Papers published this week detail the effects on our forests, our food supply, and our health.
By Nathan Collins
A Douglas fir. (Photo: Diana Robinson/Flickr)
Rising sea levels represent probably the most visible effect of climate change, with global drought coming in at a close second. But as three papers published this week in Proceedings of the National Academy highlight, flooding coasts and bone-dry inlands are just two of the specters we face in the century to come: There are also serious threats to Douglas fir trees, one of the main sources of construction lumber in the United States; fisheries in Lake Tanganyika, a key source of food in the region; and our own health, through growing exposure to the bacteria that causes cholera.
Douglas firs are “one of the most ecologically and economically important coniferous species in the western United States,” write Christina Restaino, David Peterson, and Jeremy Littell. Despite that fact, past researchers have not taken a detailed look at how climate change might affect them. Restaino, Peterson, and Littell first took core samples from Douglas firs in 122 locations in 11 Western states, which gave them a detailed record of tree growth over the last century. They next compared those patterns to historical climate data to look at how specific, “plant-relevant” variables affected tree growth.
The results suggest Douglas firs are most sensitive to vapor pressure deficit, a measure similar to relative humidity that increases in response to rising temperatures. As temperatures go up over the coming century, the researchers explain, increasing vapor pressure deficit will curb Douglas fir growth, creating problems for carbon sequestration, biodiversity, and forest productivity.
Algae, which other lifeforms rely on for food, declined substantially in response to rising temperatures.
Meanwhile, global warming is bringing ever-higher temperatures to the waters of Lake Tanganyika, with corresponding problems for the plants and animals living in Africa’s deepest lake, writes a team led by Andrew Cohen. Cohen and his fellow researchers took sediment core samples from three areas of the lake bed, from which they extracted fossils and chemical markers of age and organic compounds that serve as proxies for temperature at the time they were deposited on the lake bed.
The results show warming trends dating back 150 years, with warming during the 20th century “unprecedented” in the past millennium-and-a-half, and a corresponding decline in the abundance of fish and other organisms. Of particular concern, algae, which other lifeforms rely on for food, declined substantially in response to rising temperatures, suggesting that the lake’s ecosystem could collapse as a consequence of global warming—and with that ecosystem, a major source of food for people living in the region.
Finally, there’s the threat of cholera, a disease we often associate with untreated water in developing countries, and one that kills as many as 142,000 people every year. It’s known that warming ocean temperatures are going to impact a whole slew of marine creatures, including the plankton to which the cholera-causing bacteria Vibrio cholerae (and other members of the vibrio genus) often attach—although exactly how is less clear. To remedy that problem, a team of researchers led by Luigi Vezzulli and Rita Colwell turned to the Continuous Plankton Recorder, which comprises plankton samples dating back as many as 50 years.
The researchers searched those samples for signs of vibrio species, from which they constructed a “vibrio-relative abundance index.” The index is strongly correlated with sea surface temperatures, the researchers find, meaning that, as ocean temperatures increase, so too will the prevalence of vibrio species. What’s more, those trends appear to be correlated with a global increase in cholera cases, the researchers note—suggesting that a rise in temperature will bring with it an uptick in incidence of the potentially deadly disease.