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So What's Wrong with a Little Global Warming

Be afraid (but don't panic). On the first day of spring, the only thing I was afraid of (maybe even a little panicked) was that I didn't have enough warm clothes.  I was in Boston, mid-afternoon, and the thermometer on my dashboard registered in the low 30's—that would be Fahrenheit.   Spring?  I don't think so.  I could see my breath, even though the sun was shining.  A couple of days later, as my wife and I were walking across a college campus in Maine that our California-bred daughter was checking out before applying, it was even colder, right around 18°F with a biting wind, in what should have been the heat of the day.  Although I didn’t actually ask, I didn't get the sense anyone was thinking too much about global warming, except maybe to say, “Bring it on.” It was right around then that the penny really dropped for me—if you live in a climate like this, a little global warming doesn't sound like such a bad thing.  Especially when they're telling you a major impact will be flowers blooming a week or so earlier.   Who in their right mind wouldn't want that to happen? Well, it depends what you’re willing to sacrifice—nothing comes without a cost, after all.   In this case, the sacrifice seems to be loss of many of the flowers we like, and increasing numbers of the kinds of plants we don’t particularly care for.  At least that’s what seems to be going on at one of nature’s icons just a short distance outside of Boston—the woods around Walden Pond.  These are the same woods where Henry David Thoreau found his muse, and where he passed the time by carefully recording what plants first bloomed on which days.  Some 150 years later— that is to say, from 2003 to 2007— Harvard and Boston University biologists systematically strolled those same woods and replicated Thoreau’s surveys. What they found, as they reported in the Proceedings of the National Academy of Sciences (PNAS, November 4, 2008, vol. 105, pgs., 17029–17033), was that, on average, around Walden Pond plants are indeed flowering about a week earlier than they were during Thoreau’s time, coincident with local warming of about 4.3°F over the past 100 years.  But hidden in that “average” are exactly which plants are doing well and which ones are not.  A disproportionately large number of weedy, non-native species are the ones blooming earlier; these plants seem to have the genetic and behavioral flexibility to take advantage of those earlier warmer temperatures and blast out their flowers, getting an early start on reproduction.  But the charismatic wildflowers—things like buttercups, anemones and asters, dogwoods, lilies, orchids, St. John’s worts, violets, and others are losing out.  For whatever reason, they seem not to have the ability to move their flowering clock forward to get a jump on spring.  As a result, they are declining in abundance, to the point where they seem on the road out of the area. Now the “be afraid” part. It turns out those wildflower species that are losing out belong to several different “families” on the evolutionary Tree of Life.  It’s not just one or two families—it’s more like 16.  And it’s not just one or two species in each family—it’s more like a quarter to a half of the species in each. What seems to be happening is a wholesale pruning of many branches of the Tree of Life around Walden Pond, with global warming being the chainsaw. Loss of aesthetics is one thing, loss of livelihood another.  That too seems on the horizon from global warming in the Northeast.  As we drive through Vermont, it’s hard not to notice the roadside signs to drop in and enjoy fresh maple syrup, a crop that pumps more than $13 million per year into the state’s economy.  Another recent study reported in PNAS (2008, vol. 105, pgs. 4197-4202) documents that in the past 40 years maples and other hardwoods in Vermont have been declining in their traditional growing areas, and marching to higher elevations in response to local warming of about 2°F.  Marching upslope is fine as long as you don’t run out of mountaintop, which is destined to happen.  In fact, models that link maples to their required climate indicate that the new center of the maple syrup industry is on the move not just upslope, but north, to Canada. As for me, I’m putting on my jacket (and my sweater and my vest) and heading south.  We’re continuing our drive down into New York, then we’ll circle back to Boston.  I think on the way I may stop at Walden Pond and see what’s blooming. ——— Since 1990, Anthony D. Barnosky has been on the faculty at the University of California–Berkeley, where he currently holds the posts of professor of Integrative Biology, curator of Fossil Mammals in the Museum of Paleontology, and research paleoecologist in the Museum of Vertebrate Zoology. Dr. Barnosky is author of the book Heatstroke: Nature in an Age of Global Warming. Click here to visit his website.