Warming Nights

By Susan Littlefield

We hear a lot about climate change and global warming these days, and as gardeners, we wonder not only how these trends will affect the world as a whole, but what it will mean for the plants growing in our own backyards. Some of what we can expect will be clearer when NOAA's National Climatic Data Center releases its latest version of the U.S. Climate Normals this month. In a recent article in NOAA's Climate Watch Magazine, Jennifer Freeman, a science writer with the American Meteorological Society, takes a look at how the figures have changed and what this may mean for plants in our gardens and in the wild.

Updated every decade, the climate normals are 30 year averages of weather information. As each new decade's figures are added in, those of the trailing decade are dropped. Starting this month, "normal" weather will be a little different than what was considered normal over the past decade.

The new 30 year climate normals period now runs from 1981 to 2010. Since the decade of the seventies was unusually cool and the past decade was the warmest ever recorded, it's not surprising that the average temperature for most locations rose. But what is surprising is that many parts of the country actually had cooler average maximum temperatures in July in the 2001-2010 period than they did 30 years earlier. It was the average overnight low temperatures, not the daytime highs, that changed most compared to the 1970's, resulting in an overall average temperature increase for all states.

How will these warmer nights affect plants? Some pest problems may increase. For example, the woolly adelgid that threatens hemlocks in the East and the pine bark beetle that is attacking forests in the West may both benefit from warmer winter nights. The growing range of some plants may change, with some species surviving farther north than before, while others may see the southern limits of their range shrink northward. Pollination patterns may change as plants bloom earlier in the spring.

To read more about the new climate normals and plants' response to warmer nights, go: The New Climate Normals.

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