Since the 1850s, when Henry David Thoreau was living at Walden Pond, the mean annual temperature in the Concord area has risen by 4.3 degrees. And that warming has had an effect.
According to a study by scientists from Harvard University and other research institutions, 27 percent of the native plant species that Thoreau documented have gone missing, and another 36 percent are under threat, Carolyn Johnson reports in the Boston Globe.
Explains researcher Charles Davis, quoted by Harvard Magazine: “Climate change will lead to an as-yet unknown shuffling of species, and it appears that invasive species will become more dominant.”
What makes the situation at Walden unusual is that Thoreau kept meticulous records, making it possible for scientists to document changes in ways that just can’t be done in most parts of the country. As University of Wisconsin researcher Mark Schwartz told Wired.com back in 2008, when the study was being conducted:
Whenever you have an opportunity to get a dataset where someone who has made very careful efforts to observe things in a systematic way, it gives you a snapshot of a particular time period and lets you make comparisons.
And before you say “global warming is good for you,” take a look at this assessment from Harvard scientist Davis:
Invasive species can be intensely destructive to biodiversity, ecosystem function, agriculture, and human health. In the United States alone the estimated annual cost of invasive species exceeds $120 billion. Our results could help in developing predictive models to assess the threat of future invasive species, which may become greatly exacerbated in the face of continued climate change.