Climate change is speeding up the return of leaves and flowers, but by just how much?
If you’ve read Jennifer Egan’s Pulitzer Prize-winning novel, A Visit from the Goon Squad, you’ll know that the end of the book is set sometime in the 2020s, in a futuristic New York City with 89 degree days in February and trees that bloom in January.
Scientists have been saying for years that climate change will cause briefer and more delayed snowfall seasons, together with longer and earlier growing periods for plants. And I’ve been wondering since I read Egan’s novel: Climate change may be scrambling the seasons, but trees leafing in January a mere dozen years from now? How close to reality might her vision be? How much earlier will the leaves arrive in coming years?
The U.S. Environmental Protection Agency predicts that average global temperatures will increase by 2 to 11.5 degrees Fahrenheit by 2100. But a paper that appeared in Nature this spring suggests we have been lowballing our estimates in how this might affect leafing plants.
Experiments that exposed plants to artificially warm conditions have, until now, formed our current assessment: that for each 1.8 degree Fahrenheit increase in temperature, flowering and leafing should occur between almost two and three-and-a-half days earlier. And many observations of wild plants have agreed with this, indicating that flowering and leafing shift two-and-a-half to five days earlier per 1.8-degree temperature increase.
But based on their observations of over 1,500 plant species in the wild and in experiments, the authors of the Nature study predict that in many parts of the world, leafing and flowering will actually occur a full 5 to 6 days earlier with each 1.8 degree increase in temperature.
In New York City, leafing currently occurs around early April. At this new rate, if the EPA is right and temperatures increase 2 to 11.5 degrees by 2100, leafing could occur anywhere from 6 to 38 days earlier — meaning in 2100 we’d be seeing leaves returning sometime between late February and late March.
The worst-case scenario, trees sprouting leaves in February, is pretty unnerving. But at least it won’t be as startling as the vision in Egan’s novel. A decade from now, barren trees and sweaters will still likely be the norm for February in New York City.