When the Arctic Melts
October 09, 2024 at 05:47PMIn a piece that’s equal parts history and science, Elizabeth Kolbert visits Greenland to meet and learn from people studying climate change. While it’s undeniable that human-fuelled global warming is altering our weather patterns in surprising ways, our influence on the planet is but one part of its long and complex story.
Most scientists believe that ice ages—there have been at least ten of them over the past two and half million years—are initiated and terminated by periodic shifts in the Earth’s orbit, caused by, among other factors, the tug of Jupiter and Saturn. But orbital shifts produce only slight changes in the amount of sunlight that reaches different parts of the globe at different times of the year. Such slight variations are insufficient to explain the growth and subsequent retreat of massive ice sheets. Rather, it seems, the orbital shifts act like a trigger, setting off other processes—feedbacks—that greatly amplify their effect. One relatively straightforward feedback features albedo, from the Latin word for “whiteness.” Ice and especially snow have a high albedo. They reflect lots of sunlight back to space. Thus, as an ice sheet grows, the planet absorbs less energy. This has a cooling effect, which encourages the buildup of more snow and ice, which results in more reflectivity, and so on. Start to melt an ice sheet and the same cycle spins in reverse.
Today, feedbacks are, to put it mildly, a growing concern. A report published last year by more than two hundred researchers from around the world noted that many of the systems that determine the climate exhibit nonlinear behavior. Such systems may “shift to a very different state, often abruptly or irreversibly, as a result of self-sustaining feedbacks.” The researchers identified two dozen potential “tipping systems,” among them the Greenland ice sheet.
At a certain point, the report warned, feedbacks could become so powerful that, even if CO2 emissions were cut dramatically and temperatures stabilized, the ice sheet would continue to shrink, possibly until it collapsed. The “best estimate” of when this critical threshold will be reached is when average global temperatures rise 1.5 degrees Celsius—roughly three degrees Fahrenheit—above preindustrial levels. Even after that line is crossed, it will take many centuries for the changes set in motion to play out. Still, as a practical matter, there will be no going back. When it comes to tipping systems, the future is in our hands until it isn’t.
from Longreads https://longreads.com/2024/10/09/when-the-arctic-melts/
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