mind: these shifts are in response to the climate forcing leading up to the 1980s. These shifts do not yet represent the forcing of the past 30 years. How different will the maps of 2100 look?