The shape of things to come

Gardeners in this area typically think of Memorial Day weekend as the date of the last hard freeze: time to relax, put your seeds in and enjoy the warmth. And certainly, this year it looks as though we have finally put the rigors of winter behind us, with Mother’s Day having marked the last of the killing frosts. But though that was the last freeze, it has left its mark with us: some buds and leaves, lured out exceptionally early by an unseasonable burst of warmth in early April, still linger curled and brown on the branches of certain plants. They are a reminder that, with the climate changing, the seasons will not always be what we have expected them to be.

Though the frost damage in the Upper Delaware did not appear to be widespread, it was notable to the extent that it did not confine itself to commercial crops—which one expects to be vulnerable because many of them did not evolve to survive without help in the climates in which they are grown—but to some natives as well. The photographs on this page show two such plants located in the Town of Fremont, NY: wild grape vines and a red mulberry tree. They will no doubt refoliate, but the mulberry will produce close to nothing this year and it looks like about half the bud clusters on the grape were destroyed.

Wild grapes and mulberries may not have commercial value, but they are part of our native food chain, and their dropping out of that chain has consequences for the habitat as a whole. If this were a once-in-a-while event, that still might not be such a big deal. But 114 years worth of weather readings, taken not far from here at the Mohonk Preserve in the Shawangunks and reported recently in the Journal of Applied Meteorology and Climatology, suggests that the warm-and-freeze sequence may be becoming increasingly common.

Consistent with climate change theories, the Mohonk measurements show a gain in average temperatures over the period of 2.63 degrees. Also consistent with global warming, the total number of yearly above-freezing days is increasing. But the growing season has not lengthened during the observation period. The reason is that all those above-freezing days are not grouped together neatly between the last and first hard-frost dates. Instead, there are more unusually warm days in between the first and last hard frosts—just as occurred this April.

To be sure, there are locations in the Northeast at which the growing season has lengthened somewhat during the period in question. But Mohonk is close enough to us for observations taken there to give us pause. Combined with the Mother’s Day freeze, they suggest some troubling possibilities. If nothing else, they help to remind us that climate change, even though it is related to increasing average temperatures around the globe, does not manifest itself in our backyard as evenly warmer temperatures year round. On the contrary, global warming leads to volatility, extremes and the disruption of patterns. This is why claims that the unusually snowy winter we just saw in Washington, DC proves that climate change is not occurring are completely off base. In fact, more frequent and severe storms are precisely what global warming theory predicts, and temperatures can be unusually cold on certain days or over short periods and still average out warmer over the year as a whole.

In addition, the type of destruction that this year’s warm-and-freeze pattern has wrought on native plants in the Upper Delaware region—plants that have evolved to succeed here over millennia—brings home in a very immediate way what climate change could cost us here. Should the combination of hotter temperatures in summer, deceptive hot spells in winter and vicious late frosts continue, it won’t just be that we will exchange our current flora and fauna for that, say, in the Carolinas. It would mean that the only plants and animals that could survive here are those that can both stand hotter summers—and the insects, fungi and so on that they bring with them—and bitter late freezes. That’s kind of a tall order, and most likely would mean a massive loss of diversity, an impoverishment of our environment and a loss to the planet.

This year’s losses of wild crops do not appear to have been extensive, but if the trend in the Mohonk data continues, the shriveled mulberries and grapes may be serving as canaries in the coal mine when it comes to the impact of global warming. They are a reminder that climate change isn’t something happening at some vague point in the future; it’s happening now.

Dr. Punnybone

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